tag:talks.cs.umd.edu,2005:/lists/22/feedQuICS Seminar2017-09-24T06:10:51-04:00tag:talks.cs.umd.edu,2005:Talk/8622014-12-17T11:48:38-05:002014-12-17T12:00:42-05:00https://talks.cs.umd.edu/talks/862Ground State Connectivity of Local Hamiltonians<a href="http://www.people.vcu.edu/~sgharibian/">Sevag Gharibian - Virginia Commonwealth University</a><br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">2115 Computer and Space Sciences Building (CSS)</a><br>Thursday, December 18, 2014, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 14px; line-height: 22px;">The study of ground state energies of local Hamiltonians is a natural generalization of the study of classical constraint satisfaction problems, and has thus played a fundamental role in quantum complexity theory. In this talk, we take a new direction by introducing the physically well-motivated notion of "ground state connectivity" of local Hamiltonians, which can be thought of as a quantum generalization of classical reconfiguration problems. In particular, ground state connectivity captures problems in areas ranging from quantum stabilizer codes to quantum memories. We show that determining how "connected" the ground space of a local Hamiltonian is can range from QCMA-complete to NEXP-complete (where QCMA stands for Quantum-Classical Merlin Arthur, a quantum generalization of NP). As a result, we obtain a natural QCMA-complete problem, a goal which has generally proven difficult since the conception of QCMA over a decade ago. Our proofs rely on a new technical tool, the Traversal Lemma, which analyzes the Hilbert space a local unitary evolution must traverse under certain conditions, and which may be of independent interest.</span></p>
<p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 14px; line-height: 22px;">Joint work with Jamie Sikora. No background in quantum computing is assumed.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9012015-02-06T15:35:41-05:002015-02-09T14:45:51-05:00https://talks.cs.umd.edu/talks/901The CHSH inequality: Quantum probabilities as classical conditional probabilitiesAndrei Khrennikov - Linnaeus University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Tuesday, March 17, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p>The celebrated theorem of A. Fine implies that the CHSH inequality is violated if and only if the joint probability distribution for the quadruples of observables involved in the EPR-Bohm-Bell experiment does not exist, i.e., it is impossible to use the classical probabilistic model (Kolmogorov, 1933). In this talk we demonstrate that, in spite of Fine's theorem, the results of observations in the EPR-Bohm-Bell experiment can be described in the classical probabilistic framework. However, the "quantum probabilities" have to be interpreted as conditional probabilities, where conditioning is with respect to fixed experimental settings. Our approach is based on the complete account of randomness involved in the experiment. The crucial point is that randomness of selections of experimental settings has to be taken into account. This approach can be applied to any complex experiment in which statistical data are collected for various (in general incompatible) experimental settings.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9022015-02-06T15:36:38-05:002015-02-06T15:36:54-05:00https://talks.cs.umd.edu/talks/902Quantum voting and violation of Arrow’s Impossibility TheoremNicole Yunger Halpern - Caltech<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Friday, March 20, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 14px; line-height: 22px;">We propose a quantum voting system in the spirit of quantum games such as the quantum Prisoner’s Dilemma. Our scheme violates a quantum analogue of Arrow’s Impossibility Theorem, which states that every (classical) constitution endowed with three innocuous-seeming properties is a dictatorship. Superpositions, interference, and entanglement of votes feature in voting tactics available to quantum voters but not to classical.</span></p>
<p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 14px; line-height: 22px;">This work was conducted with Ning Bao. Reference: arXiv:1501.00458v1.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9032015-02-06T15:37:46-05:002015-03-19T17:01:45-04:00https://talks.cs.umd.edu/talks/903Quantum simulations of one-dimensional quantum systemsRolando Somma - Los Alamos National Lab<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Tuesday, March 24, 2015, 2:30-3:30 pm<br><br><b>Abstract:</b> <p><span style="font-family: Monaco; font-size: 13px;">One of the best known problem that a quantum computer is expected to solve more efficiently than a classical one is the simulation of quantum systems. While significant work has considered the case of discrete, finite dimensional quantum systems, the study of fast quantum simulation methods for continuous-variable systems has only received little attention. In this talk, I will present quantum methods to simulate the time evolution of two quantum systems, namely the quantum harmonic oscillator and the quantum particle in a quartic potential. Our methods are based on well-known product formulas for approximating the evolution and result in superpolynomial and polynomial quantum speedups, respectively. I will also present efficient quantum algorithms to prepare the eigenstates of the quantum harmonic oscillator that can be used to compute spectral properties and may be of independent interest. Generalizations and connections between our results and the so-called fractional Fourier transform, which is a generalization of the Fourier transform used in signal analysis, will also be discussed.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9102015-02-13T22:19:20-05:002015-04-08T15:48:53-04:00https://talks.cs.umd.edu/talks/910Holographic quantum error-correcting codes: Toy models for the AdS/CFT correspondence<a href="http://www.its.caltech.edu/~rouge/">Beni Yoshida - Caltech</a><br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Wednesday, May 6, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 14px; line-height: 22px;">We propose a family of exactly solvable toy models for the AdS/CFT correspondence based on a novel construction of quantum error-correcting codes with a tensor network structure. Our building block is a special type of tensor with maximal entanglement along any bipartition, which gives rise to an exact isometry from bulk operators to boundary operators. The entire tensor network is a quantum error-correcting code, where the bulk and boundary degrees of freedom may be identified as logical and physical degrees of freedom respectively. These models capture key features of entanglement in the AdS/CFT correspondence; in particular, the Ryu-Takayanagi formula and the negativity of tripartite information are obeyed exactly in many cases. That bulk logical operators can be represented on multiple boundary regions mimics the Rindler-wedge reconstruction of boundary operators from bulk operators, realizing explicitly the quantum error-correcting features of AdS/CFT.</span></p>
<p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 14px; line-height: 22px;">This is a joint work with Daniel Harlow, Fernando Pastawski and John Preskill.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9112015-02-13T22:25:12-05:002015-04-27T16:03:06-04:00https://talks.cs.umd.edu/talks/911Quantum Computation and the Computational Complexity of Quantum Field TheoryKeith Lee - University of Toronto<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, April 29, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p>Quantum field theory provides the framework for the Standard Model of particle physics and plays a key role in physics. However, calculations are generally computationally complex and limited to weak interaction strengths. I'll describe polynomial-time quantum algorithms for computing relativistic scattering amplitudes in both scalar and fermionic quantum field theories. The algorithms achieve exponential speedup over known classical methods. One of the motivations for this work comes from computational complexity theory. Ultimately, one wishes to know what is the computational power of our universe. Studying such quantum algorithms probes whether a universal quantum computer is powerful enough to represent quantum field theory; in other words, is quantum field theory in BQP? Conversely, one can ask whether quantum field theory can represent a universal quantum computer; is quantum field theory BQP-hard? We have shown that massive phi^4 theory can implement universal quantum computation and is thus BQP-complete.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9182015-02-18T15:16:41-05:002015-06-15T14:09:30-04:00https://talks.cs.umd.edu/talks/918Quantum error correction for topological quantum systems(No abstract yet)<br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9212015-02-18T22:49:46-05:002015-02-23T10:46:22-05:00https://talks.cs.umd.edu/talks/921Quantum circuit optimization via matroid partitioningDmitri Maslov - NSF<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">2115 Computer and Space Sciences Building (CSS)</a><br>Monday, February 23, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <div style="font-family: Monaco; font-size: 12.8000001907349px;">In this talk I will give a broad overview of the topics I am interested in and was working on, and then concentrate on one recent result. Specifically, I will discuss an approach to the optimization of quantum Clifford+T circuits. The algorithm works in two stages: first, it efficiently (in polynomial time) optimizes {CNOT ,T} circuits with performance guarantee (optimally), and secondly, it is modified to handle Hadamard gates. The overall algorithm remains efficient while optimizing circuits over the complete fault-tolerant library {H, CNOT, T} = {{H, P=T^2, CNOT}, T} = {Clifford, T}, however, optimality may no longer be guaranteed. I will report the results of testing the practical performance of this algorithm using benchmarks. To illustrate the efficiency, a constant T-depth implementation of GF multiplication was discovered, whereas the best known circuits developed by humans had linear (and since more recently, logarithmic) T-depth. </div>
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<div style="font-family: Monaco; font-size: 12.8000001907349px;">No background beyond basic understanding of quantum computing and quantum circuit concepts is necessary.</div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9292015-02-24T13:02:39-05:002015-05-05T11:07:56-04:00https://talks.cs.umd.edu/talks/929Quantum conditional mutual information and approximate Markov chains<a href="http://perso.ens-lyon.fr/omar.fawzi/">Omar Fawzi - ENS Lyon</a><br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, May 13, 2015, 2:00-4:00 pm<br><br><b>Abstract:</b> <p><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">The Shannon and von Neumann entropies quantify the uncertainty in a</span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">system. They are operationally motivated by natural information</span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">processing tasks such as compression, channel coding or randomness </span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">extraction. In addition to characterizing the fundamental rates at </span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">which such tasks can be performed, their additivity properties make </span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">them a very valuable tool in applications ranging from complexity </span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">theory to many-body systems.</span><br style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;"><br style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;"><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">A difficulty that arises when dealing with quantum systems is the </span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">operational meaning of quantum observers, or the way to interpret </span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">conditional entropies. A particularly interesting quantity is the </span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">mutual information between two systems conditioned on a third quantum </span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">system. What notion of conditional independence does this quantity </span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">measure? After an overview of some of the applications of the </span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">conditional mutual information, I will show how the quantum </span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">conditional mutual information can be related to the task of local </span><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">recovery.</span><br style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;"><br style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;"><span style="font-family: UICTFontTextStyleBody; font-size: 17px; -webkit-text-size-adjust: auto;">Based on joint work with Renato Renner arXiv:1410.0664.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9512015-03-11T13:47:58-04:002015-03-23T15:35:52-04:00https://talks.cs.umd.edu/talks/951Efficient quantum learning of deep Boltzmann machinesGuoming Wang - University of Waterloo<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, April 1, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p style="font-family: Monaco; font-size: 13px;"><span>In recent years, deep learning has achieved great success in many areas of artificial intelligence, such as computer vision, speech recognition, natural language processing, etc. Its central idea is to build a hierarchy of successively more abstract representations of data (e.g. image, audio, text) by using a neural network with many layers. Training such a deep neural network, however, can be very time-consuming. In this talk, we will investigate whether quantum computing can make this process more efficient. We will focus on deep Boltzmann machine (DBM), an interesting deep model that has many theoretical merits but has been impractical for large-scale problems due to the difficulty of its training and inference. We will present a quantum-walk-based algorithm for preparing a coherent version of the Gibbs state of any given DBM. </span>This algorithm allows us to quickly estimate the gradient of the log-likelihood function, and thus to find a locally optimal solution to the DBM learning problem<span>. We will also present a quantum algorithm for evaluating the generative performance of any given DBM. Numerical results indicate that our algorithms learn better models than existing classical algorithms based on mean-field variational inference and Markov chain Monte Carlo method</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9602015-03-19T23:42:08-04:002015-04-08T15:48:14-04:00https://talks.cs.umd.edu/talks/960Quantum Gibbs samplers<a href="http://fernandobrandao.org">Fernando Brandao - Microsoft Research and University College London</a><br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, April 15, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <div style="font-family: Monaco; font-size: 13px;">In this talk I’ll present recent results relating the time of preparation of thermal states by quantum Gibbs samplers, the analogue of classical metropolis sampling. In particular I will connect the efficiency of quantum Gibbs samplers to the static properties of the thermal state, in particular whether it has a finite correlation length.</div>
<div style="font-family: Monaco; font-size: 13px;"><br>The goal is to generalize to the quantum case a sequence of beautiful works—by Stroock, Zergalinski, Martinelli and others—in mathematical physics and statistical mechanics showing the equivalence of mixing in time (fast convergence of the Glauber dynamics) to mixing in space (finite correlation length in the Gibbs state) for classical models.</div>
<div style="font-family: Monaco; font-size: 13px;"><br>The talk will be based on joint work with Michael Kastoryano.</div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9842015-04-01T16:59:13-04:002015-06-02T13:58:50-04:00https://talks.cs.umd.edu/talks/984Approximate span programs<a href="http://www.its.caltech.edu/~sjeffery/">Stacey Jeffery - Caltech</a><br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, June 10, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="color: #282828; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px;">Span programs are a model of computation that completely characterize quantum query complexity, and have also been used in some cases to get upper bounds on quantum time complexity. Any span program can be converted to a quantum algorithm that, given an input x, decides whether x is "accepted" by the span program, or "rejected" by the span program.</span><br style="color: #282828; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px;"><br style="color: #282828; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px;"><span style="color: #282828; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px;">We consider more general ways of using this model to design quantum algorithms, by relaxing the notion of which inputs are accepted and which inputs rejected by a particular span program. We describe two new types of algorithms that can be constructed from any span program. The first type of algorithm "approximately" evaluates the span program: given an input to the span program, it decides if the input is close to being accepted or far from being accepted. This allows span programs to be used in a natural way to solve property-testing-type problems. The second type of algorithm estimates the span program witness size of an input. </span><br style="color: #282828; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px;"><br style="color: #282828; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px;"><span style="color: #282828; font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px;">This talk is based on joint work with Tsuyoshi Ito.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9922015-04-03T16:01:47-04:002015-04-03T16:02:04-04:00https://talks.cs.umd.edu/talks/992Preconditioned quantum linear system algorithmDave Clader - APL<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, May 27, 2015, 2:00-4:00 pm<br><br><b>Abstract:</b> <p><span style="font-family: 'Lucida Grande', helvetica, arial, verdana, sans-serif; font-size: 14px; line-height: 20.15999984741211px;">We describe a quantum algorithm that generalizes the quantum linear system algorithm [Harrow et al., Phys. Rev. Lett. 103, 150502 (2009)] to arbitrary problem specifications. We develop a state preparation routine that can initialize generic states, show how simple ancilla measurements can be used to calculate many quantities of interest, and integrate a quantum-compatible preconditioner that greatly expands the number of problems that can achieve exponential speedup over classical linear systems solvers. To demonstrate the algorithm's applicability, we show how it can be used to compute the electromagnetic scattering cross section of an arbitrary target exponentially faster than the best classical algorithm.</span></p>
<p><span style="font-family: 'Lucida Grande', helvetica, arial, verdana, sans-serif; font-size: 14px; line-height: 20.15999984741211px;">Based on joint work with </span><span style="font-family: 'Lucida Grande', helvetica, arial, verdana, sans-serif; font-size: 14px; line-height: 20.15999984741211px;"><span style="font-family: 'Lucida Grande', helvetica, arial, verdana, sans-serif; font-size: 14px; line-height: 20.15999984741211px;">B. C. Jacobs and C. R. Sprouse.</span></span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/9962015-04-09T11:54:49-04:002015-05-15T09:57:11-04:00https://talks.cs.umd.edu/talks/996Query/witness trade-offs for quantum computations<a href="http://robinkothari.com">Robin Kothari - MIT</a><br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Tuesday, May 26, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p>In this talk I will talk about the power of quantum proofs in the framework of quantum query complexity. Specifically, I will discuss the trade-off between the number of queries to an input string and the number of qubits of a quantum proof needed to verify whether the input string possesses a property of interest, and how this trade-off is affected if we only require the algorithm to output the correct answer on a fraction of the inputs. This latter question relates to the power of quantum complexity classes with access to random oracles, and specifically to the conjecture that the complexity class QMA with access to a random oracle is no more powerful than the complexity class QAM.</p>
<p>This talk is based on ongoing work with Alessandro Cosentino and John Watrous from the University of Waterloo.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10052015-04-17T10:24:20-04:002015-04-17T10:24:20-04:00https://talks.cs.umd.edu/talks/1005Quantum property testing: A survey and one new resultRonald de Wolf - CWI and University of Amsterdam<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, July 8, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="color: #282828; font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 13px;">"Property testers" are algorithms that can efficiently handle very large amounts of data: given a large object that either has a certain property or is somehow “far” from having that property, a tester should efficiently distinguish between these two cases. In this talk we describe recent results obtained for quantum property testing. This area naturally falls into three parts. First, we may consider quantum testers for properties of classical objects. We survey the main examples known where quantum testers can be much more efficient than classical testers. We also describe one new result: a quantum algorithm for testing whether a given n-bit Boolean function f is a k-junta (i.e., depends on only k of the n input bits) using roughly sqrt{k} queries to f, which is quadratically faster than the best classical testers. Second, we may consider classical testers of quantum objects. This is the situation that arises for instance when one is trying to determine if untrusted quantum states or operations are what they are supposed to be, based only on classical input-output behavior. Finally, we may also consider quantum testers for properties of quantum objects, such as whether two states or unitaries are equal, whether a state is separable, etc. </span></p>
<p><span style="color: #282828; font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 13px;">This is based on joint work with Ashley Montanaro (survey arXiv:1310.2035) and with Andris Ambainis, Aleksanders Belovs, and Oded Regev (k-junta testing).</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10092015-04-20T10:33:00-04:002015-04-20T10:33:00-04:00https://talks.cs.umd.edu/talks/1009Topological color code and SPT phasesBeni Yoshida - Caltech<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, May 4, 2015, 3:00-4:00 pm<br><br><b>Abstract:</b> <p><span style="color: #282828; font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 13px;">We study (d−1)-dimensional excitations in the d-dimensional color code that are created by transversal application of the R_d phase operators on connected subregions of qubits. We find that such excitations are superpositions of electric charges and can be characterized by fixed-point wavefunctions of (d−1) dimensional bosonic SPT phases with (Z_2)^(\otimes d) symmetry. While these SPT excitations are localized on (d−1)-dimensional boundaries, their creation requires operations acting on all qubits inside the boundaries, reflecting the non-triviality of emerging SPT wavefunctions. Moreover, these SPT-excitations can be physically realized as transparent gapped domain walls which exchange excitations in the color code. Namely, in the three-dimensional color code, the domain wall, associated with the transversal R_3 operator, exchanges a magnetic flux and a composite of a magnetic flux and loop-like SPT excitation, revealing rich possibilities of boundaries in higher-dimensional TQFTs. We also find that magnetic fluxes and loop-like SPT excitations exhibit non-trivial three-loop braiding statistics in three dimensions as a result of the fact that the R_3 phase operator belongs to the third-level of the Clifford hierarchy. We believe that the connection between SPT excitations, fault-tolerant logical gates and gapped domain walls, established in this paper, can be generalized to a large class of topological quantum codes and TQFTs.</span></p>
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<p><span style="color: #282828; font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 13px;">Reference: arXiv:1503.07208 </span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10242015-04-28T12:13:08-04:002015-04-29T09:32:56-04:00https://talks.cs.umd.edu/talks/1024Advances in quantum algorithms for Hamiltonian simulationDominic Berry - Macquarie University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, July 1, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="color: #282828; font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 15px;">Hamiltonian simulation is a major potential application of quantum computers, because it enables predictions to be made for physical quantum systems, as well as providing a foundation for other quantum algorithms. Standard methods for Hamiltonian simulation involve product formulae, where the Hamiltonian evolution is a product of evolutions for a series of short times. We have developed a range of advanced algorithms with greatly improved performance. One method is to compress product formulae, which gives an exponential improvement in some parameters. A crucial part of this is an oblivious form of amplitude amplification, which allows the steps of this procedure to be performed deterministically. This also enables us to perform evolution based on a truncated Taylor series. Another approach is to use a quantum walk; using oblivious amplitude amplification we are able to perform a superposition of different numbers of steps of the walk, providing greatly improved performance.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10332015-05-05T15:34:39-04:002015-05-05T15:34:39-04:00https://talks.cs.umd.edu/talks/1033Quantum complexity and circuit obfuscationBill Fefferman - Maryland<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, May 27, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 14px; line-height: 22px;">How powerful are quantum computers? Despite the prevailing belief that quantum computers are more powerful than their classical counterparts, this remains a conjecture backed by little formal evidence. Shor's algorithm, for instance, gives an example of a problem (factoring), which can be solved efficiently on a quantum computer with no known efficient classical algorithm. Factoring however, is unlikely to be NP-hard, meaning that few unexpected formal consequences would arise, should such a classical algorithm be discovered. Could it then be the case that any quantum algorithm can be simulated efficiently classically? Likewise, could it be the case that quantum computers can quickly solve problems much harder than factoring? In particular, what classical computational resources do we need to solve the hardest problem that has an efficient quantum algorithm? In this seminar, we address these questions and give an overview of recent research proving that quantum computers can sample from distributions that cannot be sampled efficiently by classical computers. We further utilize these results to discuss the feasibility of quantum circuit obfuscation-- a powerful primitive with many applications to cryptography. We show that some of the most desirable variants of quantum obfuscation procedures are impossible to achieve. Despite this, there are other variants that are not able to prove impossible, and even constructions of candidate quantum circuit obfuscators. We survey these results, and give new, quantum applications of these more limited obfuscators. (Based on joint work with Chris Umans (Caltech) and Gorjan Alagic (Copenhagen).)</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10372015-05-14T16:32:19-04:002015-05-14T16:32:19-04:00https://talks.cs.umd.edu/talks/1037Dynamics after quantum quench in long-range field theoriesMohammad Ali Rajabpour - Fluminense Federal University, Brazil<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Monday, June 8, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <div style="color: #282828; font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 15px;">In this talk I will first introduce classical and quantum long-range Ising models and their field theory counterparts. I will show that in particular regimes these systems can be described with simple free non-local field theories with dispersion relation $\omega(k)=|k|^{\alpha/2}$. Having this motivation in mind I will first study many quantum aspects of free non-local field theories such as: the entanglement entropy, dynamics of local operators and entanglement entropy after quantum quenches. Then in particular cases I will also present some results regarding interacting field theories.</div>
<div style="color: #282828; font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 15px;"> </div>
<div style="color: #282828; font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 15px;">1: M. A. Rajabpour, S. Sotiriadis, Phys. Rev. B 91, 045131 (2015)</div>
<div style="color: #282828; font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 15px;">2: M. Ghasemi Nezhadhaghighi, M. A. Rajabpour, EPL, 100 (2012) 60011 and Phys. Rev. B 88, 045426 (2013) and Phys. Rev. B 90, 205438 (2014)</div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10442015-05-27T15:48:41-04:002015-05-27T15:48:41-04:00https://talks.cs.umd.edu/talks/1044Estimating outcome probabilities of quantum circuits using quasiprobabilitiesStephen Bartlett - University of Sydney<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Tuesday, June 23, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="color: #282828; font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 13.3333330154419px;">I'll present a method for estimating the probabilities of outcomes of a quantum circuit using Monte Carlo sampling techniques applied to a quasiprobability representation. This estimate converges to the true quantum probability at a rate determined by the total negativity in the circuit, using a measure of negativity based on the 1-norm of the quasiprobability. If the negativity grows at most polynomially in the size of the circuit, our estimator converges efficiently. These results highlight the role of negativity as a measure of non-classical resources in quantum computation.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10462015-06-10T12:33:32-04:002015-06-11T10:00:59-04:00https://talks.cs.umd.edu/talks/1046New Characterizations for Matrix Phi-Entropies, Poincare and Sobolev InequalitiesMin-Hsiu Hsieh - University of Technology, Sydney<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, July 29, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="color: #282828; font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 13.3333330154419px;">We derive new characterizations for the matrix Φ-entropies introduced in [Electron. J. Probab., 19(20): 1–30, 2014]. The fact that these new characterizations are a direct generalization of their corresponding equivalent statements for classical Φ-entropies provides additional justification to the original definition of matrix Φ-entropies. Moreover, these extra characterizations allow us to better understand the properties of matrix Φ-entropies, which are a powerful tool for unifying the study matrix concentration inequalities. We then move on to prove a Poincare inequality for these matrix Φ-entropies. Along the way, we also provide a new proof for the matrix Efron-Stein inequality. Finally, we derive a restricted logarithmic Sobolev inequality for matrix-valued functions defined on Boolean hypercubes. Our proof relies on the powerful matrix Bonami-Beckner inequality.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10572015-06-30T10:24:55-04:002015-06-30T10:24:55-04:00https://talks.cs.umd.edu/talks/1057Heralded quantum gates with integrated error detectionJohannes Borregaard - Harvard<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, July 9, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p>Individual atoms in optical cavities can provide an efficient interface between light and matter, something essential to quantum communication. Through the cavity field, quantum gates, such as the CNOT gate, can be realized between atoms trapped in the same cavity, which can be used in e.g. a quantum repeater to swap entanglement to large distances. Nonetheless, dissipation caused by cavity decay and spontaneous emission increases the experimental difficulty of realizing high quality gates in such a setup. In this talk, I will discuss how error detection can be employed to convert the dissipation errors, which would be present in a deterministic gate, into a non-unity success probability. Once successful, the resulting gate exhibit much higher fidelity than a similar deterministic gate. Furthermore, I will discuss how such a heralded gate can be directly incorporated in a quantum repeater to circumvent the demanding task of intermediate entanglement purification and thus greatly increase the distribution rate.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10592015-07-02T09:29:19-04:002015-07-02T09:29:19-04:00https://talks.cs.umd.edu/talks/1059Holographic Entanglement Entropy InequalitiesNing Bao - Caltech<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, August 26, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="font-family: 'Lucida Grande', helvetica, arial, verdana, sans-serif; font-size: 14.3999996185303px;">We initiate a systematic enumeration and classification of entropy inequalities satisfied by the Ryu-Takayanagi formula for conformal field theory states with smooth holographic dual geometries. For 2, 3, and 4 regions, we prove that the strong subadditivity and the monogamy of mutual information give the complete set of inequalities. This is in contrast to the situation for generic quantum systems, where a complete set of entropy inequalities is not known for 4 or more regions. We also find an infinite new family of inequalities applicable to 5 or more regions. The set of all holographic entropy inequalities bounds the phase space of Ryu-Takayanagi entropies, defining the holographic entropy cone. We characterize this entropy cone by reducing geometries to minimal graph models that encode the possible cutting and gluing relations of minimal surfaces. We find that, for a fixed number of regions, there are only finitely many independent entropy inequalities. To establish new holographic entropy inequalities, we introduce a combinatorial proof technique that may also be of independent interest in Riemannian geometry and graph theory.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10612015-07-06T13:45:06-04:002015-07-06T13:45:06-04:00https://talks.cs.umd.edu/talks/1061Coherent control of a many-body localized systemSoonwon Choi - Harvard<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, July 15, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="color: #282828; font-family: arial, helvetica, sans-serif; font-size: 15px;">We explore an approach to the coherent control and manipulation of quantum degrees of freedom in disordered, interacting systems in the many-body localized phase. Our approach leverages a number of unique features of many-body localization: a lack of thermalization, a locally gapped spectrum, and slow dephasing. We propose a protocol which enables one to efficiently prepare a many-body system into an effective eigenstate, encode quantum information, perform a universal set of gates, and ultimately readout the resulting state without the full microscopic knowledge of the Hamiltonian of the system. Finally, we provide an estimate for the fidelity of our protocol.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10632015-07-07T10:53:02-04:002015-07-09T16:24:29-04:00https://talks.cs.umd.edu/talks/1063High fidelity silicon semiconductor qubitsClement Wong - University of Wisconsin, Madison<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, July 16, 2015, 1:30-2:30 pm<br><br><b>Abstract:</b> <p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 13.838399887085px; line-height: 22px;">Semiconductor quantum dots in silicon are promising qubits because of long spin coherence times and their potential for scalability. However, whether qubits with fidelities above the threshold for quantum error correction can be achieved remains to be seen. We show theoretically that such high fidelities can be achieved in two types of electrically controlled double quantum dot qubits.</span></p>
<p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 13.838399887085px; line-height: 22px;">The singlet-triplet (ST) qubit, formed by the singlet and triplet spin states of 2 electrons in the presence of a magnetic fields, has been studied extensively in the zero angular momentum subspace. We propose a variant of this qubit that uses instead the polarized triplet state. Due to the presence of detuning sweet spots, this qubit is protected from charge noise, and possesses coherence times for both axes of rotations limited only by nuclear noise. The qubit fidelity is further improved when nuclear noise is reduced through isotopic purification, resulting in gate fidelities up to 99.9%. [Reference: C.H. Wong et. al. , Phys. Rev. B 92, 045403(2015)]</span></p>
<p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 13.838399887085px; line-height: 22px;">The "hybrid" quantum dot qubit is formed by three electrons in a double dot, and has practical advantages since it does not require magnetic fields and possesses GHz gate speeds. We analyze and optimize the the ac gate fidelities of this qubit, specifically focusing on decoherence caused by 1/f charge noise,. We find parameters that minimize the charge noise fluctuations of the qubit frequency, determine the optimal working points for ac gate operations that drive the detuning and tunnel coupling, and show that fidelities up to 99.5% can be achieved.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11322015-09-22T16:09:59-04:002015-09-22T16:09:59-04:00https://talks.cs.umd.edu/talks/1132Practical Bayesian TomographyChristopher Granade - University of Sydney<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, September 23, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 14px; line-height: 22px;">In recent years, Bayesian methods have been proposed as a solution to a wide range of issues in quantum state and process tomography. In this talk, we make these methods practical by solving three distinct problems: numerical intractability, a lack of informative prior distributions, and an inability to track time-dependent processes. Our approach allows for practical computation of point and region estimators for quantum states and channels, and allows tracking of time-dependent states.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10692015-07-29T00:11:30-04:002015-07-29T00:11:30-04:00https://talks.cs.umd.edu/talks/1069Completing Fermi's golden rule: the origin of transition rates in open systems<a href="http://www.quantum.umb.edu/Jacobs/">Kurt Jacobs - Army Research Laboratory</a><br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, August 5, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p>Fermi's golden rule is widely used, and the resulting transition rates are an important part of the thermal behaviour of open quantum systems. But this rule is curious because it is valid outside the regime in which it is derived: It is derived only for short times and for off-resonant transitions but works for all times and for resonant transitions. Here we show analytically that an interaction with a resonant, dense spectrum induces a rate equation for all times, giving essentially exact exponential decay in the appropriate regime. From this analysis we are able to extract the decay rate, which is indeed the rate of Fermi's golden rule (with a small correction), the short, non-Markovian time period before which the rate equation sets in, and determine the parameter regime required for this behavior. Our analysis provides the start of a more solid foundation on which to model thermal baths in terms of interactions with dense spectra.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10722015-08-11T10:15:01-04:002015-08-11T10:15:01-04:00https://talks.cs.umd.edu/talks/1072On the complexity of commuting quantum circuitsAdam Bouland - MIT<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, September 2, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 13.838399887085px; line-height: 22px;">Consider a model of quantum computation in which you require all the gates in your quantum circuit to commute. This is an extremely weak model of computation, as it seems unlikely to be capable of even universal classical computation. Surprisingly, in 2012, Bremner, Jozsa, and Shepherd showed that certain commuting circuits are difficult to simulate classically unless the polynomial hierarchy collapses. A natural question is if this sort of hardness result holds for other, more general, commuting circuits. In this work, we answer this question in the affirmative by showing that computations involving essentially *any* two-qubit commuting Hamiltonian are hard to simulate classically. Our proof makes use of Lie theory and properties of the exponential map on SL(2,C). This shows that generic commuting quantum circuits can perform computational tasks which are intractable for classical computers under plausible assumptions.</span></p>
<p><span style="color: #545454; font-family: Arial, Verdana, sans-serif; font-size: 13.838399887085px; line-height: 22px;">Based on joint work with Xue Zhang.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11832015-10-28T14:35:39-04:002015-10-28T15:45:27-04:00https://talks.cs.umd.edu/talks/1183Local Hamiltonians with no low energy statesLior Eldar - MIT<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, November 2, 2015, 3:00-4:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><span style="font-size: 10pt; font-family: Tahoma, sans-serif;">Quantum entanglement is usually considered very fragile, because quantum systems tend to interact with the environment, which means that even at very low temperature, multi-particle entanglement is very hard to maintain.</span><span style="font-size: 10pt; font-family: Tahoma, sans-serif;"> </span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family: Tahoma, sans-serif;">In this study, we place such "folklore" under scrutiny by constructing local Hamiltonians for which any quantum state whose energy w.r.t. the Hamiltonian is at most, say 0.05 of the total available energy, is highly entangled, in a precise sense: the minimal depth circuits for generating any low-energy states must have depth at least logarithmic in the number of qubits.</span><span style="font-size: 10pt; font-family: Tahoma, sans-serif;"> </span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family: Tahoma, sans-serif;">This, in particular, answers a conjecture by Freedman and Hastings called NLTS, and in a way, removes a significant obstacle to achieving a quantum analog of the PCP theorem - namely local Hamiltonians whose ground-energy is QMA-hard to approximate even to, say, 0.05 fractional additive error.</span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family: Tahoma, sans-serif;">In the talk, I'll assume no prior knowledge, so I'll describe the PCP and quantum PCP conjecture, the NLTS conjecture, and why previous works have actually indicated that it may be false.</span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family: Tahoma, sans-serif;">Without diving into too much details, I'll give a taste of the intuition behind our construction, and why quantum codes prove extremely useful in this case.</span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family: Tahoma, sans-serif;">Time allowing, I'll try to outline the next possible steps to be taken towards a more generalized and useful notion of "robust" quantum entanglement.</span></p>
<p class="MsoNormal"><span style="font-size: 10pt; font-family: Tahoma, sans-serif;">Joint work with Aram Harrow.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/10842015-08-26T10:10:00-04:002015-09-11T13:45:58-04:00https://talks.cs.umd.edu/talks/1084Generalized numerical ranges and Quantum error correctionChi-Kwong Li - College of William and Mary<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Friday, September 18, 2015, 2:00-3:00 pm<br><br><b>Abstract:</b> <p class="MsoPlainText">We describe how to use the generalized numerical ranges to help study problems in quantum error correction. Recent results and open problems will be mentioned.</p>
<p class="MsoPlainText"> </p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11222015-09-10T15:40:42-04:002015-09-11T09:51:14-04:00https://talks.cs.umd.edu/talks/1122Quantum walk speedup of backtracking algorithmsAshley Montanaro - University of Bristol<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, October 21, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="font-size: 11.0pt; font-family: 'Calibri','sans-serif'; ">In this talk I will discuss a general method to obtain quantum speedups of classical algorithms which are based on the technique of backtracking, a standard approach for solving constraint satisfaction problems (CSPs). Backtracking algorithms explore a tree whose vertices are partial solutions to a CSP in an attempt to find a complete solution. Assume there is a classical backtracking algorithm which finds a solution to a CSP on n variables, or outputs that none exists, and whose corresponding tree contains T vertices, each vertex corresponding to a test of a partial solution. I will present a bounded-error quantum algorithm which completes the same task using O(sqrt(T) n^(3/2) log n) tests. In particular, this quantum algorithm can be used to speed up the DPLL algorithm, which is the basis of many of the most efficient SAT solvers used in practice. The quantum algorithm is based on the use of a quantum walk algorithm of Belovs to search in the backtracking tree. I will also discuss how, for certain distributions on the inputs, the algorithm can lead to an average-case exponential speedup.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11232015-09-15T13:22:25-04:002015-09-15T13:22:25-04:00https://talks.cs.umd.edu/talks/1123Quantum Computing with Superconducting Resonator QuditsFrederick W. Strauch - Williams College<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, October 14, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoPlainText">Motivated by the phenomenal experimental progress in the coherent control of superconducting resonators, I will describe theoretical progress in how to perform full quantum computation using these devices operating with d (>2) dimensional quantum states (qudits). This progress includes multiple routes to single-qudit logic, entangled state synthesis, and two-qudit logic gates. I will also highlight the theoretical potential and experimental challenges of this approach to quantum logic, in relation to recent work on qudit nonlocality and the quantum Fourier transform.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11262015-09-17T10:01:15-04:002015-09-17T10:01:15-04:00https://talks.cs.umd.edu/talks/1126Quantum Correlations: Dimension Witnesses and Conic Formulations Jamie Sikora - Centre for Quantum Technologies, Singapore<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, October 7, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><span style="font-size: 10.0pt; font-family: 'URWPalladioL','serif';">In this talk, I will discuss correlations that can be generated by performing local measurements on bipartite quantum systems. I'll present an algebraic characterization of the set of quantum correlations which<span style="color: blue;"> </span>allows us to identify an easy-to-compute lower bound on the smallest Hilbert space dimension needed to generate a quantum correlation. I will then discuss some examples showing the tightness of our lower bound. Also, the algebraic characterization can be used to express the set of quantum correlations as the projection of an affine section of the cone of <em>completely positive semidefinite </em>matrices. Using this, we identify a semidefinite programming outer approximation to the set of quantum correlations which is contained in the first level of the Navascués, Pironio and Acín hierarchy, and a linear conic programming problem formulating exactly the quantum value of a nonlocal game. Time permitting, I will discuss other consequences of these conic formulations and some interesting special cases. </span></p>
<p> </p>
<p class="MsoNormal"><span style="font-size: 10.0pt; font-family: 'URWPalladioL','serif';">This talk is based on work with Antonios Varvitsiotis and Zhaohui Wei, arXiv:1507.00213 and arXiv:1506.07297. </span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11452015-10-01T10:23:21-04:002015-10-01T10:23:21-04:00https://talks.cs.umd.edu/talks/1145Resource efficient linear optics quantum computing using fibre-loop architecturesPeter Rohde - University of Technology, Sydney<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, October 12, 2015, 1:00-2:00 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Linear optics quantum computing is a promising candidate for the implementation of scalable quantum computing. However, it remains extremely technically challenging owing to the large number of optical elements that would be required for a large-scale device, potentially requiring millions of discrete elements. I present a substantially simplified scheme based on time-bin encoding, whereby only three optical elements are required, independent of the size of the computation. The simplicity arises from a fibre-loop architecture that allows the three optical elements to be reused, thereby reducing the number of required optical elements. I first show how this scheme can be used to implement boson-sampling, and then generalise it to implement universal quantum computing. Many of the required technologies for this scheme are available today, thus elementary demonstrations may be viable in the near future.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11462015-10-01T10:25:00-04:002015-10-01T10:25:00-04:00https://talks.cs.umd.edu/talks/1146Benchmarking quantum channels - the problem of regularizationDavid Elkouss - Universidad Complutense, Bristol<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, October 28, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">The classical capacity of a classical channel is found by maximizing the mutual information between the input and output of a single use of the channel. In contrast, the different capacities of quantum channels are obtained by the infinite regularization of particular entropic quantities. In this talk I will review our current understanding of the need for regularization. In particular, I will present some constructions that show that it is not possible to stop the regularization at some finite universal constant independent of the channel and still evaluate the capacity with arbitrary precision.</span><br style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;"><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">The talk will be based in arXiv:1408.5115 and arXiv:1502.05326.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11562015-10-07T13:30:06-04:002015-10-07T13:30:06-04:00https://talks.cs.umd.edu/talks/1156Analyzing Applications for Quantum Repeater NetworksRodney Van Meter - Keio University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Tuesday, October 20, 2015, 3:00-4:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">I divide the applications of quantum communications into three<br style="box-sizing: border-box;">categories: quantum cryptographic functions, quantum sensor networks, and distributed quantum computation. Some of these functions are drop-in replacements for existing, classical functionality, with additional, desirable characteristics. At least one of the most exciting is an entirely new capability brought by quantum computation.</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">In this short talk, I will discuss the demands that quantum key distribution, quantum Byzantine agreement, quantum interferometry, and blind quantum computation will make on large-scale quantum repeater networks. We will sketch out an evolutionary path that runs from a few Bell pairs per second through 1e11 Bell pairs per second, as repeater networks take on increasingly demanding applications.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12102015-11-13T14:13:52-05:002015-11-13T14:14:28-05:00https://talks.cs.umd.edu/talks/1210Chains of Josephson junctions: A resource for new physics and better devicesNicholas Grabon - JQI, QuICS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, November 20, 2015, 12:00-1:00 pm<br><br><b>Abstract:</b> <p><span style="font-size: 10pt; font-family: Arial, sans-serif; background: lime;">Free lunch served at <span style="z-index: 0;"><span class="aqj"><span style="z-index: -1;"><a href="https://exch.mail.umd.edu/owa/UrlBlockedError.aspx">11:45</a></span></span></span></span></p>
<p><span style="font-size: 10.0pt; font-family: 'Arial','sans-serif'; ">Superconducting qubits are shaping up to be promising candidates for a potential quantum computer. In addition to this specific value, the process of engineering such devices creates new elements for quantum circuits, reveals new paths for probing novel physics, and forces the development of techniques required to successfully work in the quantum regime. In this talk I will talk about one superconducting qubit in particular, fluxonium. I will describe how the development of Josephson junction chains led to very large inductance elements and in turn an opportunity to explore the ultrastrong coupling regime in the Jaynes-Cummings Hamiltonian. I will finish with a high level description of the experimental methods used to create these devices and view the interesting phenomena.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11842015-10-28T14:36:39-04:002015-10-28T14:36:39-04:00https://talks.cs.umd.edu/talks/1184A framework for approximating qubit unitariesMartin Roetteler - Microsoft<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, November 9, 2015, 1:00-2:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">We present an algorithm for efficiently approximating qubit unitaries over gate sets derived from totally definite quaternion algebras. The algorithm achieves ε-approximations using circuits of length O(log(1/ε)), which is asymptotically optimal. The algorithm achieves the same quality of approximation as previously-known algorithms for Clifford+T and a few other gate sets. Moreover, the algorithm to compile the efficient approximation is efficient as well: its running time is polynomial in O(log(1/ε)), conditional on a number-theoretic conjecture. Our algorithm works for a wide range of gate sets and might provide insight into what should constitute a "good" gate set for a fault-tolerant quantum computer.</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Based on joint work with Alex Bocharov, Vadym Kliuchnikov, and Jon Yard: <a style="box-sizing: border-box; color: #428bca; text-decoration: none; background-color: transparent;" href="http://arxiv.org/abs/1510.03888">http://arxiv.org/abs/1510.03888</a></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11852015-10-28T14:37:27-04:002015-11-16T16:56:46-05:00https://talks.cs.umd.edu/talks/1185A strong loophole-free test of local realismKrister Shalm - NIST<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Wednesday, November 18, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><span style="font-family: 'Times','serif'; ">Quantum mechanics is a statistical theory. It cannot with certainty predict the outcome of all single events, but instead it predicts probabilities of outcomes. This probabilistic nature of quantum theory is at odds with the determinism inherent in Newtonian physics and relativity, where outcomes can be exactly predicted given sufficient knowledge of a system. In 1935, Einstein, Podolsky, and Rosen wrote “While we have thus shown that the wave function does not provide a complete description of the physical reality, we left open the question of whether or not such a description exists. We believe, however, that such a theory is possible.” It was hoped that quantum theory could be augmented with extra “hidden” variables that determine the outcomes of all possible measurements (a principle known as realism). In 1964, John Bell showed that for such a theory to agree with the predictions of quantum mechanics, hidden variables in one location can instantly change values because of events happening in distant locations. This seemingly violates the locality principle from relativity, which says that objects cannot signal one another faster than the speed of light. Using Bell’s theorem it is possible to test whether reality is governed by local realism. </span><span style="font-family: 'Times','serif';"> </span></p>
<p class="MsoNormal"><span style="font-family: 'Times','serif'; ">In this talk I will discuss our statistically significant test of Bell’s inequalities. We have developed a high-quality source of entangled photons, high-efficiency single-photon detectors, and fast random number generators that are space-like separated from one another. Our experiment closes and addresses all of the major loopholes that are known to exist in Bell tests. This Bell test machine we are building will be used to certify randomness that is useful in a number of cryptographic and security protocols.</span></p>
<p class="MsoNormal"><span style="font-family: 'Times','serif'; ">Preprint available at: arXiv:1511.03189 [quant-ph]</span></p>
<br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11862015-10-28T14:38:00-04:002015-11-24T16:32:44-05:00https://talks.cs.umd.edu/talks/1186Error correction for quantum annealingDaniel Lidar - USC<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, December 2, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="font-size: 11.0pt; font-family: 'Calibri','sans-serif'; ">Just like all other quantum information processing methods, quantum annealing requires error correction in order to become scalable. I will report on our progress in developing and analyzing quantum annealing correction methods, and their implementation using the D-Wave Two processor at USC. </span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11872015-10-28T14:38:31-04:002015-12-01T09:15:58-05:00https://talks.cs.umd.edu/talks/1187Quantum Control & Quantum Error Correction with Superconducting CircuitsLiang Jiang - Yale<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, December 9, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="font-size: 12.0pt; font-family: 'Times New Roman','serif'; ">We have developed an efficient quantum control scheme that allows for arbitrary operations on a cavity mode using strongly dispersive qubit-cavity interaction and time-dependent drives [1,2]. In addition, we have discovered a new class of bosonic quantum error correcting codes, which can correct both cavity loss and dephasing errors. Our control scheme can readily be implemented using circuit QED systems, and extended for quantum error correction to protect information encoded in bosonic codes. Moreover, engineered dissipation can also implement holonomic quantum computation using superconducting circuits [3].<br> [1] Krastanov, et al., PRA 92, 040303 (2015)<br> [2] Heeres, et al., PRL 115, 137002 (2015)<br> [3] Albert, et al., arXiv: 1503.00194</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11882015-10-28T14:39:12-04:002015-10-28T14:39:12-04:00https://talks.cs.umd.edu/talks/1188Indra's wormholes: a mathematical tour of multiboundary wormholes and their entanglement structureShaun Maguire - Caltech<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, December 16, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Over the past decade, it has become increasingly clear that there are deep connections between high energy physics and quantum information, with entanglement serving as a bridge. The Ryu-Takayanagi conjecture is one of the seminal results which translates questions about the entanglement entropy of a CFT state to the task of calculating the lengths of minimal geodesics. These computations are especially tractable for 1+1d CFTs, where there are a variety of additional symmetries. These states are dual to 2+1d solutions of Einstein's equations via the AdS/CFT correspondence, but we will not go into much detail about this in this talk. Instead, we will provide an overview of these connections as they are relevant to quantum information theorists. More specifically, we will outline some of the surprising aspects of entanglement entropy in this family of states and what is known about how they are described by MERAs. This talk will include many computer-generated images.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11922015-10-29T16:36:57-04:002015-10-29T16:36:57-04:00https://talks.cs.umd.edu/talks/1192Building High Bandwidth Quantum Repeaters using Quantum Error CorrectionAndrew Glaudell - JQI, QuICS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, November 6, 2015, 12:00-1:00 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Quantum networks, with applications ranging from quantum key distribution to distributed quantum computing, ultimately require the sharing of entangled bell pairs between distant parties. The rate at which these pairs need to be generated depends on the application, but can approach and even exceed rates of one giga-entangled bit per second. To reach such rates at large separation distances, devices called quantum repeaters must be used to overcome photonic qubit errors and loss. In this talk, I will briefly discuss the different generations of proposed quantum repeaters and the application of quantum error correction within these devices. I will then analyze the performance that can be expected for these devices given both current quantum logic gate speed and fidelities and using optimal configurations, as well as what can be expected when the error rates of these devices improve.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/11932015-10-29T16:37:49-04:002015-10-29T16:37:49-04:00https://talks.cs.umd.edu/talks/1193A linear time algorithm for quantum 2-SATSevag Gharibian - Virginia Commonwealth University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, November 11, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">The Boolean constraint satisfaction problem 3-SAT is arguably the canonical NP-complete problem. In contrast, 2-SAT can not only be decided in polynomial time, but in fact in deterministic linear time. In 2006, Bravyi proposed a physically motivated generalization of k-SAT to the quantum setting, defining the problem "quantum k-SAT". He showed that quantum 2-SAT is also solvable in polynomial time on a classical computer, in particular in deterministic time O(n^4), assuming unit cost arithmetic over a field extension of the rational numbers, where n is number of variables. In this paper, we present an algorithm for quantum 2-SAT which runs in linear time, i.e. deterministic time O(n + m) for n and m the number of variables and clauses, respectively. Our approach exploits the transfer matrix techniques of Laumann et al. [QIC, 2010] used in the study of phase transitions for random quantum 2-SAT, and bears similarities with both the linear time 2-SAT algorithms of Even, Itai, and Shamir (based on backtracking) [SICOMP, 1976] and Aspvall, Plass, and Tarjan (based on strongly connected components) [IPL, 1979].</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">This talk is based on joint work with Niel de Beaudrap (University of Oxford).</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12252015-11-30T14:14:33-05:002015-12-17T09:14:29-05:00https://talks.cs.umd.edu/talks/1225Simulating quantum Systems with cellular automataPedro Costa - CBPF<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, February 1, 2016, 1:00-2:00 pm<br><br><b>Abstract:</b> <p class="MsoPlainText">Cellular automata-(CA) are computational structures spaciously and temporally discrete which were originally proposed by John von Neumann in the late 1940’s. They have the same computational power of Turing machines.This tool enables us to simulate a large number of different problems in distinct areas.</p>
<p class="MsoPlainText">After the discussion proposed by Richard Feynman about the efficiency of classical computers at simulating quantum systems, different quantum computational formalisms were proposed such as quantum circuits and quantum cellular automaton-(QCA), with the purpose of simulating quantum systems.</p>
<p class="MsoPlainText">In this seminar we will show different CA formalisms and see examples of its applications. In particular we will show how the random walk</p>
<p class="MsoPlainText">(RW) problem can be simulated by a CA. Its continuous limit can be achieved through the Chapman-Enskog expansion.</p>
<p class="MsoPlainText">Finally we will show, in analogous way, how the quantum walk (QW) is modelled by QCA and obtain its continouous limit.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12272015-12-01T15:33:56-05:002016-01-21T11:12:46-05:00https://talks.cs.umd.edu/talks/1227Random number generation from untrusted quantum devicesCarl Miller - U. Michigan<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, January 27, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p style="margin: 0in; margin-bottom: .0001pt;"><span style="font-size: 11.0pt; font-family: 'Calibri','sans-serif';">Is it possible to create a source of provable random numbers? If the answer to this question is "yes," it would be of importance in information security, where the safety of protocols such as RSA depends on the ability to generate random encryption keys. Bell inequality violations offer a potential solution: if a device exhibits a Bell inequality violation, then its outputs must have been computed by some quantum process and are therefore random. But, quantifying the amount of randomness that arises by this method is a difficult problem, and it motivates some intricate and beautiful mathematics.</span></p>
<p style="margin: 0in; margin-bottom: .0001pt;"><span style="font-size: 11.0pt; font-family: 'Calibri','sans-serif';"> </span></p>
<p style="margin: 0in; margin-bottom: .0001pt;"><span style="font-size: 11.0pt; font-family: 'Calibri','sans-serif';">In the talk I will present my work with Yaoyun Shi, which offered the first robust security proof for randomness expansion from Bell inequality violations. Any violation of the Clauser-Horne-Shimony-Holt inequality (as well as others) can be used to produce uniformly random bits. Our proofs, though they involve some mathematical heavy-lifting, ultimately reduce to two simple principles. The first is the notion of self-testing: for some Bell inequalities, a maximal violation allows us to deduce both the state and the measurements used. The second is a principle of measurement disturbance: if a measurement significantly alters a quantum state, then the outcome of the measurement must be random.</span></p>
<p style="margin: 0in; margin-bottom: .0001pt;"><span style="font-size: 11.0pt; font-family: 'Calibri','sans-serif';"> </span></p>
<p><span style="font-size: 11.0pt; font-family: 'Calibri','sans-serif'; ">References: arXiv:1411.6608 and arXiv:1402.0489.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12322015-12-03T16:59:40-05:002015-12-03T16:59:40-05:00https://talks.cs.umd.edu/talks/1232Postquantum steeringAna Belén Sainz - Bristol<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, December 17, 2015, 9:30 am-10:30 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">The discovery of postquantum nonlocality, i.e. the existence of nonlocal correlations stronger than any quantum correlations but nevertheless consistent with the no-signaling principle, has deepened our understanding of the foundations quantum theory. In this work, we investigate whether the phenomenon of Einstein-Podolsky-Rosen steering, a different form of quantum nonlocality, can also be generalized beyond quantum theory. While postquantum steering does not exist in the bipartite case, we prove its existence in the case of three observers. Importantly, we show that postquantum steering is a genuinely new phenomenon, fundamentally different from postquantum nonlocality. Our results provide new insight into the nonlocal correlations of multipartite quantum systems.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12352015-12-04T10:15:36-05:002015-12-04T10:15:36-05:00https://talks.cs.umd.edu/talks/1235Exponential Decay of Matrix \Phi-Entropies on Markov Semigroups with Applications to Dynamical Evolutions of Quantum EnsemblesHao-Chung Cheng - University of Technology, Sydney<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, January 20, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoPlainText">In the study of Markovian processes, one of the principal achievements is the equivalence between the \Phi-Sobolev inequalities and an exponential decrease of the\ Phi-entropies. In this work, we develop a framework of Markov semigroups on matrix-valued functions and generalize the above equivalence to the exponential decay of matrix \Phi-entropies. This result also specializes to spectral gap inequalities and modified logarithmic Sobolev inequalities in the random matrix setting. To establish the main result, we define a non-commutative generalization of the carre du champ operator, and prove a de Bruijn's identity for matrix-valued functions.</p>
<p class="MsoPlainText">The proposed Markov semigroups acting on matrix-valued functions have immediate applications in the characterization of the dynamical evolution of quantum ensembles. We consider two special cases of quantum unital channels, namely, the depolarizing channel and the phase-damping channel. In the former, since there exists a unique equilibrium state, we show that the matrix Phi-entropy of the resulting quantum ensemble decays exponentially as time goes on. Consequently, we obtain a stronger notion of monotonicity of the Holevo quantity - the Holevo quantity of the quantum ensemble decays exponentially in time and the convergence rate is determined by the modified log-Sobolev inequalities. However, in the latter, the matrix Phi-entropy of the quantum ensemble that undergoes the phase-damping Markovian evolution generally will not decay exponentially. This is because there are multiple equilibrium states for such a channel.</p>
<p><span style="font-size: 11.0pt; font-family: 'Calibri','sans-serif'; ">Finally, we also consider examples of statistical mixing of Markov semigroups on matrix-valued functions. We can explicitly calculate the convergence rate of a Markovian jump process defined on Boolean hypercubes, and provide upper bounds of the mixing time on these types of examples. (arXiv:1511.02627)</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12362015-12-07T11:46:36-05:002015-12-07T11:46:36-05:00https://talks.cs.umd.edu/talks/1236Topological quantum computation and compilationShawn Cui - UCSB<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, December 9, 2015, 1:30-2:30 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Topological quantum computation is a fault tolerant protocol for quantum computing using non-abelian topological phases of matter. Information is encoded in states of multi-quasiparticle excitations(anyons), and quantum gates are realized by braiding of anyons. The mathematical foundation of anyon systems is described by unitary modular tensor categories. We will show one can encode a qutrit in four anyons in the SU(2)_4 anyon system, and universal qutrit computation is achieved by braiding of anyons and one projective measurement which checks whether the total charge of two anyons is trivial. We will also give an algorithm to approximate an arbitrary quantum gate with the ones from the anyon system. The algorithm produces more efficient circuits than the Solovay-Kitaev algorithm. Time allowed, applications in quantum complexity classes will also be addressed.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12372015-12-07T15:00:48-05:002015-12-07T16:19:40-05:00https://talks.cs.umd.edu/talks/1237Electrically Controlled Qubits in SiliconEmily Pritchett - HRL<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, December 10, 2015, 1:30-2:30 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Quantum information processing aims to leverage the properties of quantum mechanics to manipulate information in ways that are not otherwise possible. This would enable, for example, quantum computers that could solve certain problems exponentially faster than a conventional supercomputer. One promising approach for building such a machine is to use gated silicon quantum dots. In the approach taken at HRL Laboratories, individual electrons are trapped in a gated potential well at the barrier of a Si/SiGe heterostructure. Spins on these electrons are compelling candidates for qubits due to their long coherence time, all-electrical control, and compatibility with conventional fabrication techniques. In this talk I will discuss the recent demonstration of all-electrical control of silicon-based qubits made from triple quantum dots in isotopically purified material, including methods to mitigate charge noise. The results indicate a strong future for silicon-based quantum technology.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12392015-12-08T09:38:38-05:002015-12-08T09:38:38-05:00https://talks.cs.umd.edu/talks/1239Quantum Simulation of a Wilson lattice gauge theoryChristine Muschik - Innsbruck<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">2115 Computer and Space Sciences Building (CSS)</a><br>Thursday, December 10, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p style="margin: 0px 0px 20px; padding: 0px; border: 0px; outline: 0px; vertical-align: baseline; font-stretch: inherit; font-size: 15px; line-height: 22.5px; font-family: proxima-nova, 'Helvetica Neue', Helvetica, Arial, sans-serif; color: #333333;">Gauge theories are the backbone of our current understanding of<br>fundamental interactions. While some of their aspects can be<br>understood using established perturbative techniques, the need for a<br>non-perturbative framework led to the lattice formulation of gauge<br>theories by Wilson in 1974. Since then, numerical simulations of<br>lattice gauge theories have celebrated success in a plethora of<br>equilibrium phenomena, such as the ab initio calculation of the<br>low-energy hadron spectrum. However, classical simulations of gauge<br>theories face a major challenge when addressing real-time dynamics,<br>which has hampered the full understanding of many physical phenomena<br>including the complex thermalization during heavy-ion collisions and<br>the dynamics of string breaking studied at high-intensity laser<br>facilities. Here, we report on the experimental realization of a U(1)<br>lattice gauge theory on a trapped ion quantum computer. By encoding<br>the gauge fields in asymmetric long-range interactions between the<br>fermions, we are able to realize a minimal instance of Wilson’s<br>version of quantum electrodynamics in (1+1)-dimensions, i.e., the<br>Schwinger model. We investigate its real-time dynamics following a<br>quantum quench from the vacuum state for a broad range of masses and<br>electric-field couplings. Further, we experimentally quantify the<br>entanglement generated during the dynamics, using the logarithmic<br>negativity, and show that it displays qualitatively different features<br>in different parameter regimes, which are already appreciable for the<br>modest system sizes under investigation.</p>
<p style="margin: 0px 0px 20px; padding: 0px; border: 0px; outline: 0px; vertical-align: baseline; font-stretch: inherit; font-size: 15px; line-height: 22.5px; font-family: proxima-nova, 'Helvetica Neue', Helvetica, Arial, sans-serif; color: #333333;">Joint work with M. Heyl, P. Hauke, M. Dalmonte, P. Zoller, E.<br>Martinez, D. Nigg, A. Erhard, P. Schindler, T. Monz, R. Blatt</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12422015-12-09T09:59:16-05:002015-12-09T09:59:16-05:00https://talks.cs.umd.edu/talks/1242Nonlocality with quantum inputs: fair-sampling assumption, post-selection, and the detection-loophole.Charles Lim - Oak Ridge<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, December 14, 2015, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p> </p>
<p class="MsoNormal"><span style=" color: black;">In this seminar, we look at how one can use certain properties of quantum physics to bypass the fair-sampling assumption commonly used in most practical Bell experiments. Our approach is based on an alternative nonlocality framework called “semi-quantum nonlocality”, where measurement instructions are represented by quantum inputs instead of classical inputs. A key feature of this framework is that all “entangled states are nonlocal”, in the sense that for any entangled state there is always a semi-quantum Bell inequality with which violation can be achieved. Building on this framework, we present a semi-quantum version of the CHSH inequality whose post-selected local bound is independent of the detection loss. We will then use this inequality as an example to illustrate how quantum inputs may be used to relax the fair-sampling assumption and hence close the detection-loophole. </span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12442015-12-14T09:22:17-05:002015-12-14T09:22:17-05:00https://talks.cs.umd.edu/talks/1244Random words, longest increasing subsequences, and quantum PCAJohn Wright - CMU<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, December 14, 2015, 3:00-4:00 pm<br><br><b>Abstract:</b> <p><span style="font-size: 9.5pt;">Suppose you have access to iid samples from an unknown probability distribution $p = (p_1, …, p_d)$ on $[d]$, and you want to learn or test something about it. For example, if one wants to estimate $p$ itself, then the empirical distribution will suffice when the number of samples, $n$, is $O(d/epsilon^2)$. In general, you can ask many more specific questions about $p$---Is it close to some known distribution $q$? Does it have high entropy? etc. etc.----and for many of these questions the optimal sample complexity has only been determined over the last $10$ years in the computer science literature.</span></p>
<p><span style="font-size: 9.5pt;">The natural quantum version of these problems involves being given samples of an unknown $d$-dimensional quantum mixed state $\rho$, which is a $d \times d$ PSD matrix with trace $1$. Many questions from learning and testing probability carry over naturally to this setting. In this talk, we will focus on the most basic of these questions: how many samples of $\rho$ are necessary to produce a good approximation of it? Our main result is an algorithm for learning $\rho$ with optimal sample complexity. Furthermore, in the case when $\rho$ is almost low-rank, we show how to perform PCA on it with optimal sample complexity.</span></p>
<p><span style="font-size: 9.5pt;">Surprisingly, we are able to reduce the analysis of our algorithm to questions dealing with the combinatorics of longest increasing subsequences (LISes) in random words. In particular, the main technical question we have to solve is this: given a random word $w \in [d]^n$, where each letter $w_i$ is drawn iid from some distribution $p$, what do we expect $\mathrm{LIS}(w)$ to be? Answering this question requires diversions into the RSK algorithm, representation theory of the symmetric group, the theory of symmetric polynomials, and many other interesting areas.</span></p>
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<p><span style="font-size: 9.5pt;">This is joint work with Ryan O'Donnell.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12462015-12-21T13:29:45-05:002016-01-04T09:35:11-05:00https://talks.cs.umd.edu/talks/1246Causal models for a quantum worldKatja Ried - IQC/Perimeter<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, January 7, 2016, 2:00-3:00 pm<br><br><b>Abstract:</b> <p style="margin-bottom: 14.2pt;">Quantum theory is a theory of information, imposing new -- and often counter-intuitive -- rules on how it can be acquired, processed and shared. To understand these rules, one can draw on the framework of causal Bayesian networks, which successfully addresses questions concerning knowledge, causation and inference in the context of classical statistics. The process of adapting classical causal models to accommodate quantum theory provides a new perspective on the fundamental differences between the two.</p>
<p style="margin-bottom: 14.2pt;">A central task in causal modeling is to characterize causal relations based solely on observed correlations. In the case of just two systems, we find that quantum coherence (eg entanglement) provides a distinct advantage for this problem, as it is known to do for other tasks such as cryptography and information processing. A linear optics experiment demonstrates this advantage in practice.</p>
<p style="margin-bottom: 14.2pt;">[Nat Phys 11, 414 (2015)]</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12472015-12-21T13:30:43-05:002016-01-05T10:25:37-05:00https://talks.cs.umd.edu/talks/1247Protected gates for topological quantum field theoriesMichael Beverland - Caltech<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, January 7, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><span style="font-size: 9.5pt;">We study restrictions on locality-preserving unitary logical gates for topological quantum codes in two spatial dimensions. A locality-preserving operation is one which maps local operators to local operators --- for example, a constant-depth quantum circuit of geometrically local gates, or evolution for a constant time governed by a geometrically-local bounded-strength Hamiltonian. Locality-preserving logical gates of topological codes are intrinsically fault tolerant because spatially localized errors remain localized, and hence sufficiently dilute errors remain correctable. By invoking general properties of two-dimensional topological field theories, we find that the locality-preserving logical gates are severely limited for codes which admit non-abelian anyons; in particular, there are no locality-preserving logical gates on the torus or the sphere with M punctures if the braiding of anyons is computationally universal. Furthermore, for Ising anyons on the M-punctured sphere, locality-preserving gates must be elements of the logical Pauli group. We derive these results by relating logical gates of a topological code to automorphisms of the Verlinde algebra of the corresponding anyon model, and by requiring the logical gates to be compatible with basis changes in the logical Hilbert space arising from local F-moves and the mapping class group. </span></p>
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<p class="MsoNormal"><span style="font-size: 9.5pt;">This is joint work with Oliver Buerschaper, Robert Koenig, Fernando Pastawski and Sumit Sijher.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12632016-01-14T13:51:09-05:002016-01-15T13:39:36-05:00https://talks.cs.umd.edu/talks/1263The limits of Matrix Product State ModelsMiguel Navascues - IQOQI-Vienna<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, February 10, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="font-family: Tahoma; font-size: 13px;">For the past twenty years, Tensor Network States (TNS) have been widely used to model the low energy sector of local Hamiltonians. Their success in doing so has led to the wide-held mantra that TNS of low bond dimension are the `only physical states' of natural condensed matter systems. However, given our experimental limitations to interact with such systems, it is not clear how this conjecture translates into any observable effect. In this Letter we give a first step in this direction by identifying particular operational features pertaining to all Matrix Product States (MPS), the class of TNS used to model non-critical one-dimensional spin chains. By exploiting two surprising structural constraints of MPS, we show how to systematically derive `bond dimension witnesses', or k-local operators whose expectation value allows us to lower bound the bond dimension of the underlying quantum state. We extend some of these results to the ansatz of Projected Entangled Pairs States (PEPS). As a bonus, we use our insight on the structure of MPS to derive some limitations on the use of MPS and PEPS for ground state energy computations.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12642016-01-14T13:51:52-05:002016-02-17T10:20:33-05:00https://talks.cs.umd.edu/talks/1264A Critical Examination of Coherence Resource TheoriesEric Chitambar - Southern Illinois University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, February 17, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Considerable work has recently been directed toward developing resource theories of quantum coherence. In this talk I will review the general structure of such resource theories, and I will argue that all currently proposed basis-dependent approaches to quantum coherence fail to be physically consistent. That is, the “free” or “incoherent” operations defined within these frameworks ultimately require the consumption of quantum coherence to be physically implemented. Despite this lack of consistence, I will explain how many of the currently proposed classes of incoherent operations still may be of physical interest. In particular, I will describe how entanglement and coherence can be related to each other through the tasks of resource dilution and resource distillation using local incoherent operations and classical communication.</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">This talk will cover joint work with Alex Streltsov et. al (arXiv:1507.08171), Min-Hsiu Hsieh (arXiv:1509.07458), and Gilad Gour (TBP).</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12652016-01-14T13:52:28-05:002016-02-12T14:45:24-05:00https://talks.cs.umd.edu/talks/1265Limitations of monogamy, Tsirelson-type bounds, and other semidefinite programs in quantum informationAram Harrow - MIT<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Friday, February 19, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="font-size: 12.0pt; font-family: 'Times New Roman','serif'; ">We introduce a new method for proving limitations on the ability of semidefinite programs (SDPs) to approximately solve optimization problems. We use this to show specifically that SDPs have limited ability to approximate two particularly important sets in quantum information theory: <br> 1. The set of separable (i.e. unentangled) states. <br> 2. The set of quantum correlations; i.e. conditional probability distributions achievable with local measurements on a shared entangled state. <br> In both cases no-go theorems were previously known based on computational assumptions such as the Exponential Time Hypothesis (ETH) which asserts that 3-SAT requires exponential time to solve. Our unconditional results achieve the same parameters as all of these previous results (for separable states) or as some of the previous results (for quantum correlations) and show that any SDPs which approximately solve either of these problems must have a number of variables which grows very quickly with problem size. <br> These results can be viewed as limitations on the monogamy principle, the PPT test, the ability of Tsirelson-type bounds to restrict quantum correlations, as well as the SDP hierarchies of Doherty-Parrilo-Spedalieri, Navascues-Pironio-Acin and Berta-Fawzi-Scholz. Indeed a wide range of past work in quantum information can be described as using an SDP on one of the above two problems and our results put broad limits on these lines of argument.<br> <br> This is joint work with Anand Natarajan and Xiaodi Wu.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12662016-01-14T13:53:02-05:002016-02-29T14:49:54-05:00https://talks.cs.umd.edu/talks/1266Compressed Sensing and QM: Recent Progress and State of the ArtDavid Gross - Cologne<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, March 9, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoPlainText">Every time the release button of a digital camera is pressed, several megabytes of raw data are recorded. But the size of a typical jpeg output file is only 10% of that. What a waste! Can't we design a process which records only the relevant 10% of the data to begin with?</p>
<p class="MsoPlainText">Compressed sensing is a young theory that achieves this trick for certain signals. There has been a fruitful exchange of ideas between this field and quantum physics: Mathematical methods from quantum information have found many applications in classical compressed data acquisition tasks. Conversely, compressed sensing ideas have advanced the theory of quantum state estimation. I will introduce the basics of the theory and outline where we stand with regards to quantum tomography applications. I will mention very recent results in uncertainty quantification, as well as applications of the diamond norm and the Clifford group in compressed sensing.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/12672016-01-14T13:53:32-05:002016-02-19T09:36:53-05:00https://talks.cs.umd.edu/talks/1267Fault-tolerant quantum computation in multi-qubit block codesTodd Brun - USC<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Friday, March 11, 2016, 2:00-3:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal">Fault-tolerant quantum computation (FTQC) can be done in principle: the threshold theorems show that, for sufficiently low error rates, it is possible to do quantum computations of arbitrary size. However, current schemes that allow such scaling--using concatenated or surface codes--require very large overhead to achieve quantum computation at realistic error rates. One approach to reduce this overhead is to encode multiple logical qubits in a single code block. By combining two different codes--one for storage and Clifford gates, one for non-Clifford gates--it is possible to do a universal set of encoded quantum gates by measuring logical operators and performing logical teleportation between code blocks. We analyze the performance of such schemes, and for a few choices of codes show numerically that one can do quite large quantum computations at moderate error rates. One of the key requirements of this scheme is the ability to prepare a set of different ancilla states reliably. We present a scheme for distillation of these ancilla states, and give evidence that it is possible to get good distillation rates with low residual errors. We also look at some variations of this scheme using different codes.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13282016-02-18T12:04:01-05:002016-02-18T12:04:01-05:00https://talks.cs.umd.edu/talks/1328Continuous wave single photon transistor based on a superconducting circuitDr. Oleksandr Kyriienko - Niels Bohr Institute<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, February 26, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial','sans-serif'; background: lime; ">Free lunch served at <span style="z-index: 0;"><span class="aqj"><span style="z-index: -1;"><a href="https://exch.mail.umd.edu/owa/UrlBlockedError.aspx">12:00</a></span></span></span></span></p>
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<p class="MsoNormal"><span style="font-size: 10.5pt; ">The development of an efficient single microwave photon detector represents the open challenge of circuit QED and typically relies on the time-variation of the control field. Searching for the simple ready-to-go setup, we propose a microwave frequency single photon transistor device which can operate under continuous wave probing. It can be realized using an impedance-matched system of a three level artificial atom coupled to two microwave cavities both connected to input/output waveguides. Using an additional classical drive for the upper transition, we find the parameter space where a single photon control pulse can be fully absorbed by hybridized excited states. This subsequently leads to series of quantum jumps in the upper manifold and appearance of a photon flux leaving the second cavity through a separate input/output port. The resulting device is robust to dephasing processes and possesses low dark count rate.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13552016-03-18T09:40:24-04:002016-03-18T09:40:24-04:00https://talks.cs.umd.edu/talks/1355Squeezed Light, Fast Light and Non-Linear OpticsDr. Brian Anderson - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, March 25, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial','sans-serif'; background: lime; ">Free lunch served at <span style="z-index: 0;"><span class="aqj"><span style="z-index: -1;"><a href="https://exch.mail.umd.edu/owa/UrlBlockedError.aspx">12:00</a></span></span></span></span></p>
<p class="MsoNormal"><span style="font-size: 13.5pt; font-family: 'Times','serif'; ">We will discuss a variety of interesting phenomena that have been demonstrated in non-linear optics experiments. In non-linear optics (NLO), an atom’s response to an electric field is not necessarily only proportional to the electric field. The atomic response could be proportional to higher powers of the electric field, as well. We have used a particular NLO process, called Four-Wave Mixing, to generate light with uncertainty distributions that are ‘squeezed’, and send pulses of light (but not information) faster than c. I will give an introduction in non-linear optics and quantum optics before discussing the results of recent experiments where we generate squeezed light and fast light.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13122016-02-03T12:39:16-05:002016-02-03T12:39:16-05:00https://talks.cs.umd.edu/talks/1312Is Brooklyn Expaning?Charles Clark - JQI<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, February 24, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Is Brooklyn expanding?</p>
<p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Alan Turing was fascinated by the possible variation of natural laws in time. There is just a hint of this in his paper, "Computing Machinery and Intelligence," the source of the famous phrase "the imitation game." The subject, long at the intersection of science and philosophy, has recently started to become of practical interest.</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Anyone can read Turing's paper, <a style="box-sizing: border-box; color: #428bca; text-decoration: none; background-color: transparent;" href="http://j.mp/1m1tat10n">http://j.mp/1m1tat10n</a> , which is freely available from its publisher. I recommend that all participants in this seminar do so beforehand.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13152016-02-04T15:11:45-05:002016-02-04T15:11:45-05:00https://talks.cs.umd.edu/talks/1315Quantum Annealing and its Digital ImplementationAlireza Shabani - Google<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, February 12, 2016, 12:00-1:00 pm<br><br><b>Abstract:</b> <p><span style="font-size: 10.0pt; font-family: 'Arial','sans-serif'; background: lime; ">Free lunch served at <span style="z-index: 0;"><span class="aqj"><span style="z-index: -1;"><a href="https://exch.mail.umd.edu/owa/UrlBlockedError.aspx">11:45</a></span></span></span></span></p>
<p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Quantum annealing (QA) is a heuristic method to solve optimization problems by utilizing quantum fluctuations to find a physical system in a near minimum-energy state. QA promises to computationally outperform classical algorithms for certain class of optimization problems. For problem sizes of practical interest, we cannot emulated QA on classical computers, instead we need a special quantum hardware to run QA. In this talk, I discuss a set of criteria for a computationally powerful quantum annealer device and describe our recent experiment on quantum circuit implementation of QA with superconducting qubits.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13222016-02-12T10:02:15-05:002016-02-16T16:23:52-05:00https://talks.cs.umd.edu/talks/1322Visualising two-qubit correlations using quantum steering ellipsoidsAntony Milne - Imperial College London<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, March 23, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal">The quantum steering ellipsoid formalism naturally extends the Bloch vector picture to provide a visualisation of two-qubit systems. If Alice and Bob share an entangled state then a local measurement by Bob steers Alice’s Bloch vector; given all possible measurements by Bob, the set of states to which Alice can be steered forms her steering ellipsoid inside the Bloch sphere. This gives us a novel geometric perspective on a number of quantum correlation measures such as entanglement, CHSH nonlocality and singlet fraction. In particular, by analysing a tripartite scenario we find that steering ellipsoid volumes obey a simple monogamy relation from which one can derive the well-known CKW (Coffman-Kundu-Wootters) inequality for the monogamy of entanglement. Remarkably, we can also use steering ellipsoids to derive some highly non-trivial results in classical Euclidean geometry, extending Euler's inequality for the circumradius and inradius of a triangle.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13252016-02-16T11:54:40-05:002016-02-18T10:12:32-05:00https://talks.cs.umd.edu/talks/1325Dynamical Localization of Coupled Relativistic Kicked Rotors. Efim Rozenbaum - JQI, CMTC<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, February 19, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><span style="font-size: 10.0pt; font-family: 'Arial','sans-serif'; background: lime; ">Free lunch served at <span style="z-index: 0;"><span class="aqj"><span style="z-index: -1;"><a href="https://exch.mail.umd.edu/owa/UrlBlockedError.aspx">12:00</a></span></span></span></span></p>
<p class="MsoNormal">A periodically-driven rotor is a prototypical model that exhibits a transition to chaos in the classical regime and dynamical localization (related to Anderson localization) in the quantum regime. In a recent preprint, <span style="font-family: 'Courier New';">arXiv:1506.05455</span>, Keser <em>et al.</em> considered a many-body generalization of coupled quantum kicked rotors, and showed that in the special integrable linear case, dynamical localization survives interactions. By analogy with many-body localization, the phenomenon was dubbed dynamical many-body localization. In the present work, we study a non-integrable model of coupled quantum relativistic kicked rotors. We find that the interacting model exhibits dynamical localization in certain parameter regimes, which arises due to a complicated interplay of genuine Anderson mechanism and limiting integrable dynamics. This analysis of coupled "kicked" Dirac equations indicates that dynamical few- and many-body localization can exist in non-integrable systems and as such represents a generic phenomenon. We also analyze quantum dynamics of the model, which for certain model's parameters exhibits highly unusual behavior - e.g., superballistic transport and peculiar spin dynamics.</p>
<p class="MsoNormal"> </p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13302016-02-19T10:42:06-05:002016-02-19T10:42:06-05:00https://talks.cs.umd.edu/talks/1330Quantum Algorithms and Circuits for Scientific ComputingStuart Hadfield - Columbia University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Friday, March 18, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal">Quantum algorithms for scientific computing require modules implementing fundamental functions, such as inverses, logarithms, trigonometric functions, and others. We require modules that have a well-controlled numerical error, that are uniformly scalable and reversible (unitary), and that can be implemented efficiently. Such modules are an important first step in the development of quantum libraries and standards for numerical computation.</p>
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<p class="MsoNormal">We present quantum algorithms and circuits for computing the square root, the natural logarithm, and arbitrary fractional powers. We provide performance guarantees in terms of their worst-case accuracy and cost. We further illustrate their performance by comparing to floating point implementations found in widely used numerical software.</p>
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<p class="MsoNormal">Joint work with Mihir K. Bhaskar, Anargyros Papageorgiou, and Iasonas Petras</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13382016-02-25T10:30:39-05:002016-02-25T10:30:39-05:00https://talks.cs.umd.edu/talks/1338Enabling fault tolerance with GSTKenneth Rudinger - Sandia National Laboratory<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, March 9, 2016, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="font-size: 10.5pt; font-family: Calibri, sans-serif;">The most powerful existing threshold theorems for fault tolerant quantum computing require one- and two-qubit gates that are within 1e-3 to 1e-4 (in diamond norm distance) of ideal. Certifying that an experimental qubit system achieves this threshold thus requires (1) characterizing the full process matrices of its gates, and (2), assigning reliable uncertainty regions. These requirements must be met for both one- and two-qubit gates, with errors that are small in the diamond norm distance. We demonstrate how to achieve all these desiderata using gate set tomography (GST). GST provides a full characterization (including diamond norm) that randomized benchmarking cannot, while avoiding process tomography's reliance on pre-calibrated operations. We show how to put very tight (<1e-4) error bars on any single-qubit gate diamond norm using GST, by incorporating data from long periodic circuits (gate sequences) akin to those that provide Heisenberg scaling in phase estimation. We also extend GST to two-qubit gates, by formalizing several aspects of GST to enable extensive optimizations, and discuss the tricks required to analyze two-qubit data. We benchmark two-qubit GST using simulated and trapped-ion data, achieving similarly tight (<1e-4) error bars on the diamond norm.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13402016-02-26T09:53:12-05:002016-02-26T09:53:12-05:00https://talks.cs.umd.edu/talks/1340Interplay of Dirac surface states and magnetic fluctuations in topological insulator heterostructuresHilary Hurst - JQI, CMTC<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, March 4, 2016, 12:45-1:45 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Free lunch served at 12:30 - This week only, we’ll be moving 30 minutes later, so lunch will be at 12:30 and the talk will be at 12:45 to accommodate the prospective student visit</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">We consider the proximity effect between Dirac states at the surface of a topological insulator and a ferromagnet with easy plane anisotropy, which is described by the XY-model and undergoes a Berezinskii-Kosterlitz-Thouless (BKT) phase transition driven by magnetic vortices. Classical mag- netic fluctuations interacting with the surface states of a topological insulator can be described by an effective gauge field. This model can be mapped onto the problem of Dirac fermions in a random magnetic field, however this analogy is only partial in the presence of electron-hole asymmetry or warping of the Dirac dispersion which results in screening of magnetic fluctuations. We show that this proximity coupling leads to anomalous transport behavior of the surface states near the BKT transition temperature. We also discuss topological insulator heterostructures as a platform for studying Dirac physics.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13462016-03-02T10:02:14-05:002016-03-04T11:26:15-05:00https://talks.cs.umd.edu/talks/1346Real-time dynamics of lattice gauge theories with a few-qubit quantum computerChristine Muschik - IQOQI-Innsbruck<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, March 10, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Gauge theories are fundamental to our understanding of interactions between the elementary constituents of matter as mediated by gauge bosons. However, computing the real-time dynamics in gauge theories is a notorious challenge for classical computational methods.<br style="box-sizing: border-box;">In the spirit of Feynman's vision of a quantum simulator, this has recently stimulated theoretical effort to devise schemes for simulating such theories on engineered quantum-mechanical devices, with the difficulty that gauge invariance and the associated local conservation laws (Gauss laws) need to be implemented.<br style="box-sizing: border-box;">We report the first experimental demonstration of a digital quantum simulation of a lattice gauge theory, by realising 1+1-dimensional quantum electrodynamics (Schwinger model) on a few-qubit trapped-ion quantum computer.</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">We are interested in the real-time evolution of the Schwinger mechanism, describing the instability of the bare vacuum due to quantum fluctuations, which manifests itself in the spontaneous creation of electron-positron pairs. To make efficient use of our quantum resources, we map the original problem to a spin model by eliminating the gauge fields in favour of exotic long-range interactions, which have a direct and efficient implementation on an ion trap architecture. We explore the Schwinger mechanism of particle-antiparticle generation by monitoring the mass production and the vacuum persistence amplitude. Moreover, we track the real-time evolution of entanglement in the system, which illustrates how particle creation and entanglement generation are directly related. Our work represents a first step towards quantum simulating high-energy theories with atomic physics experiments, the long-term vision being the extension to real-time quantum simulations of non-Abelian lattice gauge theories.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13482016-03-04T10:10:20-05:002016-03-04T10:10:29-05:00https://talks.cs.umd.edu/talks/1348Amperian pairing at the surface of topological insulatorsDr. Mehdi Kargarian - CMTC<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, March 11, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p>Free lunch served at <a href="https://exch.mail.umd.edu/owa/UrlBlockedError.aspx">12:00</a></p>
<p class="MsoNormal">The surface of a 3D topological insulator is described by a helical electron state with electron’s spin and momentum locked together. I will discuss that in the presence of ferromagnetic fluctuations the surface of a topological insulator is unstable towards a superconducting state with unusual pairing dubbed as Amperian pairings. The key idea is that the dynamical fluctuations of a ferromagnetic layer deposited on the surface of a topological insulators couple to the electrons as gauge fields. The transverse components of the magnetic gauge fields are unscreened and can mediate an effective interaction between electrons. What makes the mechanism of pairing to be of Amperian type is an attractive for electrons with momenta in the same directions. We show that this attractive interaction leads to p-wave pairing instability of the Fermi surface in Cooper channel.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13522016-03-07T15:48:21-05:002016-03-07T15:48:21-05:00https://talks.cs.umd.edu/talks/1352Adiabatic and time-independent universal computing on a 2D lattice with simple 2-qubit interactionsBarbara Terhal - Aachen University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, March 21, 2016, 1:00-2:00 pm<br><br><b>Abstract:</b> <div class="main-container container" style="box-sizing: border-box; margin-right: auto; margin-left: auto; padding-left: 15px; padding-right: 15px; width: 750px; overflow: auto;">
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<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility;">We show how to perform universal Hamiltonian and adiabatic computing using a time-independent Hamiltonian on a 2D grid describing a system of hopping particles which string together and interact to perform the computation. In this construction, the movement of one particle is controlled by the presence or absence of other particles, an effective quantum field effect transistor that allows the construction of controlled-NOT and controlled-rotation gates. The construction translates into a model for universal quantum computation with time-independent 2-qubit ZZ and XX+YY interactions on an (almost) planar grid. The effective Hamiltonian is arrived at by a single use of first-order perturbation theory avoiding the use of perturbation gadgets. The dynamics and spectral properties of the effective Hamiltonian can be fully determined.<br style="box-sizing: border-box;">Reference: S. Lloyd and B.M. Terhal, New Journal of Physics Vol. 18 (2016)</p>
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</div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13672016-03-25T13:48:38-04:002016-03-25T13:48:56-04:00https://talks.cs.umd.edu/talks/1367The computational complexity of calculating ground state energies to very high precisionDr. Cedric Lin - QuICS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, April 1, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p>Free lunch served at 12:00</p>
<p class="MsoNormal">Computational complexity theory studies the classification of computational problems according to the resources required to solve them. An important problem in quantum complexity theory is the local Hamiltonian problem - given a Hamiltonian composed of local terms, determine its ground state energy up to polynomial precision.</p>
<p class="MsoNormal">We characterize the complexity of a variant local Hamiltonian problem where exponential precision, instead of polynomial precision, is required. In particular, this problem exactly captures the difficulty of problems solvable in a reasonable amount of memory (but with no other constraints). Our result gives some evidence that projected entangled pair states (PEPS) are less computationally useful than general ground states.<br> <br> No knowledge of complexity theory will be assumed. Based on joint work with Bill Fefferman.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13722016-03-28T09:28:36-04:002016-03-28T09:28:36-04:00https://talks.cs.umd.edu/talks/1372Ph.D. Defense: Spectral graph theory with applications to quantum adiabatic optimizationMichael Jarret Baume - QuICS<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, March 28, 2016, 3:00-5:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Quantum adiabatic optimization (QAO) slowly varies an initial Hamiltonian with an easy-to-prepare ground-state to a final Hamiltonian whose ground-state encodes the solution to some optimization problem. Currently, little is known about the performance of QAO relative to classical optimization algorithms as we still lack strong analytic tools for analyzing its performance. In this talk, I will unify the problem of bounding the runtime of one such class of Hamiltonians -- so-called stoquastic Hamiltonians -- with questions about functions on graphs, heat diffusion, and classical sub-stochastic processes.</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Through a discussion of Cheeger inequalities, I will describe how the geometry of the ground-state is in one-to-one correspondence with the spectral gap of the corresponding Hamiltonian, and hence the runtime of both QAO and certain classical monte carlo techniques. Then, I will introduce new tools for bounding the spectral gap of stoquastic Hamiltonians and, by exploiting heat diffusion, show that one of these techniques also provides an optimal and previously unknown gap bound for a large class of graphs. Additionally, these methods suggest a novel, typically efficient classical simulation algorithm for QAO, sub-stochastic monte carlo.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13732016-03-28T09:29:31-04:002016-04-18T09:42:53-04:00https://talks.cs.umd.edu/talks/1373New separations in query complexityTroy Lee - Centre for Quantum Technologies, Singapore<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, April 20, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="font-size: 12.0pt; font-family: 'Times New Roman','serif'; ">For partial boolean functions, whose domain can be a subset of {0,1}^n, exponential separations are known between the number of queries a classical deterministic algorithm needs to compute a function and the number of queries a quantum algorithm needs. For a total boolean function f, whose domain is all of {0,1}^n, the situation is quite different: the quantum Q(f) and deterministic D(f) query complexities are always polynomially related, in fact D(f) = O(Q(f)^6). It was widely believed this relation was far from tight, as for 20 years the largest separation known between these two measures has been quadratic, witnessed by Grover's search algorithm. We exhibit a total boolean function with a 4th power separation between its quantum and deterministic query complexities. Interestingly, no new quantum algorithms are needed to achieve this separation---our quantum algorithm is based on Grover search and amplitude amplification.<br> <br> This is joint work with Andris Ambainis, Kaspars Balodis, Aleksandrs Belovs, Miklos Santha, and Juris Smotrovs.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13792016-04-01T09:48:13-04:002016-04-01T09:48:13-04:00https://talks.cs.umd.edu/talks/1379Metafluids and Parity-Time symmetric metamaterials: New optical material phases and phenomenaHadiseh Alaeian - IAP-Universität Bonn<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, April 13, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p>Textbook conceptions of light-matter interactions have been challenged by two recent material</p>
<p>advances - the development of metamaterials and the introduction of parity-time (PT)-symmetric</p>
<p>media. Metamaterials allow considerable control over the electric and magnetic fields of light, so</p>
<p>that the permittivity, permeability, and refractive index can be tuned throughout positive, negative,</p>
<p>and near-zero values. Metamaterials have enabled negative refraction, optical lensing below the</p>
<p>diffraction limit of light and invisibility cloaking. Complementarily, PT-symmetric media allow</p>
<p>control over electromagnetic field distributions in systems with balanced amounts of gain and loss,</p>
<p>so that light propagation can be asymmetric and directional. They have enabled lossless Talbot</p>
<p>revivals, unidirectional invisibility, and, combined with non-linear media, optical isolators.</p>
<p> </p>
<p>In this talk, I will elaborate on our efforts to make new types of optical and asymmetric</p>
<p>metamaterials, including liquid metamaterials and parity-time symmetric metamaterials. First, I</p>
<p>will describe our work on the design and demonstration of the first fluidic metamaterial. Rather</p>
<p>than relying on top-down fabrication techniques, we utilize protein directed assembly to synthesize</p>
<p>the constituent meta-molecules. Both individual meta-molecules and the bulk metamaterial</p>
<p>solution show a strong isotropic magnetic polarizability at optical frequencies. Our calculations</p>
<p>also indicate that these meta-molecules could enable negative refractive index liquids.</p>
<p>Then, I will introduce the new concept of Parity-Time symmetric nanophotonic materials. We</p>
<p>show how planar and coaxial metallo-dielectric structures with balanced inclusion of gain and loss</p>
<p>can be used for a variety of applications, including i) directional nanophotonic waveguides and</p>
<p>modulators; ii) directional metamaterials that have different refractive indices when viewed from</p>
<p>different sides; and iii) flat Veselago lenses which can overcome the Rayleigh diffraction limit of</p>
<p>conventional optical microscopy. Further, I will show how these meta-materials can be used to</p>
<p>control the emission of the electric, magnetic and chiral emitters and suggest a non-chiral platform</p>
<p>for enantio-specific identification and selection.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13812016-04-04T09:14:02-04:002016-04-04T09:14:02-04:00https://talks.cs.umd.edu/talks/1381Separations in query complexity using cheat sheetsRobin Kothari - MIT<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, May 9, 2016, 1:00-2:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal" style="margin-bottom: 12.0pt;"><span style="font-family: 'Arial','sans-serif';">We show a power 2.5 separation between bounded-error randomized and quantum query complexity for a total Boolean function, refuting the widely believed conjecture that the best such separation could only be quadratic (from Grover's algorithm). We also present a total function with a power 4 separation between quantum query complexity and approximate polynomial degree, showing severe limitations on the power of the polynomial method. Finally, we exhibit a total function with a quadratic gap between quantum query complexity and certificate complexity, which is optimal (up to log factors). These separations are shown using a new, general technique that we call the cheat sheet technique. The technique is based on a generic transformation that converts any (possibly partial) function into a new total function with desirable properties for showing separations. The framework also allows many known separations, including some recent breakthrough results of Ambainis et al., to be shown in a unified manner.</span></p>
<p><span style="font-size: 12.0pt; font-family: 'Arial','sans-serif'; ">This is joint work with Scott Aaronson and Shalev Ben-David</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13862016-04-06T14:10:05-04:002016-04-06T14:10:05-04:00https://talks.cs.umd.edu/talks/1386"Counterfactual'' communication protocolsLev Vaidman - Tel-Aviv University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, April 18, 2016, 3:00-4:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Counterfactual communication is communication without particles in the transmission channel. It is argued that an interaction-free measurement of the presence of opaque objects can be named `counterfactual', while proposed ``counterfactual'' measurements of the absence of such objects are not counterfactual. The quantum key distribution protocols which rely only on measurements of the presence of the object are counterfactual, but quantum direct communication protocols are not. Therefore, the name `counterfactual' is not appropriate for recent "counterfactual" protocols which transfer quantum states by quantum direct communication.</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">See <a style="box-sizing: border-box; color: #428bca; text-decoration: none; background-color: transparent;" href="http://carnap.umd.edu/philphysics/vaidmanvaxjo.pdf">http://carnap.umd.edu/philphysics/vaidmanvaxjo.pdf</a></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13892016-04-08T13:58:16-04:002016-04-08T13:58:24-04:00https://talks.cs.umd.edu/talks/1389Non-Markovian quantum friction of bright solitons in superfluidsDr. Dmitry Efimkin - JQI/CMTC<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, April 15, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p class="MsoNormal">Free lunch served at <a href="https://exch.mail.umd.edu/owa/UrlBlockedError.aspx">12:00</a></p>
<p class="MsoNormal">I will discuss the quantum dissipation of a bright soliton in a quasi-one-dimensional bosonic superfluid. I will argue that due to the integrability of the original problem, usual Ohmic friction proportional to a velocity is absent. It uncovers the non-Ohmic and non-Markovian friction, which can be interpreted as the backreaction of Bogoliubov quasiparticles inelastically scattered by an accelerating soliton, which represents an analogue of the Abraham-Lorentz force known in electrodynamic. </p>
<p class="MsoNormal">The talk is based on the recent work by Dmitry K. Efimkin, Johannes Hofmann and Victor Galitski -<a href="http://arxiv.org/abs/1512.07640">http://arxiv.org/abs/1512.07640</a></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/13962016-04-14T15:10:53-04:002016-04-14T15:10:53-04:00https://talks.cs.umd.edu/talks/1396Nanophotonic quantum interface for a single quantum dot spin qubitShuo Sun - JQI and IREAP<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, April 22, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><span style="font-size: 13.5pt; font-family: 'Times','serif'; ">Free lunch at 12:00</span></p>
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<p class="MsoNormal"><span style="font-size: 13.5pt; font-family: 'Times','serif'; ">The spin of a single electron confined in a quantum dot is a promising matter qubit for quantum information processing. This spin system possesses microsecond coherence time and allows picosecond timescale control using optical pulses. It is also embedded in a host semiconductor substrate that can be directly patterned to form compact integrated nanophotonic devices for photonic interfaces.</span></p>
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<p class="MsoNormal">In this talk, I will discuss our efforts to develop nanophotonic quantum interface for a single quantum dot spin qubit by strongly coupling the quantum dot to a photonic crystal cavity. I will firstly present a quantum switch between a quantum dot spin and a photon [1]. This switch realizes a transistor operating at the fundamental quantum limit, where in picoseconds timescales a single photon flips the orientation of a spin and the spin flips the polarization of the photon. This device could enable spin-photon entanglement [2], and thus plays an important role in integrated quantum networks involving multiple solid-state spin qubits interconnected by flying photons. Next I will show cavity enhanced optical readout of a quantum dot spin [3]. This approach utilizes the spin-dependent cavity reflectivity to determine the spin state, and is particularly suitable for qubits such as quantum dot spins that do not possess a good cycling transition for resonance fluorescence detection. I will conclude with a discussion of the future prospects of this technology for developing chip-integrated quantum information systems.</p>
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<p class="MsoNormal">[1] S. Sun et. al., Nature Nanotechnology advanced online publication (2016), doi:10.1038/nnano.2015.334.</p>
<p class="MsoNormal">[2] S. Sun and E. Waks, Physical Review A 90, 042322 (2014).</p>
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<p class="MsoNormal">[3] S. Sun and E. Waks, arXiv:1602.04367 (2016).</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14012016-04-18T09:57:12-04:002016-04-18T09:57:12-04:00https://talks.cs.umd.edu/talks/1401Momentum-Space Entanglement in Quantum Spin ChainsRex Lundgren - University of Texas at Austin <br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, April 27, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal">The momentum-space entanglement properties of several quantum spin chains are investigated. More specifically, we study the entanglement spectra, i.e. the set of eigenvalues of the reduced density matrix, between left-and right-moving particles in bosonic and fermionic formulations of quantum spin chains. We elaborate on how momentum-space entanglement spectra may support the numerical study of phase transitions and classify certain critical systems. We also investigate the momentum-space entanglement spectrum after a quantum quench and show that the momentum-space entanglement spectrum of the XXZ spin-half chain possesses many universal features both in equilibrium and after a quantum quench. </p>
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<p class="MsoNormal">References: Phys. Rev. Lett. 113, 256404 (2014), arXiv:1512.09030, arXiv:1603.01997</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14022016-04-18T10:01:16-04:002016-04-18T10:01:16-04:00https://talks.cs.umd.edu/talks/1402Universal Aspects of Quantum ThermalizationJim Garrison - University of California Santa Barbara <br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, June 1, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><span style="font-size: 10.0pt;">A very fundamental problem in quantum statistical mechanics involves whether--and how--an isolated quantum system will thermalize at long times. In quantum systems that do thermalize, the long-time expectation value of any "reasonable" operator will match its predicted value in the canonical ensemble. The Eigenstate Thermalization Hypothesis (ETH) posits that this thermalization occurs at the level of each individual energy eigenstate; in fact, any single eigenstate in a microcanonical energy window will predict the expectation values of such operators exactly. In recent work, we have identified, for a generic model system, precisely which operators satisfy ETH, as well as the limits to the information contained in a single eigenstate. Remarkably, our results strongly suggest that a single eigenstate can contain information about energy densities--and therefore temperatures--far away from the energy density of the eigenstate. After considering eigenstates, I will return to the more general case of time evolution following a quantum quench, and study which operators thermalize for typical initial states.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14082016-04-20T14:31:10-04:002016-04-20T14:31:10-04:00https://talks.cs.umd.edu/talks/1408Coherent three-photon process for creating metastable degenerate gasses of alkaline-earth-like atomsNeal Pisenti - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, April 29, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><span style="font-size: 9.0pt; font-family: 'Helvetica','sans-serif'; ">Free lunch served at 12:00</span></p>
<p class="MsoNormal"><span style="font-size: 9.0pt; font-family: 'Helvetica','sans-serif'; ">Creating degenerate gasses of metastable alkaline-earth-like (AE) atoms is an outstanding challenge due to large inelastic losses that prevent direct evaporation in the metastable state. However, obtaining degenerate samples in a metastable state is necessary for some quantum simulation proposals, and could help to advance atomic structure calculations or enable the study of quadrupolar physics. Here, we present a coherent three-photon process to transfer degenerate AE atoms from the ground state to either 3P2 or 3P0. Simulations of the optical bloch equations show theoretical transfer efficiencies of >~ 90% using reasonable experimental parameters in both strontium and ytterbium. We end with a discussion of the experimental challenges that need to be overcome to successfully realize such transfer efficiencies.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14252016-04-29T15:19:26-04:002016-04-29T15:19:26-04:00https://talks.cs.umd.edu/talks/1425Observation of prethermalization in trapped ion quantum spin chainsAaron Lee - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, May 6, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <div class="main-container container" style="box-sizing: border-box; margin-right: auto; margin-left: auto; padding-left: 15px; padding-right: 15px; width: 750px; overflow: auto;">
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<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility;">We present experimental investigations of quantum thermalization in a precisely controlled, interacting, 171Yb+ spin chain, with up to 22 ions. We quench the trapped ion spins in a quantum many-body Hamiltonian with single-atom addressing techniques and measure the long-term dynamics with single-site resolution. With a long-range transverse Ising model spin Hamiltonian, we observe emergence of an exotic prethermal phase in the quench dynamics. This non-trivial prethermal phase arises from an inhomogeneous effective potential landscape, due to a combination of the long-range interactions and the open boundary condition.</p>
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<div class="region region-footer" style="box-sizing: border-box;"> </div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14262016-05-03T09:39:47-04:002016-05-03T09:39:47-04:00https://talks.cs.umd.edu/talks/1426Monogamy of entanglement, no-cloning, and dissipative quantum state preparationPeter Johnson - Dartmouth<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, May 11, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <div class="main-container container" style="box-sizing: border-box; margin-right: auto; margin-left: auto; padding-left: 15px; padding-right: 15px; width: 750px; overflow: auto;">
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<p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility;">Monogamy of entanglement limits the distribution of quantum correlations in a many-body system. The no-cloning theorem states that quantum information cannot be copied. From quantum cryptography to quantum chemistry simulations, these principles govern our approach to quantum information processing and distinguish it from classical information processing. For the most part, mathematical investigations of the monogamy of entanglement and "no-cloning" have been independent. We make an in-depth comparison of these two principles, demonstrating their common origin and gaining insight from simple examples. Through this pursuit, we come upon an intriguing "parity difference" between causal and acausal quantum correlations (i.e. between quantum channels and states), which is not present in classical statistical mechanics. We then connect this investigation of quantum part-whole relationships to the task of dissipatively preparing a many-body entangled state using (quasi-)local resources. We determine conditions under which a target state is able to be the unique steady state of frustration-free quasi-local Liouvillian dynamics and discuss some illuminating examples.</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility;">References: JPA 48, 035307 (2015) and QIC 16, 0657 (2016)</p>
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<div class="region region-footer" style="box-sizing: border-box;"> </div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14292016-05-05T15:27:29-04:002016-05-05T15:27:29-04:00https://talks.cs.umd.edu/talks/1429Some thoughts about the Quantum Van Trees inequalityPablo Barberis Blostein - JQI (on leave for a year from National Autonomous University of Mexico)<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Thursday, May 12, 2016, 2:00-3:00 pm<br><br><b>Abstract:</b> <p>**PLEASE NOTE: This is a SPECIAL JQI SEMINAR - not a QuICS Seminar**</p>
<p class="MsoNormal">When a parameter of a quantum system is a random variable, the Quantum Van Trees inequality can be used to check if the combination of quantum measurement and estimator minimizes the error. In this talk we argue that, in general, the Quantum Van Trees inequality can not be saturated; when this happens it is not possible to use it to know if we are using the best measurement strategy. We propose a modification of the Quantum Van Trees inequality and discuss possible applications.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14302016-05-05T16:22:58-04:002016-05-05T16:23:14-04:00https://talks.cs.umd.edu/talks/1430Measuring entanglement spectrum in quantum many-body systemsGuanyu Zhu - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, May 13, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p class="MsoNormal"> Free lunch at 12:00</p>
<p class="MsoNormal">As first pointed out by Haldane and Li in the context of fractional quantum Hall effect, the full spectrum of the reduced density matrix of a subsystem, referred to as entanglement spectrum (ES), can serve as fingerprint of topological order (TO), which is itself a non-local feature and a pattern of long-range entanglement. The correspondence between ES and TO has been further explored since then and the importance of ES has been extended to the context of quantum criticality, symmetry-breaking phases, and most recently many-body localization. The ever increasing theoretical interests in ES hence urgently demands a feasible measurement protocol.</p>
<p class="MsoNormal">In this talk, we present a measurement protocol to access the entanglement spectrum of many-body states in experiments with cold atoms and cavity-QED. The measurement scheme is based on the ability to produce several copies of the state under investigation together with the possibility to perform a global swap gate between two copies conditional on the state of an auxiliary qubit or cavity photon mode. We show that this protocol can be implemented with state-of-the-art techniques in cold atom and circuit-QED experiments. In particular we show how the required conditional swap gate can be implemented with cold atoms using Rydberg interactions and with superconducting qubits using Jaynes-Cummings interactions. We illustrate this ideas on a simple (extended) Hubbard model where such a measurement protocol would reveal topological features of the Haldane phase. Our protocol can also be extended to other experimental systems, such as trapped ions.</p>
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<p class="MsoNormal">This talk is based on collaboration with Hannes Pichler, Alireza Seif, Eliot Kapit, Peter Zoller, and Mohammad Hafezi</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14312016-05-06T12:14:31-04:002016-05-06T12:14:31-04:00https://talks.cs.umd.edu/talks/1431Exploring new frontiers of quantum optical scienceMikhail Lukin - Harvard University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">2400 Computer and Space Sciences Building (CSS)</a><br>Monday, May 9, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: proxima-nova, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 15px; line-height: 22.5px;">*Please note: this is a JQI Seminar!*</span></p>
<p><span style="color: #333333; font-family: proxima-nova, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 15px; line-height: 22.5px;">We will discuss recent developments at a new scientific interface between quantum optics, nanoscience and quantum information science. Examples include the use of quantum optical techniques for manipulation of individual atom-like impurities at a nanoscale and for realization of hybrid systems combining atoms and atom-like systems with novel photonic devices. We will discuss how these techniques are used for probing non-equilibrium quantum dynamics in disordered many-body systems with long-range interactions, exploring quantum nonlinear optics, scaling up quantum networks and realizing new probes for condensed matter and biological systems.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14362016-05-13T10:04:00-04:002016-05-16T09:36:12-04:00https://talks.cs.umd.edu/talks/1436Quantum algorithms and field theory: problems and connections to quantum opticsKeith Lee - University of Toronto<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, May 18, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoPlainText">To give a reference point for the talk, I shall briefly summarize existing results regarding quantum computing for and from quantum field theory. I'll then describe some solved or open technical problems arising in this context, mentioning possible solutions of the latter. As will be apparent from this discussion, there exist various connections with topics in quantum optics and AMO physics. These include methods for state preparation, in particular adiabatic rapid passage, which I'll present in detail, as well as the issue of what one can do with a small quantum computer.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14372016-05-13T10:04:35-04:002016-05-13T10:04:35-04:00https://talks.cs.umd.edu/talks/1437Multiqubit Clifford groups are unitary 3-designsHuangjun Zhu - ITP, Cologne<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, May 19, 2016, 2:00-3:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">We show that the multiqubit (including qubit) Clifford group in any even prime power dimension is not only a unitary 2-design, but also a unitary 3-design. Moreover, it is a minimal unitary 3-design except for dimension 4. As an immediate consequence, any orbit of pure states of the multiqubit Clifford group forms a complex projective 3-design; in particular, the set of stabilizer states forms a 3-design. By contrast, the Clifford group in any odd prime power dimension is only a unitary 2-design. In addition, we show that no operator basis is covariant with respect to any group that is a unitary 3-design, thereby providing a simple explanation of why no discrete Wigner function is covariant with respect to the multiqubit Clifford group. This result is of interest to understanding the power of quantum computation. Finally, I will mention briefly the decomposition of the fourth tensor power of the Clifford group and construction of Clifford covariant 4-designs as well as potential applications in compressed sensing and quantum process tomography etc.</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;"><a style="box-sizing: border-box; color: #428bca; text-decoration: none; background-color: transparent;" href="http://arxiv.org/abs/1510.02619">http://arxiv.org/abs/1510.02619</a></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14382016-05-13T10:05:12-04:002016-05-23T09:26:33-04:00https://talks.cs.umd.edu/talks/1438Parallel repetition theorems for all entangled gamesHenry Yuen - MIT<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, June 8, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal">In complexity theory and cryptography, parallel repetition is a natural operation to reduce the error of a game or protocol without increasing the number of rounds. Raz's parallel repetition theorem is a cornerstone result in complexity theory showing that the value of two-player one round game, when repeated in parallel, decreases exponentially fast with the number of repetitions. Although the statement is intuitive, its analysis requires sophisticated techniques in information theory. </p>
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<p class="MsoNormal">A major open question in quantum complexity theory concerns whether an analogue of Raz's theorem holds when the players use quantum entanglement. Until recently, quantum parallel repetition theorems have only been established for special classes of games, but none were applicable to <em>all</em> games. In this talk, I'll discuss two new results on quantum parallel repetition theorems that apply to all games, including the first result that shows the entangled value of a parallel repeated game must converge to 0 for all games whose entangled value is less than 1.</p>
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<p class="MsoNormal">Joint work with Mohammad Bavarian and Thomas Vidick.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14392016-05-13T11:25:51-04:002016-05-13T11:25:51-04:00https://talks.cs.umd.edu/talks/1439Evidence for ferromagnetic instability in a repulsive Fermi gas of ultracold atomsFrancesco Scazza - INO-CNR and LENS - University of Florence (Italy)<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, May 20, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><span style="font-size: 9.0pt; font-family: 'Helvetica','sans-serif'; ">Free lunch served at <span style="font-size: 9.0pt; font-family: 'Helvetica','sans-serif'; "><span style="font-size: 9.0pt; font-family: 'Helvetica','sans-serif'; "><span style="font-size: 9.0pt; font-family: 'Helvetica','sans-serif'; "><a href="https://exch.mail.umd.edu/owa/UrlBlockedError.aspx">12:00</a></span></span></span></span></p>
<p class="MsoNormal"><span style="font-size: 9.0pt; font-family: 'Helvetica','sans-serif'; ">The fine control of interactions and optical trapping potentials in ultracold atomic ensembles provides unique opportunities to explore strongly correlated fermion phenomena, such as superfluidity and magnetism. In our experiment, we produce lithium-6 degenerate Fermi gases in the vicinity of a broad Feshbach resonance [1] and we subsequently superimpose to the samples a thin repulsive optical barrier. This technique enabled the study of the Josephson dynamics of fermionic superfluids flowing through an insulating barrier, spanning a wide range of interaction strengths across the BEC-BCS crossover [2]. More recently, by preparing two adjacent and fully spin-polarised domains at rest, we were able to study the magnetic properties of a repulsively interacting Fermi gas on the many-body upper energy branch. I'll report on the investigation of collective spin modes in this system and of the stability of the initial fully-polarized state. Diffusion measurements of the two approaching spin clouds reveal the temporary suppression of spin conductance above a critical interaction strength, closely connected to the concomitant observation of a spin-dipole mode softening, which points to the occurrence of a ferromagnetic instability. </span></p>
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<p class="MsoNormal"><span style="font-size: 9.0pt; font-family: 'Helvetica','sans-serif'; "><span style="font-size: 9.0pt; font-family: 'Helvetica','sans-serif'; ">[1] Burchianti, A. et al., <em>Efficient all-optical production of large 6Li quantum gases using D1 gray-molasses cooling</em>. Phys. Rev. A <strong>90</strong>, 043408 (2014)</span></span></p>
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<p class="MsoNormal"><span style="font-size: 9.0pt; font-family: 'Helvetica','sans-serif'; "><span style="font-size: 9.0pt; font-family: 'Helvetica','sans-serif'; ">[2] Valtolina, G. et al., <em>Josephson effect in fermionic superfluids across the BEC-BCS crossover</em>. Science <strong>350</strong>, 1505 (2015)</span></span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14432016-05-24T10:03:25-04:002016-07-11T09:33:20-04:00https://talks.cs.umd.edu/talks/1443Corrections for more accurate Hamiltonian simulationDominic Berry - Macquarie University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, July 20, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="font-size: 12pt; font-family: 'Times New Roman', serif;">Hamiltonian simulation is a very promising area of quantum algorithms where quantum computers can provide a dramatic speedup over classical computers. Until recently, all algorithms had poor scaling in the allowable error. New algorithms allow for complexity scaling logarithmically in the allowable error. One is based on implementing a Taylor series, and another is based on a superposition of different numbers of steps of a quantum walk. These algorithms are still somewhat suboptimal because the complexity has a multiplying factor that is logarithmic in the allowable error, whereas the lower bound has an additive factor. We have now developed general ways of correcting these algorithms, eliminating the multiplying factor, and giving an additive factor that is similar to the lower bound up to double-logarithmic factors.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14442016-05-24T10:03:56-04:002016-10-19T10:41:55-04:00https://talks.cs.umd.edu/talks/1444Relaxations of Graph IsomorphismLaura Mancinska - Bristol University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, October 26, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">The study of equivalence relations on mathematical structures is a vast theory embracing combinatorics, optimization, algebra, and mathematical logic. In this context, graph isomorphism and its hierarchy of relaxations constitute a central topic, not only for its elusive complexity, but also for its mathematical richness. We develop a framework which succeeds in capturing salient aspects of the relaxations of graph isomorphism with tools furnished by nonlocal games. This framework allows us to introduce quantum and non-signalling isomorphism. We show that non-signalling isomorphism is equivalent to fractional isomorphism as well as exhibit pairs of non-isomorphic graphs which are nevertheless quantum isomorphic. </div>
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<div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Our notion of quantum isomorphism can also be expressed in terms of a feasibility program over the recently introduced completely positive semidefinite cone. We can thus give relaxations of quantum isomorphism by considering the same program, but over the positive semidefinite or doubly nonnegative cones. The doubly nonnegative relaxation turns out to be equivalent to a previously defined notion based on coherent algebras associated to graphs. Interestingly, the main idea behind the proof of this purely classical result is based on Choi matrices and CPTP unital maps.</div>
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<div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Joint work with Albert Atserias, Robert Samal, David Roberson, Simone Severini, and Antonios Varvitsiotis.</div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14452016-05-27T09:27:42-04:002016-05-27T09:27:42-04:00https://talks.cs.umd.edu/talks/1445Entanglement Properties and Quantum Phase Transitions in Interacting Disordered One Dimensional SystemsRichard Berkovits - Bar-Ilan University, Israel<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Monday, June 27, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal">**This is a Special JQI Seminar**</p>
<p class="MsoNormal">Interacting disordered one-dimensional fermionic systems are an ideal test ground in order to investigate the interplay between properties of the entanglement and quantum phase transitions. Although 1D systems with uncorrelated disorder are always localized, they may exhibit a quantum phase transition to a metallic phase as function of disorder strength if the disorder is correlated (e.g., the Harper model). Once attractive interactions are considered, a transition to a metallic/superconducting phase is predicted. Even for repulsive interactions a transition at higher temperatures/excitation energies to a metallic regime is predicted. This is the celebrated many-body localization (MBL) transition, which has far reaching consequences on a wide range of subjects, from quantum information to biological processes. We will argue that entanglement properties are an ideal tool to investigate these phase transitions. We shall show that entanglement properties, such as the typical entanglement entropy, the statistics of the entanglement entropy, the statistics of the entanglement spectrum, are a powerful tool to characterize these phase transitions and may provide a way to characterize unconventional regions of the phase space such as the non-ergodic region of the MBL phase diagram.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14482016-06-06T12:17:58-04:002016-06-06T12:17:58-04:00https://talks.cs.umd.edu/talks/1448How to encrypt a quantum stateGorjan Alagic - University of Copenhagen<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, June 22, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <div class="main-container container" style="box-sizing: border-box; margin-right: auto; margin-left: auto; padding-left: 15px; padding-right: 15px; width: 750px; overflow: auto;">
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<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility;">Encryption of classical data is ubiquitous in everyday life. As quantum computation and communication gains wider use, encryption of quantum data is likely to become important as well. Until recently, the theory of quantum encryption was fairly limited, consisting primarily of the quantum analogue of the one-time pad. In this talk, I will discuss how to place quantum encryption on the same foundations as classical encryption, and how to translate many of the great achievements of classical encryption theory to the quantum setting. This includes quantum encryption schemes which satisfy a natural notion of semantic security against chosen-plaintext and non-adaptive chosen-ciphertext attacks. I will briefly mention applications of these schemes to impossibility proofs for quantum black-box obfuscation. Finally, I will discuss how to make these quantum encryption schemes immune to forgery, manipulation of ciphertexts, and adaptive chosen-ciphertext attacks. The talk is based on several joint works, with collaborators A. Broadbent, B. Fefferman, T. Gagliardoni, C. Schaffner and M. St. Jules.</p>
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</footer><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14552016-06-10T11:18:11-04:002016-07-25T09:46:06-04:00https://talks.cs.umd.edu/talks/1455Improved classical simulation of quantum circuits dominated by Clifford gatesDavid Gosset - IBM<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, July 27, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal">We present a new algorithm for classical simulation of quantum circuits over the Clifford+T gate set. The runtime of the algorithm is polynomial in the number of qubits and the number of Clifford gates in the circuit but exponential in the number of T gates. The exponential scaling is sufficiently mild that the algorithm can be used in practice to simulate medium-sized quantum circuits dominated by Clifford gates. The first demonstrations of fault-tolerant quantum circuits based on 2D topological codes are likely to be dominated by Clifford gates due to a high implementation cost associated with logical T gates. Thus our algorithm may serve as a verification tool for near-term quantum computers which cannot in practice be simulated by other means. To demonstrate the power of the new method, we performed a classical simulation of a hidden shift quantum algorithm with 40 qubits, a few hundred Clifford gates, and nearly 50 T gates.</p>
<p class="MsoNormal">This is joint work with Sergey Bravyi (PRL 116, 250501, 2016).</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14562016-06-17T10:27:58-04:002016-06-17T10:27:58-04:00https://talks.cs.umd.edu/talks/1456Self-organization of atoms coupled to a chiral reservoirZachary Eldredge - JQI, QuICS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, June 24, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><span style="font-size: 10.0pt; font-family: 'Arial','sans-serif'; background: lime; ">Free lunch served at <span style="z-index: 0;" tabindex="0"><span class="aqj"><span style="z-index: -1;"><a href="https://exch.mail.umd.edu/owa/UrlBlockedError.aspx">12:00</a></span></span></span></span></p>
<p><span style="font-size: 9.0pt; font-family: 'Arial','sans-serif'; ">Tightly confined modes of light, as in optical nanofibers or photonic crystal waveguides, can lead to large optical coupling in atomic systems, which mediates long-range interactions between atoms. These one-dimensional systems can naturally possess couplings that are asymmetric between modes propagating in different directions. Strong long-range interaction among atoms via these modes can drive them to a self-organized periodic distribution. In this talk, we examine the self-organizing behavior of atoms in one dimension coupled to a chiral reservoir. We determine the solution to the equations of motion in different parameter regimes, relative to both the detuning of the pump laser that initializes the atomic dipole-dipole interactions and the degree of reservoir chirality. In addition, we calculate possible experimental signatures such as reflectivity from self-organized atoms and motional sidebands.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14582016-07-06T09:44:03-04:002016-07-08T10:53:07-04:00https://talks.cs.umd.edu/talks/1458Rejection and Particle Filtering for Hamiltonian Learning Christopher Granade - University of Sydney<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, July 21, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal">Many tasks in quantum information rely on accurate knowledge of a system's Hamiltonian, including calibrating control, characterizing devices, and verifying quantum simulators. In this talk, we pose the problem of learning Hamiltonians as an instance of parameter estimation. We then solve this problem with Bayesian inference, and describe how rejection and particle filtering provide efficient numerical algorithms for learning Hamiltonians. Finally, we discuss how filtering can be combined with quantum resources to verify quantum systems beyond the reach of classical simulators.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15862016-10-19T11:17:10-04:002016-10-19T11:17:10-04:00https://talks.cs.umd.edu/talks/1586Partial breakdown of quantum thermalization in a Hubbard-like modelJim Garrison - JQI/QuICS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, October 28, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <div style="color: #222222; font-family: arial, sans-serif; font-size: 13px;"><em><span style="color: #000000; font-family: helvetica; font-size: 12px;">Lunch served at 12:00</span></em></div>
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<div style="color: #222222; font-family: arial, sans-serif; font-size: 13px;"><span style="color: #000000; font-family: helvetica; font-size: 12px;">We study the possible breakdown of quantum thermalization in a model of itinerant electrons on a one-dimensional chain without disorder, with both spin and charge degrees of freedom. The eigenstates of this model exhibit peculiar properties in the entanglement entropy, the apparent scaling of which is modified from a "volume law" to an "area law" after performing a partial, site-wise measurement on the system. These properties and others suggest that this model realizes a new, non-thermal phase of matter, known as a quantum disentangled liquid (QDL). The putative existence of this phase has striking implications for the foundations of quantum statistical mechanics.</span></div>
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<div style="color: #222222; font-family: arial, sans-serif; font-size: 13px;"><span style="color: #000000; font-family: helvetica; font-size: 12px;">The talk will be based on arXiv:1606.05650.</span></div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14872016-08-08T15:55:53-04:002016-08-15T09:26:38-04:00https://talks.cs.umd.edu/talks/1487What information theory teaches us on gravitational theoryHirosi Ooguri - Caltech<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, August 24, 2016, 2:00-3:00 pm<br><br><b>Abstract:</b> <p class="MsoPlainText">Positive energy theorems play a fundamental role in general relativity. Recently, we found a new class of positive energy theorems using information inequalities such as the positivity and monotonicity of the relative entropy.</p>
<p class="MsoPlainText">This and related applications of information theory are providing us new insights into gravitational theory.</p>
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<p class="MsoPlainText"> </p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14882016-08-08T15:56:34-04:002016-09-02T14:34:45-04:00https://talks.cs.umd.edu/talks/1488Quantum circuits for quantum operationsRoger Colbeck - University of York<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, September 7, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoPlainText">Every quantum gate can be decomposed into a sequence of single-qubit gates and controlled-NOTs. In many implementations, single-qubit gates are relatively 'cheap' to perform compared to C-NOTs (for instance, being less susceptible to noise), and hence it is desirable to minimize the number of C-NOT gates required to implement a circuit.</p>
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<p class="MsoPlainText">I will consider the task of constructing a generic isometry from m qubits to n qubits, while trying to minimize the number of C-NOT gates required. I will show a lower bound and then give an explicit gate decomposition that gets within a factor of about two of this bound.</p>
<p class="MsoPlainText">Through Stinespring's theorem this points to a C-NOT-efficient way to perform an arbitrary quantum operation. I will then discuss the case of quantum operations in more detail.</p>
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<p class="MsoPlainText"> </p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15052016-09-01T10:02:34-04:002016-09-01T10:02:43-04:00https://talks.cs.umd.edu/talks/1505Precision phase measurement using 2-mode squeezed statesPrasoon Gupta - JQI & NIST<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, September 9, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><span style="font-size: 10.0pt; font-family: 'Tahoma','sans-serif'; color: #073763; background: yellow; ">Free lunch served at 12:00pm</span></p>
<p class="MsoNormal"><span style="font-size: 10.0pt;">In my presentation, I will talk about precision length measurement using 2-mode squeezed states. I will discuss several different measurements that we can perform to beat the standard quantum limit (SQL) for phase measurement using our two-mode squeezed states. The talk will also contain some of our recent data that shows phase<br> measurements better than the SQL.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14902016-08-08T15:58:20-04:002016-10-28T13:25:40-04:00https://talks.cs.umd.edu/talks/1490Unifying gate-synthesis and magic state distillationEarl Campbell - University of Sheffield<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, November 9, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p style="margin: 1em 0px; padding: 0px; border: 0px; vertical-align: baseline; font-family: 'Lucida Grande', 'Lucida Sans Unicode', sans-serif; font-size: 13.008px;"><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">The leading paradigm for performing computation on quantum memories can be encapsulated as distill-then-synthesize. Initially, one performs several rounds of distillation to create high-fidelity magic states that provide one good T-gate, an essential quantum logic gate. Subsequently, gate synthesis intersperses many T-gates with Clifford gates to realise a desired circuit. We introduce a unified framework that implements one round of distillation and multi-qubit gate synthesis in a single step. Typically, our method uses the same number of T-gates as conventional synthesis, but with the added benefit of quadratic error suppression. Because of this, one less round of magic state distillation needs to be performed, leading to significant resource savings. This new perspective also led us towards new efficient algorithms for reducing the T-count in this family of multi-qubit circuits.</span></p>
<p style="margin: 1em 0px; padding: 0px; border: 0px; vertical-align: baseline; font-family: 'Lucida Grande', 'Lucida Sans Unicode', sans-serif; font-size: 13.008px;"><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">arXiv:1606.01906 and arXiv:1606.01904</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15152016-09-08T10:20:36-04:002016-09-16T08:36:44-04:00https://talks.cs.umd.edu/talks/1515Optimal Circuit-level Decoding of Surface CodesKrysta Svore - Microsoft Research<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, September 21, 2016, 2:00-3:00 pm<br><br><b>Abstract:</b> <p class="p1"><span class="s1">Surface codes exploit topological protection to increase error resilience in quantum computing devices and can in principle be implemented in existing hardware. They are one of the most promising candidates for active error correction, not least due to a polynomial time decoding algorithm which admits one of the highest predicted error thresholds. In this talk, we consider the dependence of this threshold on underlying assumptions including different noise models, and analyze the performance of a minimum weight perfect matching (MWPM) decoding compared to a mathematically optimal maximum likelihood (ML) decoding. Our ML algorithm tracks the success probabilities for all possible corrections over time and accounts for individual gate failure probabilities and error propagation due to the syndrome measurement circuit. </span></p>
<p> </p>
<p class="p1"><span class="s1">We present the true error threshold of an optimal circuit-level decoder, allowing us to draw conclusions about what kind of improvements are possible over standard MWPM and ideas for how to develop better decoders in the future.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15012016-08-30T09:57:07-04:002016-08-30T09:57:07-04:00https://talks.cs.umd.edu/talks/1501Entangling semiconductor spin qubits via the Coulomb interactionVanita Srinivasa - LPS, UMD<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, September 2, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p>*Free lunch served at 12:00*</p>
<p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Many proposed realizations of quantum information processing rely on rapid and robust entanglement of coherent qubits over a wide range of distances. While solid-state implementations based on electron spin qubits are potentially scalable, spin manipulation and coupling methods that take advantage of rapid control of the electron charge are often limited in range and remain susceptible to charge noise and relaxation. I will describe our theoretical approaches to addressing these challenges for spin qubits encoded in multiple electrons within systems of coupled quantum dots. We analyze a new regime for capacitive coupling of two-electron spin qubits that leads to high theoretical fidelities for entangling gates within silicon-based implementations in the presence of charge-based decoherence. We also show that the three-electron resonant exchange qubit provides both a protected operating point for rapid single-qubit manipulation and an electric dipole moment that enables multiple approaches for long-range entangling gates via a superconducting microwave resonator. These methods are inspired by techniques from circuit quantum electrodynamics, Hartmann-Hahn double resonance in NMR, and the Cirac-Zoller gate for trapped ions.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15022016-08-30T09:58:18-04:002016-08-30T09:58:18-04:00https://talks.cs.umd.edu/talks/1502Quantum-security of commitment schemes and hash functionsDominique Unruh - University of Tartu<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, September 21, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px; line-height: 20px;">Commitment schemes are a fundamental primitive in cryptography. Their security (more precisely the computational binding property) is closely tied to the notion of collision-resistance of hash functions. Classical definitions of binding and collision-resistance turn out too be weaker than expected when used in the quantum setting. We present strengthened notions (collapse-binding commitments and collapsing hash functions), explain why they are "better", and show how they be realized under standard assumptions.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15032016-08-30T09:59:12-04:002016-09-29T08:49:03-04:00https://talks.cs.umd.edu/talks/1503Qwire: A Core Language for Quantum CircuitsJennifer Paykin - U. Penn<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Friday, October 7, 2016, 3:00-4:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal">The QRAM model of quantum computing describes how a (hypothetical) quantum computer and a classical computer work together to produce sophisticated quantum algorithms. The classical computer handles the bulk of the computation and sends circuits to the quantum computer for execution. In this talk I will introduce the Qwire circuit language, which encodes circuits in a classical programming language of our choice and facilitates communication with an attached quantum computer. Qwire uses linear types to ensure that circuits are well-formed and has a sound operational semantics that reduces circuits to a small set of normal forms. In addition, the language is highly modular as it can be embedded into an arbitrary host language that treats circuits as first-class data.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/1">PL Reading Group</a> ⋅ <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/14692016-08-04T13:49:08-04:002016-08-31T11:47:46-04:00https://talks.cs.umd.edu/talks/1469Comparing classical and quantum complexity<a href="http://www.damtp.cam.ac.uk/people/r.jozsa/">Richard Jozsa - University of Cambridge</a><br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSI">2117 Computer Science Instructional Center (CSI)</a><br>Friday, September 23, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p>Issues of complexity are at the root of almost all theoretical aspects of quantum information science and correspondingly, concepts from theoretical computer science have provided a strikingly novel perspective on the foundations of quantum physics itself. For the theory of algorithms and computing, the formalism of 'classical simulation of quantum circuits' provides a mathematically precise tool for studying the rich relations between classical and quantum complexity. We will give an overview of this subject, indicating some elegant mathematical ingredients and implications for physics. Along the way we will mention some striking results for quantum Clifford circuits and matchgate circuits.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/2">CS Department</a> ⋅ <a href="https://talks.cs.umd.edu/lists/17">CS Research Seminar</a> ⋅ <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15092016-09-06T09:52:14-04:002016-09-06T09:52:14-04:00https://talks.cs.umd.edu/talks/1509Random tensor networks and holographic entanglement Sepehr Nezami - Stanford Institute for Theoretical Physics<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, September 19, 2016, 1:00-2:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><span style="font-size: 9.5pt; color: #454545;">Tensor networks provide a natural framework for exploring holographic dualities because their entanglement entropies automatically obey an area law. We study the holographic properties of networks of random tensors. We review several interesting structural features of the AdS/CFT correspondence and derive them in our model. Entropies of random tensor networks satisfy the Ryu-Takayanagi formula for all boundary regions, including corrections due to bulk entanglement. Our method is to interpret random tensor averages as the partition functions of classical ferromagnetic Ising models, so that the minimal surfaces of the Ryu-Takayanagi formula appear as domain walls. Increasing the entanglement of the bulk ultimately creates the analog of a black hole. The bulk-boundary correspondence defined by a random tensor network satisfies an appropriate quantum error correction property known as entanglement wedge reconstruction. We further study the multipartite entanglement structure of random stabilizer tensor networks and conclude by some remarks about the properties of entanglement entropy in holographic states.</span></p>
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<p class="MsoNormal"><span style="font-size: 9.5pt; color: #454545;">References: </span></p>
<p class="MsoNormal"><span style="font-size: 9.5pt; color: #454545;">1. Holographic Duality From Random Tensor Networks arXiv:1601.01694</span></p>
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<p class="MsoNormal"><span style="font-size: 9.5pt; color: #454545;">2. Multipartite Entanglement in Stabilizer Tensor Networks arXiv:1608.02595</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15142016-09-07T14:57:08-04:002016-09-07T14:57:08-04:00https://talks.cs.umd.edu/talks/1514Algorithms and Error Detection on a Programmable Ion Trap Quantum ComputerNorbert Linke - JQI, UMD Physics, NIST<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, September 30, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p>Free lunch served at 12:00 pm</p>
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<p class="MsoNormal"><span style="font-size: 9.5pt;">Trapped ions are a highly advanced platform for implementing quantum circuits. They provide standard pairs of magnetic field insensitive "atomic clock" states as qubits with unsurpassed coherence times and optical schemes for near-unity preparation and measurement, as well as strong Coulomb interactions to generate entanglement. </span></p>
<p class="MsoNormal"><span style="font-size: 9.5pt;">We present a modular architecture comprised of a chain of trapped 171Yb+ ions with individual Raman beam addressing and individual readout. We employ a pulse-shaping scheme [1] to use the transverse modes of motion in the chain to produce entangling gates between any qubit pair. This creates a fully connected system which can be configured to run any sequence of single- and two-qubit gates, making it in effect an arbitrarily programmable quantum computer [2] with a powerful native gate set. </span></p>
<p class="MsoNormal"><span style="font-size: 9.5pt;">To demonstrate the universality of this setup, we present experimental results from different quantum algorithms on five ions including the Deutsch-Jozsa algorithm and the Quantum Fourier Transform which we use to implement a Period Finding as well as a Phase Estimation protocol, the latter being a key ingredient in prime factorization. Additionally, recent results from an error detection experiment will be discussed which demonstrate fault-tolerance of a logical qubit. </span></p>
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<p class="MsoNormal"><span style="font-size: 9.5pt;">[1] T. Choi et al., Phys. Rev. Lett. 112, 19502 (2014)</span></p>
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<p class="MsoNormal"><span style="font-size: 9.5pt;">[2] S. Debnath et al., Nature 536, 63 (2016)</span></p>
<p class="MsoNormal"><span style="font-size: 9.5pt;">ACKNOWLEDGEMENTS</span></p>
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<p class="MsoNormal"><span style="font-size: 9.5pt;">This work is supported by the ARO with funding from the IARPA LogiQ program and the AFOSR MURI on Quantum Measurement and Verification.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15312016-09-15T09:43:41-04:002016-09-15T09:43:41-04:00https://talks.cs.umd.edu/talks/1531Optimal and Secure Measurement Protocols for Quantum Sensor NetworksZachary Eldredge - JQI and QuICS <br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, September 23, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p>FREE LUNCH SERVED AT 12:00</p>
<p class="MsoNormal"><span style="font-size: 10.0pt;">Studies of quantum metrology have shown that the use of many-body entangled states can lead to an enhancement in sensitivity when compared to product states. In this paper, we quantify the metrological advantage of entanglement in a setting where the quantity to be measured is a linear function of parameters coupled to each qubit individually. We first generalize the Heisenberg limit to the measurement of non-local observables in a quantum network, deriving a bound based on the multi-parameter quantum Fisher information. We then propose a protocol that can make use of GHZ states or spin-squeezed states, and show that in the case of GHZ states the procedure is optimal, i.e., it saturates our bound.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15322016-09-15T09:45:06-04:002016-09-15T09:45:06-04:00https://talks.cs.umd.edu/talks/1532Multi-Species Trapped Ion Modules for Large Scale Quantum ComputersVolkan Inlek - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, September 16, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <div class="main-container container" style="box-sizing: border-box; margin-right: auto; margin-left: auto; padding-left: 15px; padding-right: 15px; width: 750px; overflow: auto;">
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<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility;">Trapped atomic ions have proven to be among leading platforms on quantum information processing, with their long coherence times and high fidelity quantum operations. Scaling up to larger numbers of qubits is a remaining challenge; and a modular network of many ion traps with photonic interfaces is a promising solution. In this architecture, external fields can drive local entangling gates between qubits within a module. Connections throughout the network can be achieved via probabilistic photonic entanglement between qubits in different modules. If all ions are the same species, resonant light scattered by photonic connection qubits can be absorbed by neighboring memory qubits and corrupt the stored information. To address this issue, we have implemented co-trapping of two different atomic species in the same ion trap: 171Yb+ for quantum information storage and 138Ba+for intermodular connection. In this talk, I will present our experimental results towards realization of this multi-species modular network architecture.</p>
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</footer><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15332016-09-15T09:46:27-04:002016-09-15T09:46:27-04:00https://talks.cs.umd.edu/talks/1533Comparing classical and quantum complexityRichard Jozsa - University of Cambridge<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSI">2117 Computer Science Instructional Center (CSI)</a><br>Friday, September 23, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">CS Colloquium</span></p>
<p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">**NOTE: Building is COMPUTER SCIENCE INSTRUCTIONAL CENTER, not Computer and Space Science** </span></p>
<p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Issues of complexity are at the root of almost all theoretical aspects of quantum information science and correspondingly, concepts from theoretical computer science have provided a strikingly novel perspective on the foundations of quantum physics itself. For the theory of algorithms and computing, the formalism of 'classical simulation of quantum circuits' provides a mathematically precise tool for studying the rich relations between classical and quantum complexity. We will give an overview of this subject, indicating some elegant mathematical ingredients and implications for physics. Along the way we will mention some striking results for quantum Clifford circuits and matchgate circuits.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15642016-10-04T11:39:59-04:002016-10-04T14:45:26-04:00https://talks.cs.umd.edu/talks/1564Zero-knowledge proof systems for QMAFang Song - Portland State University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, October 12, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNormal">Zero-knowledge (ZK) proof systems are fundamental in modern cryptography. Prior work has established that all problems in NP admit classical zero-knowledge proof systems, and under reasonable hardness assumptions for quantum computations, these proof systems can be made secure against quantum attacks.</p>
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<p class="MsoNormal">In this talk, I will present our recent work that further generalizes these results in a quantum setting. We show that every problem in QMA admits a zero-knowledge proof system under a mild intractable assumption. Our QMA proof system is sound against arbitrary quantum provers, but only requires an honest prover to perform polynomial-time quantum computations, provided that it holds a quantum witness for a given instance of the QMA problem under consideration. I'll describe the main tools we develop to build the ZK proof systems: 1) a new variant of the QMA-complete local Hamiltonian problem in which the local terms are described by Clifford operations and standard basis measurements; and 2) a new quantum encoding scheme that provides authentication and transversal Clifford operations. </p>
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<p class="MsoNormal">Joint work with Anne Broadbent, Zhengfeng Ji, and John Watrous. <a href="https://arxiv.org/abs/1604.02804">https://arxiv.org/abs/1604.02804</a></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15602016-09-26T10:31:33-04:002016-09-26T10:31:33-04:00https://talks.cs.umd.edu/talks/1560Surface code error correction on a defective lattice Shota Nagayama et al.Rodney Van Meter - Keio University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, October 17, 2016, 2:00-3:00 pm<br><br><b>Abstract:</b> <p class="MsoPlainText">The yield of physical qubits fabricated in the laboratory is much lower than that of classical transistors in production semiconductor fabrication. Actual implementations of quantum computers will be susceptible to loss in the form of physically faulty qubits. Though these physical faults must negatively affect the computation, we can deal with them by adapting error correction schemes. In this paper We have simulated statically placed single-fault lattices and lattices with randomly placed faults at functional qubit yields of 80%, 90% and 95%, showing practical performance of a defective surface code by employing actual circuit constructions and realistic errors on every gate, including identity gates. We extend Stace et al.'s superplaquettes solution against dynamic losses for the surface code to handle static losses such as physically faulty qubits. The single-fault analysis shows that a static loss at the periphery of the lattice has less negative effect than a static loss at the center. The randomly-faulty analysis shows that 95% yield is good enough to build a large scale quantum computer. The local gate error rate threshold is <span style="font-family: 'Cambria Math','serif'; ">∼</span>0.3%, and a code distance of seven suppresses the residual error rate below the original error rate at p=0.1%. 90% yield is also good enough when we discard badly fabricated quantum computation chips, while 80% yield does not show enough error suppression even when discarding 90% of the chips. We evaluated several metrics for predicting chip performance, and found that the depth of the deepest stabilizer circuit in the lattice gave the strongest correlation with post-correction residual error rates. Our analysis will help with selecting usable quantum computation chips from among the pool of all fabricated chips.</p>
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<p class="MsoPlainText">Rodney Van Meter received a B.S. in engineering and applied science from the California Institute of Technology in 1986, an M.S. in computer engineering from the University of Southern California in 1991, and a Ph.D. in computer science from Keio University in 2006.</p>
<p class="MsoPlainText">He has held positions in both industry and academia in both the U.S. and Japan. His current research centers on quantum computer architecture and quantum networking. Other research interests include storage systems, networking, and post-Moore's Law computer architecture. He is now an Associate Professor of Environment and Information Studies at Keio University's Shonan Fujisawa Campus.</p>
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<p class="MsoPlainText">Dr. Van Meter is a member of AAAS, ACM, IEEE and IPSJ.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15622016-09-28T09:55:42-04:002016-09-28T09:55:42-04:00https://talks.cs.umd.edu/talks/1562A Landauer formulation of photon transport in driven systemsChiao-Hsuan Wang - UMD/JQI/QuICS <br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, October 7, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p class="MsoNormal"><em><span style="font-size: 9.5pt;">Free lunch served at 12:00</span></em></p>
<p class="MsoNormal"><span style="font-size: 9.5pt;">Understanding the behavior of light in non-equilibrium scenarios underpins much of quantum optics and optical physics. While lasers provide a severe example of a non-equilibrium problem, recent interests in the near-equilibrium physics of photon `gases', such as in Bose condensation of light or in attempts to make photonic quantum simulators, suggest one reexamine some near-equilibrium cases. Here we consider how a sinusoidal parametric coupling between two semi-infinite photonic transmission lines leads to the creation and flow of photons between the two lines. </span></p>
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<p class="MsoNormal"><span style="font-size: 9.5pt;">Our approach provides a photonic analogue to the Landauer transport formula, and using non-equilbrium Green's functions, we can extend it to the case of an interacting region between two photonic `leads' where the sinusoid frequency plays the role of a voltage bias. Crucially, we identify both the mathematical framework and the physical regime in which photonic transport is directly analogous to electronic transport, and regimes in which other new behavior such as two-mode squeezing can emerge.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15742016-10-05T10:59:38-04:002016-10-05T10:59:38-04:00https://talks.cs.umd.edu/talks/1574Nonlinear looped band structure of Bose-Einstein condensates in an optical latticeElizabeth Goldschmidt - US Army Research Laboratory<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, October 14, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p class="MsoNormal">We study experimentally the stability of excited, interacting states of bosons in a double-well optical lattice where the nonlinear interactions are expected to induce "swallowtail" looped band structure. By experimentally preparing different initial coherent states and observing their subsequent decay, we observe distinct decay rates in regimes where multi-valued looped band structure is expected. This qualitative agreement with a dynamic homogeneous Gross-Pitaevskii calculation is not, however, matched by a quantitative agreement for the stability of the excited loop states. I will discuss potential explanations for this discrepancy and further work on this phenomenon.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15782016-10-12T09:57:00-04:002016-10-12T09:57:00-04:00https://talks.cs.umd.edu/talks/1578What does the effective resistance of electrical circuits have to do with quantum algorithms?Shelby Kimmel - QuICS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, October 21, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><em><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Free lunch served at 12:00 pm</span></em></p>
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<p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">I will answer the question in the title. I will also describe a new quantum algorithm for Boolean formula evaluation and an improved analysis of an existing quantum algorithm for st-connectivity. Joint work with Stacey Jeffery. </span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15912016-10-26T13:19:46-04:002016-10-26T13:19:46-04:00https://talks.cs.umd.edu/talks/1591Patterned Complexity in Atomic ScatteringBrandon Ruzic - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, November 4, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><em><span style="color: #222222; font-family: arial, sans-serif; font-size: small;">Free lunch served at 12:00</span></em></p>
<p><span style="color: #222222; font-family: arial, sans-serif; font-size: small;">As the constituents of cold gaseous matter continue to grow in complexity, the necessity to understand their basic collision processes remains. Exotic atomic species like erbium and dysprosium have been cooled to ultracold temperatures, revealing a dense forest of chaotically distributed resonances, a much more complicated landscape than the broad, isolated resonances seen in alkali-atom systems. Nevertheless, broad resonances emerge from the chaos. These resonances correspond to special halo-like eigenstates, which seem to occur in a predictable pattern. In this talk, I will describe a simple and powerful quantum defect theory for atomic scattering, how this theory can simply describe chaotic collisions, and how this theory may illuminate the character of the halo-like eigenstates.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16032016-11-10T14:44:53-05:002016-11-22T08:48:39-05:00https://talks.cs.umd.edu/talks/1603What does the Moser-Tardos RESAMPLE algorithm do when it does not work?Mario Szegedy - Rutgers University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, November 30, 2016, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px;">The celebrated Lovasz Local Lemma (LLL) guarantees that locally sparse systems always have solutions, </span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px;">which one can also algorithmically find by the Moser-Tardos RESAMPLE algorithm. Among the major questions that remain open is that how far *beyond* Lovasz's condition can we expect that RESAMPLE still performs in polynomial (linear) expected running time? Stating the question correctly is a challenge already. For a solvable and fixed instance RESAMPLE always comes up with a solution, but the catch is that the number of steps may be very large. We have therefore looked at parameterized instance families and tried to identify phase transitions in terms of these parameters. Perhaps the biggest lesson we have learned is that if we want to see phase transition thresholds, i.e. identify parameter values where RESAMPLE ``stops working,'' we need to understand what happens when RESAMPLE does *not* work. We have noticed that in this case the algorithm settles at a metastable equilibrium (at least for the homogenous instances we have considered), a phenomenon mostly studied for physical systems. We demonstrate (and illustrate) many of </span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px;">the interesting findings on a simple Coin Chain (spin chain) model. Even for this simple model some major mysteries are remaining.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/15982016-11-03T11:32:17-04:002016-11-03T11:32:17-04:00https://talks.cs.umd.edu/talks/1598A supersonically expanding Bose-Einstein condensate: analogies to the expanding universe?Avinash Kumar - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, November 11, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><em><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;">Lunch served at</span></em><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;"> 12:00</span></p>
<p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;">In standard cosmology, the expansion of the early universe occurs at a speed larger than the speed of light. This expansion also impacts many of the quantum fields that exist inside our universe. Our experiment consisting of neutral $^{23}$Na Bose-Einstein condensate trapped in an all optical ring realizes the basic features of this expansion. Specifically, we demonstrate redshifting of phonons and a reheating effect that is similar to pre-heating after the inflation stage of the universe. We also observe spontaneous non-zero winding numbers appear in the ring after the expansion is complete. We predict the widths of the resulting winding number distributions using Monte Carlo simulations according to the geodesic rule. Our experimental data agrees well with our theory, with no tunable parameters.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16022016-11-10T09:47:47-05:002016-11-10T09:47:47-05:00https://talks.cs.umd.edu/talks/1602Trapped ions as a quantum spin glass annealerTobias Grass - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, November 18, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><em><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;">Lunch served at 12:00</span></em></p>
<p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;">Solving spin glass models is a complex, often NP-hard, task. In this talk, I will discuss a strategy to attack this problem using trapped ions as a flexible emulator of spin Hamiltonians. Studying its dynamics in a slowly decaying magnetic field, such system can be used as a quantum annealer which might be capable of solving hard optimization problems in polynomial time.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16092016-11-18T08:40:24-05:002016-11-28T08:51:21-05:00https://talks.cs.umd.edu/talks/1609A Classical Network Protocol to Support Distributed Quantum State TomographyTakafumi Oka - Keio University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, December 5, 2016, 3:00-4:00 pm<br><br><b>Abstract:</b> <div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">This research presents the design of a classical networking protocol that supports distributed quantum state tomography, which provides necessary information for quantum error correction to work properly.</div>
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<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Also, the main audience would be familiar with classical communication, but not with quantum physics, because the conference focuses on classical networking as a whole. Therefore the paper provides some of the backgrounds on quantum communication as well.</div>
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<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"><span style="box-sizing: border-box;">The paper of the same title is going to be presented at the QCIT (Quantum Communications and Information Technology) Workshop, held on </span><span class="aBn" style="box-sizing: border-box;" tabindex="0">Thursday, 8 December</span><span style="box-sizing: border-box;">, which is part of IEEE Global Communications Conference, a conference on classical networking.</span></div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16132016-11-28T08:43:20-05:002016-11-28T08:43:20-05:00https://talks.cs.umd.edu/talks/1613Shortcuts to quantum network routingEddie Schoute - QuICS and Qutech, Delft University of Technology, the Netherlands<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, December 2, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><em><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;">Lunch served at 12:00</span></em></p>
<p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;">A quantum network promises to enable long distance quantum communication and assemble small quantum devices into a large quantum computing cluster. Each network node can thereby be seen as a small quantum computer. Qubits can be sent over direct physical links connecting nearby quantum nodes, or by means of teleportation over pre-established entanglement amongst distant network nodes. Such pre-shared entanglement effectively forms a shortcut - a virtual quantum link - which can be used exactly once.</span><br style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;"><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;">We present an abstraction of a quantum network that allows ideas from computer science to be applied</span><br style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;"><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;">to the problem of routing qubits and managing entanglement in the network. Specifically, we consider a scenario in which each quantum network node can create EPR pairs with its immediate neighbors over a physical connection and perform entanglement swapping operations in order to create long distance virtual quantum links. We proceed to discuss the features unique to quantum networks that call for the development of new routing techniques. As an example, we present two simple hierarchical routing schemes for a quantum network of N nodes for a ring and sphere topology. For these topologies we present efficient routing algorithms requiring O(log N) qubits to be stored at each network node, O(polylog N) time and space to perform routing decisions, and O(log N) timesteps to replenish the virtual quantum links in a model of entanglement generation.</span><br style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;"><br style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;"><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px; white-space: pre-wrap;">Based on the paper: arXiv:1610.05238</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16182016-12-01T08:28:50-05:002016-12-01T08:28:50-05:00https://talks.cs.umd.edu/talks/1618Realizing quantum advantage without entanglement in single-photon statesAlejandra Marcela Maldonado Trapp - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, December 9, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><em><span style="font-size: 12.8px;">Lunch served at 12:00</span></em></div>
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<div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><span style="font-size: 12.8px;">Quantum Discord expresses quantum correlations beyond those associated with entanglement. Although its theory has been extensively studied, quantum discord has yet to become a standard tool in experimental studies of correlations. We propose an optical circuit for attaining quantum measurement advantage in a system that has no quantum entanglement. Our device</span></div>
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<div>produces symmetric two-qubit X -states with controllable anti-diagonal elements, and does not require entangled states as input. We discuss the use of this device in a two-qubit quantum game. When</div>
<div>entanglement is absent, the maximum quantum advantage in this game is 1/3 bit. A slightly diminished quantum advantage, 0.311 bit, can be</div>
<div>realized with a simplified transaction protocol.</div>
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</div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16252016-12-07T14:12:01-05:002016-12-07T14:12:01-05:00https://talks.cs.umd.edu/talks/1625Disorder-induced quantized pumping in a Floquet topological phaseParaj Titum - JQI, QuICS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, December 16, 2016, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><em><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Lunch served at 12:00</span></em></p>
<p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">In this talk, w</span><span style="color: #222222; font-size: 12.8px; font-family: 'helvetica neue', helvetica, roboto, arial, sans-serif;">e show that two-dimensional periodically driven quantum systems with spatial disorder admit a unique topological phase. This phase is characterized by a quasi-energy spectrum featuring chiral edge modes coexisting with a fully localized bulk. Such a spectrum is impossible for a time-independent, local Hamiltonian. These unique characteristics give rise to a new topologically protected non-equilibrium transport phenomenon: quantized, yet non-adiabatic, charge pumping. This phase is separated from a trivial Anderson insulating phase by a phase transition.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16272016-12-12T09:09:27-05:002016-12-12T09:09:27-05:00https://talks.cs.umd.edu/talks/1627Truly quantum Gibbs: Thermal state of a system whose charges don’t commuteNicole Yunger Halpern - Institute for Quantum Information and Matter, California Institute of Technology<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, June 7, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <div class="main-container container" style="box-sizing: border-box; margin-right: auto; margin-left: auto; padding-left: 15px; padding-right: 15px; width: 750px; overflow: auto;">
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<div style="box-sizing: border-box;">The grand canonical ensemble lies at the core of statistical mechanics. A small system <span style="box-sizing: border-box;">thermalizes to this state while exchanging heat and particles with a bath. A quantum system may </span><span style="box-sizing: border-box;">exchange quantities, or “charges,” represented by operators that fail to commute. Whether such a </span><span style="box-sizing: border-box;">system thermalizes, and what form the thermal state has, concerns truly quantum </span><span style="box-sizing: border-box;">thermodynamics.</span></div>
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<div style="box-sizing: border-box;">I characterize this state in three ways: First, I generalize the system-and-bath microcanonical <span style="box-sizing: border-box;">ensemble. Tracing out the bath yields the system’s thermal state. Second, this thermal state is </span><span style="box-sizing: border-box;">expected to be the fixed point of typical dynamics. Finally, the thermal state is completely </span><span style="box-sizing: border-box;">passive (unable to output thermodynamic work) in a resource-theory model for thermodynamics. </span><span style="box-sizing: border-box;">This study opens new avenues into equilibrium in the presence of quantum noncommutation.</span></div>
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<div style="box-sizing: border-box;"><u style="box-sizing: border-box;">References:</u></div>
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<div style="box-sizing: border-box;">Yunger Halpern et al. Nature Communications 7, 12051 (2016).</div>
<div style="box-sizing: border-box;"><span style="box-sizing: border-box;">This work was conducted with Philippe Faist, Jonathan Oppenheim, and Andreas Winter.</span></div>
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</footer><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16342016-12-20T08:45:36-05:002016-12-20T09:35:42-05:00https://talks.cs.umd.edu/talks/1634Scattering and quantum informationDan Carney - University of British Columbia<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, December 21, 2016, 10:00-11:00 am<br><br><b>Abstract:</b> <p><span style="color: #500050; font-family: arial, sans-serif; font-size: 12.8px;">In high energy and gravitational physics, the S-matrix is the starting point for studying any fundamental physics in asymptotically flat spacetimes. In the context of information theory, the S-matrix can be viewed simply as one of many possible unitary time evolution operators. I'll give some simple examples highlighting the overlap of these views; in particular, I will discuss the interplay of entanglement with relativistic scattering.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16402017-01-04T08:58:17-05:002017-01-04T08:58:17-05:00https://talks.cs.umd.edu/talks/1640Drainage solutions for quantum systemsVictor Albert - Yale University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, January 5, 2017, 1:00-2:00 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Lindbladians, one of the simplest extensions of Hamiltonian-based quantum mechanics, are used to describe “drainage” (i.e., decay) and decoherence of a quantum system induced by the system's environment. While traditionally viewed as detrimental to fragile quantum properties, a tunable environment offers the ability to drive the system toward exotic phases of matter, which may be difficult to stabilize in nature, or toward protected subspaces, which can be used to store and process quantum information. An important property of Lindbladians is their behavior in the limit of infinite time, and in this talk I will discuss a formula for the map corresponding to infinite-time Lindbladian evolution. This formula allows us to determine to what extent decay affects a system's linear or adiabatic response. It also allows us to determine geometrical structures (holonomy, curvature, and metric) associated with adiabatically deformed steady-state subspaces.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16412017-01-06T08:37:38-05:002017-03-17T09:01:55-04:00https://talks.cs.umd.edu/talks/1641Tunneling in Quantum Adiabatic OptimizationWim van Dam - Department of Computer Science, Department of Physics, UC Santa Barbara<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, March 29, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">This talk will address several aspects of tunneling when attempting quantum adiabatic optimization (QAO). First, I derive how the width and height of potential barriers affect the minimal spectral gap of the QAO algorithm. This derivation uses elementary techniques and confirms and extends an unpublished folklore result by Goldstone. Next, </span></p>
<div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">I discuss to which extend the asymptotic scaling of spectral gaps is relevant for reasonably sized systems. For tunneling we will see that the asymptotic behavior of the spectral gap does not accurately describe the exact gap behavior for systems of less than 10^12 qubits. Lastly, we ask what happens if we run the QAO algorithm faster than the adiabatic condition prescribes, i.e. if we perform non-adiabatic (or diabetic) optimization. I will show that typically the runtime suggested by the adiabatic theorem is not only a sufficient, but also necessary. This result indicates that for generic problem instances non-adiabatic optimization will not outperform QAO, although there are atypical exceptions to this rule. </div>
<div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><br>This is joint work with Lucas Brady.</div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16422017-01-09T09:07:50-05:002017-01-09T09:08:00-05:00https://talks.cs.umd.edu/talks/1642Simulating large quantum circuits on a small quantum computerMaris Ozols - University of Cambridge<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, January 18, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="MsoNoSpacing"><span style="font-size: 12.0pt; ">This talk will explore strategies for simulating large quantum circuits on a classical computer that has access to a small quantum device. We show that a quantum circuit, represented by a tensor network, can be cut into smaller pieces and each piece executed independently on a smaller device by simulating contraction of the corresponding smaller tensor network. Assuming a partition with not too many edges between different parts can be found, we provide efficient algorithms for simulating such circuits. While in general the simulation cost scales exponentially in the total number of edges between different parts, the size of the quantum memory required scales only linearly in the degree of each part.</span></p>
<p class="MsoNoSpacing"><span style="font-size: 12.0pt; "> </span></p>
<p class="MsoNoSpacing"><span style="font-size: 12.0pt; ">This talk is based on joint work with:</span></p>
<p class="MsoNoSpacing"><span style="font-size: 12.0pt; "> </span></p>
<p class="MsoNoSpacing"><span style="font-size: 12.0pt; ">Aram Harrow (MIT)</span></p>
<p class="MsoNoSpacing"><span style="font-size: 12.0pt; ">Tianyi Peng (Tsinghua University)</span></p>
<p class="MsoNoSpacing"><span style="font-size: 12.0pt; ">Xiaodi Wu (University of Oregon)</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16432017-01-10T09:45:25-05:002017-01-10T09:45:25-05:00https://talks.cs.umd.edu/talks/1643Complexity of quantum impurity modelsSergey Bravyi - IBM Research<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, February 8, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p style="background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;"><span style="font-size: 9.5pt; font-family: 'Arial','sans-serif'; color: #222222;">I will discuss classical algorithms for computing low-energy states of quantum impurity models. Such models describe a bath of free fermions coupled to a small interacting subsystem called an impurity. Hamiltonians of this form were famously studied by Anderson, Kondo, Wilson and others in 1960s. Impurity models also play the central role in modern material simulation algorithms based on the DMFT method. Quite recently it was suggested that DMFT simulation algorithms may benefit from quantum computers. As a first step, one may wish to use a quantum computer for preparing the ground state of an impurity model and extracting some information about its dynamics such as the impurity Green's function. This motivates the question of whether ground states of impurity models posses any simple structure and under what conditions they can be prepared efficiently. Here we show that ground states of impurity models can be approximated by low-rank Gaussian states -- superpositions of a small number of fermionic Gaussian states. As a corollary we obtain a classical algorithm for approximating the ground energy of impurity models. The running time of our algorithm is polynomial in the system size and quasi-polynomial in the inverse approximation error.<span class="apple-converted-space"> </span><br> <br> Based on a joint work with David Gosset</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16722017-01-30T10:23:49-05:002017-01-30T10:23:49-05:00https://talks.cs.umd.edu/talks/1672Multipartite entanglement detection with one random observableMinh Tran - QuICS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, February 3, 2017, 12:15-1:15 pm<br><br><b>Abstract:</b> <div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"><em style="box-sizing: border-box;">Lunch served at 12:00</em></div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"> </div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">We show that repeatedly measuring a many-body state in random local bases can detect entanglement. For pure states it is also asymptotically sufficient. In particular, if a state is sufficiently entangled, measuring only one randomly chosen observable can reveal multipartite entanglement with high probability. We demonstrate this feature with multipartite GHZ states and show that probability of success increases with number of subsystems. Finally, we discuss generalization from 2-level system to arbitrary dimension. </div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"> </div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Phys. Rev. A 92, 050301(R)(2015) </div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Phys. Rev. A 94, 042302 (2016)</div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16732017-01-30T10:26:43-05:002017-02-06T09:19:31-05:00https://talks.cs.umd.edu/talks/1673Geometric inequalities for bosonic quantum systemsRobert Koenig - TU Munich<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Monday, February 13, 2017, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Shannon's entropy power inequality gives a lower bound on the entropy power of the sum of two independent random variables in terms of the individual entropy powers. This statement and some of its consequences are information-theoretic counterparts of certain geometric inequalities. In this talk, I will give an overview of analogous statements for bosonic quantum systems. The first concerns a certain convolution operation between two quantum states: here two independent bosonic modes combine at a beamsplitter. The second involves an operation (originally introduced by Werner) combining a probability distribution on phase space with a quantum state of a bosonic mode. The inequalities have application to certain semigroups as well as capacity problems.</span><br style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><br style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">The talk is based on joint work with Stefan Huber, Graeme Smith, and Anna Vershynina. </span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16762017-02-01T10:08:01-05:002017-02-01T10:08:01-05:00https://talks.cs.umd.edu/talks/1676Cavity Cooling of Many AtomsKristin Beck - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, February 10, 2017, 12:15-1:15 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"><em style="box-sizing: border-box;">Lunch served at 12:00</em></p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"><span style="box-sizing: border-box;">We demonstrate cooling of an atomic ensemble from</span><span class="m_5310090783153959029gmail-m_-8131231778813979081inbox-inbox-Apple-converted-space" style="box-sizing: border-box;"> </span><span style="box-sizing: border-box;">200 µK to 10 µK in 100ms using an optical cavity and light that is far detuned from the atomic transitions. The cavity modifies the atomic emission spectrum which allows us to extract thermal kinetic energy from the atomic system. I'll describe the experiment and our cooling method, place it in the context of other common atomic cooling methods, and provide outlook for applying this technique to cool more atoms with more complicated energy level diagrams. (Preprint : arXiv:1701.01226)</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16882017-02-08T14:31:57-05:002017-02-08T14:31:57-05:00https://talks.cs.umd.edu/talks/1688Optomechanically-induced chiral transport of phonons in one dimensionXunnong Xu - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, February 17, 2017, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><em><span style="font-family: arial, helvetica, sans-serif; font-size: 12.8px;">Lunch served at 12:00</span></em></p>
<p><span style="font-family: arial, helvetica, sans-serif; font-size: 12.8px;">Non-reciprocal devices, with one-way transport properties, form a key component for isolating and controlling light in photonic systems. Optomechanical systems have emerged as a potential platform for optical non-reciprocity, due to ability of a pump laser to break time and parity symmetry in the system. Here we consider how the non-reciprocal behavior of light can also impact the transport of sound in optomechanical devices. We focus on the case of a quasi one dimensional optical ring resonator with many mechanical modes coupled to light via the acousto-optic effect. The addition of disorder leads to finite diffusion for phonon transport in the material, largely due to elastic backscattering between clockwise and counter-clockwise phonons. We show that a laser pump field, along with the assumption of high quality-factor, sideband-resolved optical resonances, suppresses the effects of disorder and leads to the emergence of chiral diffusion, with direction-dependent diffusion emerging in a bandwidth similar to the phase-matching bandwidth for Brillouin scattering. A simple diagrammatic theory connects the observation of reduced mechanical linewidths directly to the associated phonon diffusion properties, and helps explain recent experimental results.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/16932017-02-13T09:48:53-05:002017-02-13T09:48:53-05:00https://talks.cs.umd.edu/talks/1693Quantum Entanglement, Sum-of-Squares and the Log-Rank ConjecturePravesh Kothari - Princeton University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, February 22, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <div class="m_4608073653795385139gmail_msg" style="color: #212121; font-family: arial, sans-serif; font-size: 12.8px;">This talk will be about a sub-exponential time algorithm for the Best Separable State (BSS) problem. <br class="m_4608073653795385139gmail_msg">
<div class="m_4608073653795385139gmail_msg">
<div class="m_4608073653795385139gmail_msg">For every constant \eps>0, we give an<span class="m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-Apple-converted-space m_4608073653795385139gmail_msg"> </span><span id="m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-135" class="m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr_ m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr_135 m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr-alert m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr_spell m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr_run_anim m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-ContextualSpelling m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-ins-del m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-multiReplace m_4608073653795385139gmail_msg" style="display: inline; border-bottom: 2px solid transparent; background-repeat: no-repeat; color: inherit; font-size: inherit;">exp</span>(\sqrt(n) \poly log(n))-time algorithm for the 1 vs 1-\eps BSS problem of distinguishing, given an n^2 x n^2 matrix M corresponding to a quantum measurement, between the case that there is a separable (i.e., non-entangled) state \rho that M accepts with probability 1, and the case that every separable state is accepted with probability at most 1-\eps.</div>
<div class="m_4608073653795385139gmail_msg"> </div>
<div class="m_4608073653795385139gmail_msg">Equivalently, our algorithm takes the description of a subspace W \subset F^{n^2} (where F can be either the real or complex field) and distinguishes between the case that W contains a rank one matrix, and the case that every rank one matrix is at least \eps far (in<span class="m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-Apple-converted-space m_4608073653795385139gmail_msg"> </span><span id="m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-1353" class="m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr_ m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr_1353 m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr-alert m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr_gramm m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr_run_anim m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-Grammar m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-only-ins m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-doubleReplace m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-replaceWithoutSep m_4608073653795385139gmail_msg" style="display: inline; border-bottom: 2px solid transparent; background-repeat: no-repeat; color: inherit; font-size: inherit;">Euclidean</span> distance) from W. </div>
<div class="m_4608073653795385139gmail_msg"> </div>
<div class="m_4608073653795385139gmail_msg">The algorithm is based on the sum-of-squares semidefinite programming hierarchy - a powerful hierarchy of semidefinite programming relaxations that has recently been used to design fast approximation algorithms for problems in combinatorial optimization, machine learning and quantum information. </div>
<div class="m_4608073653795385139gmail_msg"> </div>
<div class="m_4608073653795385139gmail_msg">In this talk, I'll use the BSS problem as an example to illustrate a general rounding paradigm for the sum-of-squares algorithm. Somewhat surprisingly, a key technical step in the instantiation of this paradigm to analyze a rounding scheme for the BSS problem will be inspired by the recent breakthrough on the log-rank conjecture of Lovett (STOC'14, JACM'16) who showed that the communication complexity of every rank-n Boolean matrix is bounded by \sqrt{n}<span class="m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-Apple-converted-space m_4608073653795385139gmail_msg"> </span><span id="m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-498" class="m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr_ m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr_498 m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr-alert m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr_spell m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-gr_run_anim m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-ContextualSpelling m_4608073653795385139inbox-inbox-m_4325443789701608608inbox-inbox-ins-del m_4608073653795385139gmail_msg" style="display: inline; border-bottom: 2px solid transparent; background-repeat: no-repeat;">poly log</span>(n). </div>
</div>
</div>
<div class="m_4608073653795385139gmail_msg" style="color: #212121; font-family: arial, sans-serif; font-size: 12.8px;"> </div>
<div class="m_4608073653795385139gmail_msg" style="color: #212121; font-family: arial, sans-serif; font-size: 12.8px;">The talk will assume no specialized background. </div>
<div class="m_4608073653795385139gmail_msg" style="color: #212121; font-family: arial, sans-serif; font-size: 12.8px;"> </div>
<div class="m_4608073653795385139gmail_msg" style="color: #212121; font-family: arial, sans-serif; font-size: 12.8px;">Based on joint work with Boaz Barak (Harvard) and David Steurer (Cornell, IAS). </div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17052017-02-15T10:11:07-05:002017-02-15T10:11:07-05:00https://talks.cs.umd.edu/talks/1705Time-Reversal-Symmetry-Breaking Superconductivity in Epitaxial Bismuth/Nickel BilayersMehdi Kargarian - CMTC<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, February 24, 2017, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><em><span style="font-family: 'lucida grande', helvetica, arial, verdana, sans-serif; font-size: 14px;">Lunch served at 12:00</span></em></p>
<p>Superconductivity that spontaneously breaks time-reversal symmetry (TRS) has been found, so far, only in a handful of 3D crystals with bulk inversion symmetry. Here we report an observation of spontaneous TRS breaking in a 2D superconducting system without inversion symmetry: the epitaxial bilayer films of bismuth and nickel. The evidence comes from the onset of the polar Kerr effect at the superconducting transition in the absence of an external magnetic field, detected by the ultrasensitive loop-less fiber-optic Sagnac interferometer. Because of strong spin-orbit interaction and lack of inversion symmetry in a Bi/Ni bilayer, superconducting pairing cannot be classified as singlet or triplet. We propose a theoretical model where magnetic fluctuations in Ni induce superconducting pairing of the d_{xy} +- id_{x^2-y^2} orbital symmetry between the electrons in Bi. This order parameter spontaneously breaks the TRS and has a non-zero phase winding number around the Fermi surface, thus making Bi/Ni a rare example of a 2D topological superconductor.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17262017-03-03T09:08:50-05:002017-03-03T09:08:50-05:00https://talks.cs.umd.edu/talks/1726Josephson Junction Arrays in Circuit QED ArchitectureCosmic Raj - University of Tokyo, Nakamura group<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, March 8, 2017, 10:00-11:00 am<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Understanding and engineering of quantum many-body systems is a big challenge in quantum physics and quantum information processing. Studies in artificial quantum many-body systems with well-controlled parameters should play a central role for that purpose. One of the promising platforms for realizing an artificial quantum many-body system is a Josephson junction array (JJA). It consists of an array of superconducting islands connected by small Josephson junctions, where various kinds of classical and quantum Hamiltonians (such as Bose-Hubbard, XY Hamiltonians) can be implemented depending on parameters of the system. Here, we will present our recent progress of experimental study of JJAs using the circuit quantum electrodynamics (cQED) architecture. In contrast to the conventional transport measurements in JJAs, the cQED approach has some advantages: The system is weakly perturbed by the microwave excitation and properties of not only ground state but excited states are investigated at single photon level. In this talk, we particularly focus on our investigations of JJA in a magnetic field, and present some preliminary results of vortex lattice melting process.</span><br style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><br style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Cosmic will be visiting UMD Wed-Fri. Please contact Jake Taylor if you’d like to meet with him during his trip.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17122017-02-22T09:47:29-05:002017-02-22T09:47:29-05:00https://talks.cs.umd.edu/talks/1712Kinetic theory of dark solitons with tunable frictionHilary Hurst - JQI & CMTC<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, March 3, 2017, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">We study controllable friction in a system consisting of a dark soliton in a one-dimensional Bose gas and a non-interacting Fermi gas. The fermions act as impurity atoms, not part of the original condensate, that scatter off of the soliton. We investigate semiclassical dynamics of the dark soliton, a particle-like object with negative mass, and calculate its friction coefficient. Surprisingly, the amount of friction depends on the ratio of interspecies (impurity-condensate) to intraspecies (condensate-condensate) interaction strengths. By tuning this ratio, one can access a regime where the friction coefficient vanishes. Using this friction coefficient we develop a complete kinetic theory of the soliton, including the exact probability distribution function for the soliton. We find that both the trajectory and lifetime of the soliton are altered by friction, and in the presence of friction and an external confining potential the soliton can undergo Brownian motion. These results agree qualitatively with experimental observations by Aycock, et. al (PNAS 2017) in a similar system with bosonic impurity scatterers.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17132017-02-22T09:48:17-05:002017-02-27T10:26:46-05:00https://talks.cs.umd.edu/talks/1713Quantum homomorphic encryption for polynomial-sized circuitsChristian Schaffner - University of Amsterdam<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, March 8, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">We present a new scheme for quantum homomorphic encryption which is </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">compact and allows for efficient evaluation of arbitrary </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">polynomial-sized quantum circuits. Building on the framework of </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Broadbent and Jeffery [BJ15] and recent results in the area of </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">instantaneous non-local quantum computation [Spe15], we show how to </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">construct quantum gadgets that allow perfect correction of the errors </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">which occur during the homomorphic evaluation of T gates on encrypted </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">quantum data. Our scheme can be based on any classical (leveled) fully </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">homomorphic encryption (FHE) scheme and requires no computational </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">assumptions besides those already used by the classical scheme. The size </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">of our quantum gadget depends on the space complexity of the classical </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">decryption function – which aligns well with the current efforts to </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">minimize the complexity of the decryption function. </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Our scheme (or slight variants of it) offers a number of additional </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">advantages such as ideal compactness, the ability to supply gadgets “on </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">demand”, circuit privacy for the evaluator against passive adversaries, </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">and a three-round scheme for blind delegated quantum computation which </span><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">puts only very limited demands on the quantum abilities of the client.</span><br style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><br style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">joint work with Yfke Dulek and Florian Speelman</span><br style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><a style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #1155cc; text-decoration: none; font-family: arial, sans-serif; font-size: 12.8px;" href="https://arxiv.org/abs/1603.09717" rel="noreferrer">https://arxiv.org/abs/1603.<wbr></wbr>09717</a><br style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><span style="margin: 0px; padding: 0px; border: 0px; vertical-align: baseline; color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">appeared at CRYPTO 2016 and QIP 2017</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17142017-02-22T09:49:38-05:002017-03-10T08:39:28-05:00https://talks.cs.umd.edu/talks/1714Quantum-Proofs.zipZhengfeng Ji - UT Sydney<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, March 15, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">In this talk, I will unzip a recent progress on quantum <span style="box-sizing: border-box;">interactive proofs---communications in quantum multi-prover </span>interactive proofs can be exponentially compressed. By combining <span style="box-sizing: border-box;">several old good ideas in quantum proofs, we will show how to </span><span style="box-sizing: border-box;">construct a protocol that transforms any quantum multi-prover </span><span style="box-sizing: border-box;">interactive proof system into a nonlocal game, a scaled-down version </span><span style="box-sizing: border-box;">the proof system in which questions consist of a logarithmic number of </span><span style="box-sizing: border-box;">bits and answers of a constant number of bits. As a corollary, this </span><span style="box-sizing: border-box;">proves that nonlocal games are complete for QMIP*, and therefore </span><span style="box-sizing: border-box;">NEXP-hard. This establishes that nonlocal games are provably harder </span><span style="box-sizing: border-box;">than classical games. Our result reveals an important difference </span><span style="box-sizing: border-box;">between classical and quantum multi-prover proofs, and makes </span><span style="box-sizing: border-box;">interesting implications for the multi-prover variant of the quantum </span><span style="box-sizing: border-box;">PCP conjecture.</span></div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17222017-03-01T11:05:14-05:002017-03-01T11:05:14-05:00https://talks.cs.umd.edu/talks/1722Some recent progress on quantum information complexityPenghui Yao - QuICS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, March 10, 2017, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-size: 12.8px; font-family: arial, helvetica, sans-serif;">Information complexity (IC) was introduced </span><span style="color: #222222; font-size: 12.8px; font-family: arial, helvetica, sans-serif;">around 2000</span><span style="color: #222222; font-size: 12.8px; font-family: arial, helvetica, sans-serif;"> to study communication complexity (CC) and it turns out to be one of the most powerful methods. Many elegant message-compression algorithms have been discovered to compress protocols with low IC since then. After q</span><span style="font-size: 12.8px; font-family: arial, helvetica, sans-serif; color: #333333;">uantum <span class="m_-5845013025691644111gmail-m_7036139039498733456gmail-il">information</span> <span class="m_-5845013025691644111gmail-m_7036139039498733456gmail-il">complexity</span><wbr></wbr> (QIC) was defined by Touchette in 2014, It is interesting to ask whether we are able to compress quantum protocols with low QIC via quantizing those classical message-compression algorithms. </span><span style="font-size: 12.8px; color: #333333; font-family: arial, helvetica, sans-serif;">In this talk, I will survey some recent results towards the direction in several different communication complexity settings. </span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17492017-03-30T13:45:02-04:002017-03-30T13:45:02-04:00https://talks.cs.umd.edu/talks/1749Detecting entanglement and non-local correlations of many-body quantum statesAntonio Acin - Institute for Photonic Sciences, Barcelona<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, April 5, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Quantum correlations are fundamental for quantum information protocols and for our understanding of many-body quantum physics. The detection of these correlations in these systems is challenging because it requires the estimation of an exponentially growing amount of parameters. We present methods to alleviate this problem and discuss their application to physically relevant quantum states.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17542017-04-06T08:49:15-04:002017-04-06T08:49:15-04:00https://talks.cs.umd.edu/talks/1754Interactions on the surface of a three-dimensional topological insulatorRex Lundgren - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, April 7, 2017, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">The gapless surface states of three-dimensional topological insulators are a new form of matter, and there is much active research on exotic order on the surface of topological insulators due to electron-electron interactions. In this talk, we investigate electron-electron interactions on the surface of a three-dimensional topological insulator. First, we construct a phenomenological Landau theory for the two-dimensional helical Fermi liquid found on the surface of a three-dimensional time-reversal invariant topological insulator. By projecting quasiparticle states onto the Fermi surface, we obtain an effectively spinless, Landau theory with a single Landau parameter per angular momentum channel that captures the spin-momentum locking or nontrivial Berry phase of the Fermi surface. Next, we derive equilibrium properties, criteria for Fermi surface instabilities, and collective mode dispersions in terms of the projected Landau parameters. In particular, we investigate the nematic instability of the helical Fermi surface in detail and discuss various observable consequences of nematic order unique to helical Fermi liquids.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17552017-04-06T08:49:48-04:002017-04-07T14:03:46-04:00https://talks.cs.umd.edu/talks/1755Tests for small quantum devicesBen Reichardt - U. Southern California<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, April 12, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Reliable qubits are difficult to engineer. What can we do with just a few of them? Here are some ideas: </div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"> </div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">1. Memory/dimensionality test. An n-qubit system has 2^n dimensions---a big reason for quantum computers' exponential power! But systems with just polynomial(n) dimensions can look like they have n qubits. We give a test for verifying that your system really has 2^n dimensions. </div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"> </div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">2. Entanglement test. A Bell-inequality violation establishes that your systems share some entanglement (i.e., there's no classical explanation). We give a test to show that your systems share lots of entanglement. </div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"> </div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">3. Extended Einstein-Podolsky-Rosen (EPR) test. Classical hidden variables can't explain a Bell inequality violation, but another non-quantum theory could explain it: non-signaling correlations like the Popescu-Rohrlich nonlocal box. We give a test, using three spacelike-separated devices, to eliminate non-signaling explanations. </div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"> </div>
<div style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">4. Error correction test. Error correction will be needed for scalable quantum computers. But high qubit overhead makes it impractical for small devices. We show that a 7-qubit computer can fault tolerantly correct errors on one encoded qubit, and that a 17-qubit computer can protect and compute fault tolerantly on seven encoded qubits. </div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17562017-04-06T08:50:25-04:002017-04-06T08:50:25-04:00https://talks.cs.umd.edu/talks/1756Thermal radiation from a strongly correlated one-dimensional electron liquidWade DeGottardi - JQI & IREAP<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, April 14, 2017, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">In this talk, I will present recent work on the properties of radiation from a </span><span style="box-sizing: border-box; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">one-dimensional electron liquid. Because of the large mismatch between the speed of light and the Fermi velocity, radiation serves as a direct test of spectral weight of the system which is far `off-shell'. In the Luttinger liquid model, excitations of the electron liquid are described by non-interacting bosons and this spectral weight vanishes. Thus, radiation offers a direct test of behavior which is beyond the Luttinger liquid paradigm. I will discuss several examples of systems for which such radiation can be observed.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17572017-04-06T08:56:09-04:002017-04-10T08:47:57-04:00https://talks.cs.umd.edu/talks/1757Quantum Self-testingMatthew McKague - Queensland University of Technology<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, April 19, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="font-family: Calibri, Arial, Helvetica, sans-serif; color: #212121; font-size: 13.3333px;">Quantum self-testing is a tool that can allow us to test the honesty of </span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; color: #212121; font-size: 13.3333px;">quantum devices without needing to have access to any trusted quantum </span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; color: #212121; font-size: 13.3333px;">devices. Through classical information alone (measurement settings and </span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; color: #212121; font-size: 13.3333px;">outcomes, for example) we can verify that quantum devices are operating </span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; color: #212121; font-size: 13.3333px;">according to some specification, even if we have no information on how the </span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; color: #212121; font-size: 13.3333px;">devices are constructed. Self-testing can be used to test sources, </span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; color: #212121; font-size: 13.3333px;">measurements, and even entire quantum computations. In this talk I will go </span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; color: #212121; font-size: 13.3333px;">over the basics of self-testing and discuss some known self-tests and </span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; color: #212121; font-size: 13.3333px;">applications.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17582017-04-06T08:56:36-04:002017-04-19T13:38:27-04:00https://talks.cs.umd.edu/talks/1758Quantum information processing, machine learning and AI Vedran Dunjko - Univ. of Innsbruck<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, April 26, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="font-family: 'Segoe UI', Helvetica, Arial, sans-serif; font-size: medium;">The nascent field of Quantum Machine Learning has been generating a substantial buzz in the last few years. </span><span style="font-family: 'Segoe UI', Helvetica, Arial, sans-serif; font-size: medium;">The broad theme of this field is the interplay between the disciplines of quantum information processing (QIP) and of machine learning (ML). In this talk, I will review the basic trends in this new discipline. I will focus on the ever-growing evidence that not only do ML-type applications form one of the best reasons to build quantum computers </span><span style="font-family: 'Segoe UI', Helvetica, Arial, sans-serif; font-size: medium;">(barring perhaps quantum simulations and cryptography), but ML techniques </span><span style="font-family: 'Segoe UI', Helvetica, Arial, sans-serif; font-size: medium;">may significantly help bringing about large-scale quantum computers -- making ML and QIP a perfect match. </span><span style="font-family: 'Segoe UI', Helvetica, Arial, sans-serif; font-size: medium;">Following this, I will present a perspective on the field we have developed in Innsbruck, which broaches the broader topic of the interplay of artificial general intelligence (going beyond standard ML machinery) and quantum mechanics. </span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17672017-04-12T10:17:55-04:002017-04-12T10:17:55-04:00https://talks.cs.umd.edu/talks/1767Faster Pulse Sequences for Performing Arbitrary Rotations in Singlet-Triplet QubitsRobert Throckmorton - CMTC and JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, April 21, 2017, 12:15-1:15 pm<br><br><b>Abstract:</b> <div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><span class="m_-7246623484266089610gmail-m_-7593082764086402143gmail-largernormal">We present new composite pulse sequences for performing arbitrary rotations in singlet-triplet qubits that are faster than existing sequences. We consider two sequences for performing a z rotation, one that generalizes the Hadamard-x-Hadamard sequence, and another that generalizes a sequence by Guy Ramon </span><span class="m_-7246623484266089610gmail-m_-7593082764086402143gmail-largernormal">(G. Ramon, Phys. Rev. B 84, 155329 (2011)). We determine the time required to perform each sequence, and find that our "generalized Hadamard-x-Hadamard" sequence can always be made faster than the "generalized Ramon sequence". We then present similar sequences for performing x rotations, one that generalizes the Hadamard-z-Hadamard sequence and another that is based on Ramon's z rotation sequence. In this case, we find that the "Ramon-like" sequence is faster. We also present sequences for performing other rotations. We then find versions of these sequences dynamically corrected for noise-induced errors using SUPCODE (X. Wang et. al., PRA 89, 022310 (2014)).</span></div>
<div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><span class="m_-7246623484266089610gmail-m_-7593082764086402143gmail-largernormal"> </span></div>
<div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"><span class="m_-7246623484266089610gmail-m_-7593082764086402143gmail-largernormal">Reference: C. Zhang, RET, X-C. Yang, X. Wang, E. Barnes, and S. Das Sarma, arXiv:1701.03796 (submitted to PRL), plus currently unpublished work.</span></div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17742017-04-19T11:22:30-04:002017-04-19T11:22:30-04:00https://talks.cs.umd.edu/talks/1774Complexity of sampling as an order parameterAbhinav Deshpande - QuICS and JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, April 28, 2017, 12:15-1:15 pm<br><br><b>Abstract:</b> <div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">We consider the classical complexity of approximately simulating time evolution under spatially local quadratic bosonic Hamiltonians for time t. We obtain upper bounds on the scaling of t with the number of bosons, n, for which simulation is classically efficient. We also obtain a lower bound on the scaling of t with n for which this problem reduces to a general instance of the boson sampling problem and is hence hard, assuming the conjectures of Aaronson and Arkhipov [Proc. 43rd Annu. ACM Symp. Theory Comput. STOC '11]. We view these results in the light of classifying phases of physical systems based on parameters in the Hamiltonian and conjecture a link to dynamical phase transitions. In doing so, we combine ideas from mathematical physics and computational complexity to gain insight into the behavior of condensed matter systems.<br><br></div>
<p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Preprint: arXiv:1703.05332</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17802017-04-26T11:41:40-04:002017-05-01T09:59:30-04:00https://talks.cs.umd.edu/talks/1780Complete 3-Qubit Grover Search on a Programmable Quantum ComputerCaroline Figgatt - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, May 5, 2017, 12:15-1:15 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Searching large databases is an important problem with broad applications. The Grover search algorithm provides a powerful method for quantum computers to perform searches with a quadratic speedup in the number of required database queries over classical computers. Here, we report results for a complete three-qubit Grover search algorithm using the scalable quantum computing technology of trapped atomic ions, with better-than-classical performance. The algorithm is performed for all 8 possible single-result oracles and all 28 possible two-result oracles. Two methods of state marking are used for the oracles: a phase-flip method employed by other experimental demonstrations, and a Boolean method requiring an ancilla qubit that is directly equivalent to the state-marking scheme required to perform a classical search. All quantum solutions are shown to outperform their classical counterparts. We also report the first implementation of a Toffoli-4 gate, which is used along with Toffoli-3 gates to construct the algorithms; these gates have process fidelities of 70.5% and 89.6%, respectively.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17842017-05-02T09:40:09-04:002017-05-02T09:40:09-04:00https://talks.cs.umd.edu/talks/1784Quantum advantage with shallow circuitsDavid Gosset - IBM<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, June 28, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">We prove that constant-depth quantum circuits are more powerful than their classical counterparts. We describe an explicit (i.e., non-oracular) computational problem which can be solved with certainty by a constant-depth quantum circuit composed of one- and two-qubit gates. In contrast, we prove that any classical probabilistic circuit composed of bounded fan-in gates that solves the problem with high probability must have depth logarithmic in the input size. This is joint work with Sergey Bravyi and Robert Koenig (arXiv:1704.00690).</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/17982017-06-05T09:31:27-04:002017-06-05T09:31:27-04:00https://talks.cs.umd.edu/talks/1798Adaptive vs nonadaptive strategies in the quantum setting with applicationsFrédéric Dupuis - Masaryk University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, July 19, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"><span style="box-sizing: border-box;">We prove a general relation between adaptive and nonadaptive strategies in the quantum setting, i.e., between strategies where the adversary can or cannot adaptively base its action on some auxiliary quantum side information. Our relation holds in a very general setting, and is applicable as long as we can control the bit-size of the side information, or, more generally, its "information content". Since adaptivity is notoriously difficult to handle in the analysis of (quantum) cryptographic protocols, this gives us a very powerful tool: as long as we have enough control over the side information, it is sufficient to restrict ourselves to non-adaptive attacks.</span></p>
<p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"><span style="box-sizing: border-box;">We demonstrate the usefulness of this methodology with two examples. The first is a quantum bit commitment scheme based on 1-bit cut-and-choose. Since bit commitment implies oblivious transfer (in the quantum setting), and oblivious transfer is universal for two-party computation, this implies the universality of 1-bit cut-and-choose. The second example is a quantum bit commitment scheme proposed in 1993 by Brassard et al. It was originally suggested as an unconditionally secure scheme, back when this was thought to be possible. We partly restore the scheme by proving it secure in (a variant of) the bounded quantum storage model.</span></p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"><span style="box-sizing: border-box;">In both examples, the fact that the adversary holds quantum side information obstructs a direct analysis of the scheme, and we circumvent it by analyzing a non-adaptive version, which can be done by means of known techniques, and applying our main result.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18032017-06-13T09:16:02-04:002017-06-13T09:16:02-04:00https://talks.cs.umd.edu/talks/1803Fantastic errors and where to find themRobin Blume-Kohout - Sandia National Lab<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, June 29, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Quantum processors exist — several fully programmable devices with 5-16 qubits exist today, at least one of which (the IBM Quantum Experience) is publicly accessible. Running real circuits on real quantum processors is forcing us to recognize and tackle new, “exotic” errors. After reviewing some of the “standard” frameworks for quantum errors, I’ll discuss ongoing work in Sandia’s QCVV group on: (1) how to test and validate error models of any kind, and (2) how to conceptualize, model, test, and characterize novel error modes including: leakage, drift, crosstalk, context-dependence, and faulty measurements in the middle of circuits.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18172017-07-10T10:14:33-04:002017-07-10T10:14:33-04:00https://talks.cs.umd.edu/talks/1817Quantum dots and entanglementTobias Huber - JQI<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">2136 Computer and Space Sciences Building (CSS)</a><br>Friday, July 14, 2017, 4:00-5:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;"><span style="box-sizing: border-box;">In this talk I will introduce some basic principles of semiconductor quantum dots and show how their discrete energy spectrum can be used to generate entangled photon pairs and spin photon entanglement. I will show, how a virtual level and two photon excitation can be used to excite a (single photon) forbidden transition. And if the time allows, I will show how different degrees of freedom can be used simultaneously to generate hyper-entangled photon pairs.</span></p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">(<span style="box-sizing: border-box;">The <span class="m_9043561367136893760m_-5309842832168879153term-highlighted" style="box-sizing: border-box;">JQI</span> <span class="m_9043561367136893760m_-5309842832168879153term-highlighted" style="box-sizing: border-box;">summer</span> <span class="m_9043561367136893760m_-5309842832168879153term-highlighted" style="box-sizing: border-box;">school</span> is for students and postdocs, but others are welcome to join for refreshments afterwards; Discussion with refreshments at <span class="aBn" style="box-sizing: border-box;" tabindex="0"><span class="aQJ" style="box-sizing: border-box;">5:00pm</span></span></span><span style="box-sizing: border-box;">)</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18202017-07-13T09:03:01-04:002017-07-19T14:26:23-04:00https://talks.cs.umd.edu/talks/1820Periodically Driven Quantum SystemsParaj Titum - JQI & QuICS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, July 21, 2017, 4:00-5:00 pm<br><br><b>Abstract:</b> <div style="color: #212121; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 12.8px; word-spacing: 1px;"><span style="color: #222222; font-family: arial, sans-serif; word-spacing: 0px;">JQI Summer School</span></div>
<div style="color: #212121; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 12.8px; word-spacing: 1px;"> </div>
<div style="color: #212121; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 12.8px; word-spacing: 1px;"><span style="color: #222222; font-family: arial, sans-serif; word-spacing: 0px;">Periodically driven systems (also known as Floquet systems) have seen a lot of recent theoretical and experimental interest. In this talk, I will provide a survey of various examples of Floquet systems. I will start by explaining basic Floquet theory, and describe how to obtain the dynamics of such driven systems. Then I will show how periodic driving can be used to tune a trivial system into a desired topological phase of matter. Finally, I will discuss interacting Floquet phases and the problem of heating in these systems. If time permits, I will describe the recent realization of a new phase of matter - time crystals.</span></div>
<div style="color: #212121; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 12.8px; word-spacing: 1px;"><span style="font-family: Tahoma;"> </span></div>
<div style="color: #212121; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 12.8px; word-spacing: 1px;"><span style="font-family: Tahoma;">(</span><span style="background-color: #ffff00;">The <span class="m_2903034686785787867gmail-m_8437301497302636742m_-5309842832168879153term-highlighted" style="background-color: rgba(251, 246, 167, 0.498);">JQI</span> <span class="m_2903034686785787867gmail-m_8437301497302636742m_-5309842832168879153term-highlighted" style="background-color: rgba(251, 246, 167, 0.498);">summer</span> <span class="m_2903034686785787867gmail-m_8437301497302636742m_-5309842832168879153term-highlighted" style="background-color: rgba(251, 246, 167, 0.498);">school</span> is for students and postdocs, but others are welcome to join for refreshments and snacks afterward; Discussion with refreshments and snacks at <span class="aBn" style="border-bottom: 1px dashed #cccccc; position: relative; top: -2px; z-index: 0;" tabindex="0"><span class="aQJ" style="position: relative; top: 2px; z-index: -1;">5:00 pm</span></span></span><span style="font-size: 13px; font-family: Tahoma;">)</span></div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18222017-07-19T14:25:59-04:002017-07-19T14:25:59-04:00https://talks.cs.umd.edu/talks/1822Toward a full software stack for the quantum computing platformYunseong Nam - IonQ inc., QuICS, UMIACS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, July 28, 2017, 4:00-5:00 pm<br><br><b>Abstract:</b> <p>JQI Summer School</p>
<div style="color: #212121; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 12.8px; word-spacing: 1px;"><span style="color: #222222; font-family: arial, sans-serif; word-spacing: 0px;">With commercial quantum computers on the rise, the development of a full software stack that will support the quantum computing platform is becoming increasingly important. In this talk, I will provide an overview of several key ingredients of the stack, addressing simulation, circuit optimization, circuit placement, and native gate set. Some future works will be discussed towards the end of the talk. No prior knowledge of the subject is required</span></div>
<div style="color: #212121; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 12.8px; word-spacing: 1px;"><span style="font-family: Tahoma;"> </span></div>
<div style="color: #212121; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 12.8px; word-spacing: 1px;"><span style="font-family: Tahoma;">(</span><span style="background-color: #ffff00;">The <span class="m_5441127654401758497gmail-m_-1275819902747861976gmail-m_8437301497302636742m_-5309842832168879153term-highlighted" style="background-color: rgba(251, 246, 167, 0.498);"><span class="m_5441127654401758497gmail-il">JQI</span></span> <span class="m_5441127654401758497gmail-m_-1275819902747861976gmail-m_8437301497302636742m_-5309842832168879153term-highlighted" style="background-color: rgba(251, 246, 167, 0.498);"><span class="m_5441127654401758497gmail-il">summer</span></span> <span class="m_5441127654401758497gmail-m_-1275819902747861976gmail-m_8437301497302636742m_-5309842832168879153term-highlighted" style="background-color: rgba(251, 246, 167, 0.498);">school</span> is for students and postdocs, but others are welcome to join for refreshments and snacks afterward; Discussion with refreshments and snacks at <span class="aBn" style="border-bottom: 1px dashed #cccccc; position: relative; top: -2px; z-index: 0;" tabindex="0"><span class="aQJ" style="position: relative; top: 2px; z-index: -1;">5:00 pm</span></span></span><span style="font-size: 13px; font-family: Tahoma;">)</span></div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18232017-07-21T08:26:21-04:002017-07-21T08:39:11-04:00https://talks.cs.umd.edu/talks/1823 Full and efficient characterisation of non-Markovian quantum processesKavan Modi - Monash<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Friday, July 28, 2017, 1:00-2:00 pm<br><br><b>Abstract:</b> <p><span style="color: #212121; font-family: arial, sans-serif; font-size: 12.8px;">In science, we often want to characterise dynamical processes </span><span style="color: #212121; font-family: arial, sans-serif; font-size: 12.8px;">to identify the underlying physics and predict the future states of the system.</span><span style="color: #212121; font-family: arial, sans-serif; font-size: 12.8px;"> If the state of the system at any time depends only on the state of the system at the previous time-step and some predetermined rule then the dynamics are characterised with relative ease. </span><span style="color: #212121; font-family: arial, sans-serif; font-size: 12.8px;">For instance, the dynamics of quantum mechanical systems in isolation is described in this way. </span><span style="color: #212121; font-family: arial, sans-serif; font-size: 12.8px;">However, when a quantum system repeatedly interact with an environment, the environment often ’remembers’ information about the system's past. This leads to non-Markovian processes, which depend nontrivially on the state of the system at all times during its evolution. Such dynamics are not, in general, be easily characterised using conventional techniques. </span><span style="color: #212121; font-family: arial, sans-serif; font-size: 12.8px;">Indeed, since the early days of quantum mechanics it has been a challenge to describe non-Markovian processes. Here we will show, using operational tools from quantum information theory, how to fully characterise any non-Markovian process. Using this we give an unambiguous criteria for quantum Markov processes. </span><span style="color: #212121; font-family: arial, sans-serif; font-size: 12.8px;">Next, we construct a mapping from a multi-time process to a many-body state using linear (in the number of time steps) amount of bipartite entanglement. The many-body state can be measured to any desired precision, thus the process can be characterised to any desired precision.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18242017-07-24T09:51:34-04:002017-08-03T10:58:39-04:00https://talks.cs.umd.edu/talks/1824Pure state tomography with Pauli observablesJustin Yirka - Virginia Commonwealth University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, August 10, 2017, 1:00-1:30 pm<br><br><b>Abstract:</b> <p>This talk is a REU Final Presentation for QuICS.</p>
<p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Pure-state tomography requires expectation values on the order of the system’s dimension, a quadratic improvement compared to general tomography. We seek to understand the number of expectation values necessary to uniquely determine all pure states, with the additional restriction that we consider only the expectation values of Pauli observables. Applying results from classical computer science, we reduce this question to an instance of the hypergraph dualization problem, yielding a conjectured upper bound on the necessary number of expectation values. Our conjecture is conditioned on further understanding the possible linear combinations of Pauli observables.</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">This is ongoing, joint work with Jianxin Chen and Amir Kalev. Part of this work was supported by an NSF REU while an undergraduate intern at QuICS.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18252017-07-24T09:52:33-04:002017-08-03T10:58:56-04:00https://talks.cs.umd.edu/talks/1825On the Relationship between Lower Bound Methods in Communication ComplexityJiahui Liu & Prayaag Venkat - Columbia University & UMD<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, August 10, 2017, 1:30-2:00 pm<br><br><b>Abstract:</b> <p>This talk is a REU Final Presentation for QuICS.</p>
<p><span style="color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Communication complexity studies the minimum number of bits distributed parties must communicate in order to perform some joint computation. In the restricted model of communication complexity, unconditional lower bounds can be proven, leading to hardness results for many other problems of interest in computer science. Over the past few decades, numerous lower bound methods have been introduced. Present work aims to unify these lower bounds through linear programming and characterize the relationship between them. In this talk, we discuss ongoing work that aims to investigate the relationship between the three most powerful of these methods, the partition bound, the relaxed partition bound, and the relative discrepancy bound. This talk is based on work done this summer by Jiahui Liu and Prayaag Venkat, under the guidance of Penghui Yao and Andrew Childs.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18272017-07-24T15:50:27-04:002017-07-24T15:50:27-04:00https://talks.cs.umd.edu/talks/1827Conditional Mutual Information and Quantum SteeringEneet Kaur - Louisiana State University<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, August 3, 2017, 2:00-3:00 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Quantum </span><span class="m_-6149512615895881601gmail-il" style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">steering</span><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"> has recently been formalized in the framework of a resource theory of </span><span class="m_-6149512615895881601gmail-il" style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">steering</span><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">, and several quantifiers have already been introduced. We propose the intrinsic steerability as an information-theoretic quantifier of </span><span class="m_-6149512615895881601gmail-il" style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">steering</span><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"> that uses conditional mutual information to measure the deviation of a given assemblage from an assemblage having a local hidden-state model. We prove that this quantifier is a </span><span class="m_-6149512615895881601gmail-il" style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">steering</span><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"> monotone (i.e., it is faithful, convex, and non-increasing under one-way local operations and classical communication). This suggests that the intrinsic steerability should find applications in protocols where </span><span class="m_-6149512615895881601gmail-il" style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">steering</span><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"> is relevant. We then consider a restricted version of intrinsic steerability, which is a </span><span class="m_-6149512615895881601gmail-il" style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">steering</span><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;"> monotone under a restricted set of free operations. The restricted intrinsic steerability is additive with respect to tensor-product assemblages, and it is also monogamous.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18362017-07-27T13:54:02-04:002017-07-27T13:54:02-04:00https://talks.cs.umd.edu/talks/1836Measurement aspects of statistical mechanics, classical and quantum alike.Jiehang Zhang - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, August 4, 2017, 4:00-5:00 pm<br><br><b>Abstract:</b> <p>*This is the JQI Summer School*</p>
<div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">
<p class="MsoNormal" style="margin: 0px; font-size: 12.8px;">Is information a physical quantity? Or perhaps it is merely a result of our logical deduction. These two don’t conflict with each other in a Bayesian framework, as two probabilities always exist: one from the statistical sample to be measurement, and one from the conclusion we draw from these measurements. I will discuss the information and measurement aspects of statistical mechanics: what happens after the moment that we stick a thermometer into a box. This sounds classical, but the quantum case is not much different. Discussions are based on the pioneering work by E. T. Jaynes [1], and recent realizations and extensions to the same principle [2]. No prior knowledge is required. </p>
<p class="MsoNormal" style="margin: 0px; font-size: 12.8px;"> </p>
<p class="MsoNormal" style="margin: 0px; font-size: 12.8px;">[1] E. T. Jaynes, Phys. Rev. <strong>106</strong>, 620 (1957).</p>
[2] M. N. Bera, A. Riera, M. Lewenstein, A. Winter. Arxiv 1707.01750 (2017).</div>
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<div style="color: #212121; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 12.8px; word-spacing: 1px;"><span style="font-family: Tahoma;">(</span><span style="background-color: #ffff00;">The <span class="m_557076531211114239gmail-m_-5616859605525734011gmail-m_-1275819902747861976gmail-m_8437301497302636742m_-5309842832168879153term-highlighted" style="background-color: rgba(251, 246, 167, 0.498);"><span class="m_557076531211114239gmail-m_-5616859605525734011gmail-il">JQI</span></span> <span class="m_557076531211114239gmail-m_-5616859605525734011gmail-m_-1275819902747861976gmail-m_8437301497302636742m_-5309842832168879153term-highlighted" style="background-color: rgba(251, 246, 167, 0.498);"><span class="m_557076531211114239gmail-m_-5616859605525734011gmail-il">summer</span></span> <span class="m_557076531211114239gmail-m_-5616859605525734011gmail-m_-1275819902747861976gmail-m_8437301497302636742m_-5309842832168879153term-highlighted" style="background-color: rgba(251, 246, 167, 0.498);">school</span> is for students and postdocs, but others are welcome to join for refreshments and snacks afterward; Discussion with refreshments and snacks at <span class="aBn" style="border-bottom: 1px dashed #cccccc; position: relative; top: -2px; z-index: 0;" tabindex="0"><span class="aQJ" style="position: relative; top: 2px; z-index: -1;">5:00 pm</span></span></span><span style="font-size: 13px; font-family: Tahoma;">)</span></div>
</div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18382017-08-01T09:29:54-04:002017-08-01T15:09:04-04:00https://talks.cs.umd.edu/talks/1838Spectral correlations among interfering nonidentical photons in universal linear opticsVincenzo Tamma - University of Portsmouth<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Thursday, September 7, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p class="m_4043459213777657938gmail-m_-6681455775705337225gmail-p1" style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Multiphoton quantum interference underpins fundamental tests of quantum mechanics and quantum technologies. Consequently, the detrimental effect of photon distinguishability in multiphoton interference experiments can be catastrophic. In this talk, we describe how accessing the spectral properties of an arbitrary number of photons initially distinguishable in their quantum states allows the scalable restoration of quantum interference in arbitrary linear optical networks, without the need for additional filtering or post selection. Even more interestingly, we show how harnessing the full spectra of multiphoton quantum information by frequency and time resolved correlation measurements enables the characterization of multiphoton networks and states, produces a wide variety of multipartite entanglement, and increases the possibilities to achieve quantum computational supremacy. Furthermore, the multiphoton interference techniques described here pave the way to a scaling-up of multiphoton interference experiments. These results are therefore of profound interest for future applications of universal spectrally resolved linear optics across fundamental science and quantum technologies with photons with experimentally different spectral properties.</p>
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<div style="font-size: 12.8px;">References</div>
<div style="font-size: 12.8px;"><span style="font-size: 12.8px;">[1] S. Laibacher and V. Ta</span><span style="font-size: small;">mma, arXiv:1706.05578</span></div>
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<div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">[2] V. Tamma and S. Laibacher, Phys. Rev. Lett. 114, 243601 (2015)</div>
<div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">[3] S. Laibacher and V. Tamma, Phys. Rev. Lett. 115, 243605 (2015)</div>
<p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">[4] V. Tamma and S. Laibacher, Quantum Inf. Process. 15(3), 1241-1262 (2015) </span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18402017-08-03T11:27:04-04:002017-08-03T11:27:04-04:00https://talks.cs.umd.edu/talks/1840Entanglement in many-body quantum systemsJim Garrison - JQI/QuICS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, August 11, 2017, 4:00-5:00 pm<br><br><b>Abstract:</b> <div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">
<div style="color: #212121; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; word-spacing: 1px;"><span style="font-family: arial, sans-serif; color: #222222;">*JQI Summer School*</span></div>
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<div style="color: #212121; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; word-spacing: 1px;"><span style="font-family: arial, sans-serif; color: #222222;">A system's entanglement structure can provide deep insights into a quantum phase of matter. After introducing the von Neumann entanglement entropy, I will discuss area laws and their violations in the ground states of quantum many-body systems, focusing on rigorously-proven results as well as simple examples which can guide intuition. I also plan to introduce a generalization of the von Neumann entropy known as the Renyi entropy, after which I will discuss its special applications in analytics, numerics, and experimental protocols for measuring entanglement. Time permitting, I will give a brief introduction to matrix product state methods and discuss their role in simulating 1D systems with low entanglement.</span></div>
<div class="m_-1383770551451951679m_-5522315282636986262gmail-yj6qo m_-1383770551451951679m_-5522315282636986262gmail-ajU" style="margin: 2px 0px 0px;"> </div>
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<div style="color: #212121; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; word-spacing: 1px;"><span style="font-family: Tahoma;">(</span><span style="background-color: #ffff00;">The <span class="m_-1383770551451951679m_-5522315282636986262gmail-m_-3261270656132798447gmail-m_-5616859605525734011gmail-m_-1275819902747861976gmail-m_8437301497302636742m_-5309842832168879153term-highlighted" style="background-color: rgba(251, 246, 167, 0.498);"><span class="m_-1383770551451951679m_-5522315282636986262gmail-m_-3261270656132798447gmail-m_-5616859605525734011gmail-il">JQI</span></span> <span class="m_-1383770551451951679m_-5522315282636986262gmail-m_-3261270656132798447gmail-m_-5616859605525734011gmail-m_-1275819902747861976gmail-m_8437301497302636742m_-5309842832168879153term-highlighted" style="background-color: rgba(251, 246, 167, 0.498);"><span class="m_-1383770551451951679m_-5522315282636986262gmail-m_-3261270656132798447gmail-m_-5616859605525734011gmail-il">summer</span></span> <span class="m_-1383770551451951679m_-5522315282636986262gmail-m_-3261270656132798447gmail-m_-5616859605525734011gmail-m_-1275819902747861976gmail-m_8437301497302636742m_-5309842832168879153term-highlighted" style="background-color: rgba(251, 246, 167, 0.498);">school</span> is for students and postdocs, but others are welcome to join for refreshments and snacks afterward; Discussion with refreshments and snacks at <span class="aBn" style="border-bottom: 1px dashed #cccccc; position: relative; top: -2px; z-index: 0;" tabindex="0"><span class="aQJ" style="position: relative; top: 2px; z-index: -1;">5:00 pm</span></span></span><span style="font-size: 13px; font-family: Tahoma;">)</span></div>
</div><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18422017-08-11T12:02:30-04:002017-08-11T12:02:30-04:00https://talks.cs.umd.edu/talks/1842Keldysh-ETH quantum computation algorithmJim Freericks - Georgetown University<br><a href="https://cmns.umd.edu/psc">3150 Physical Sciences Complex (PSC)</a><br>Wednesday, October 11, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">We develop an efficient and fast quantum computational scheme to determine the equilibrium Green's functions at finite temperature without requiring any adiabatic state preparation steps. The approach works for generic models that obey the eigenstate thermalization hypothesis and one can show the short-time behavior of the Green's functions is produced exactly by this method. We also describe cooling schemes that could be invoked to reach lower temperatures than what can be reached by simple interaction-strength ramping. The approach requires one qbit per orbital degree of freedom plus one additional global ancilla qbit. Cooling requires additional ancilla qbits, with more qbits providing additional cooling power. We end with a discussion on how this algorithm can be implemented now on currently available quantum computers like the IBM 5 qbit machine.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18442017-08-24T14:23:44-04:002017-08-24T14:23:44-04:00https://talks.cs.umd.edu/talks/1844Multi-Species Trapped-Ion Node for Quantum NetworkingClay Crocker - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, September 1, 2017, 4:15-5:15 pm<br><br><b>Abstract:</b> <div style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Trapped atomic ions are a leading platform for quantum information networks, with long-lived identical qubit memories that can be locally entangled through their Coulomb interaction and remotely entangled through photonic channels. However, performing both local and remote operations in a single node of a quantum network requires extreme isolation between spectator qubit memories and qubits associated with the photonic interface. We achieve this isolation by cotrapping 171Yb+ and 138Ba+ qubits. We further demonstrate the ingredients of a scalable ion trap network node with two distinct experiments that consist of entangling the mixed species qubit pair through their collective motion and entangling a 138Ba+ qubit with an emitted visible photon.</div>
<p>*Snacks and drinks will be served at 4 pm*</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18482017-08-30T14:11:16-04:002017-08-30T15:09:36-04:00https://talks.cs.umd.edu/talks/1848Lyapunov Exponent and Out-of-Time-Ordered Correlator's Growth Rate in a Chaotic SystemEfim Rozenbaum - JQI and CMTC<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, September 8, 2017, 4:15-5:15 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">*Snacks and drinks will be served at 4 pm*</span></p>
<p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">It was proposed recently that the out-of-time-ordered four-point correlator (OTOC) may serve as a useful characteristic of quantum-chaotic behavior, because in the semi-classical limit, hbar -> 0, its rate of exponential growth resembles the classical Lyapunov exponent. Here, we calculate the four-point correlator, C(t), for the classical and quantum kicked rotor -- a textbook driven chaotic system -- and compare its growth rate at initial times with the standard definition of the classical Lyapunov exponent. Using both quantum and classical arguments, we show that the OTOC's growth rate and the Lyapunov exponent are in general distinct quantities, corresponding to the logarithm of phase-space averaged divergence rate of classical trajectories and to the phase-space average of the logarithm, respectively. The difference appears to be more pronounced in the regime of low kicking strength K, where no classical chaos exists globally. In this case, the Lyapunov exponent quickly decreases as K -> 0, while the OTOC's growth rate may decrease much slower showing higher sensitivity to small chaotic islands in the phase space. We also show that the quantum correlator as a function of time exhibits a clear singularity at the Ehrenfest time t_E: transitioning from a time-independent value of t^-1 ln[C(t)] at t < t_E to its monotonous decrease with time at t>t_E. We note that the underlying physics here is the same as in the theory of weak (dynamical) localization [Aleiner and Larkin, Phys. Rev. B 54, 14423 (1996); Tian, Kamenev, and Larkin, Phys. Rev. Lett. 93, 124101 (2004)] and is due to a delay in the onset of quantum interference effects, which occur sharply at a time of the order of the Ehrenfest time.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18562017-09-07T09:45:09-04:002017-09-07T09:45:09-04:00https://talks.cs.umd.edu/talks/1856Entanglement spectroscopy on a quantum computerSonika Johri - Intel Labs, Intel Corporation, Hillsboro, OR<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, September 15, 2017, 4:15-5:15 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">One important application of quantum computers is efficiently simulating many-body quantum systems. The quantum computing equivalent of the vast array of diagnostic tools that extract information from classical numerical simulation are still being developed. Along these lines, we present a quantum algorithm to compute the entanglement spectrum of arbitrary quantum states. The interesting universal part of the entanglement spectrum is typically contained in the largest eigenvalues of the density matrix which can be obtained from the lower Renyi entropies through the Newton-Girard method. Obtaining the ‘p’ largest eigenvalues (lambda_1 > lambda_2… > lambda_p) requires a parallel circuit depth of O(p(lambda_1/lambda_p)^p) and O(p log(N)) qubits where up to ‘p’ copies of the quantum state defined on a Hilbert space of size ‘N’ are needed as the input. We validate this procedure for the entanglement spectrum of the topologically-ordered Laughlin wave function corresponding to the quantum Hall state at filling factor 1/3. Our scaling analysis exposes the tradeoffs between time and number of qubits for obtaining the entanglement spectrum in the thermodynamic limit using finite-size digital quantum computers. Importantly, we will also present results from implementing this algorithm on a digital quantum computing platform of trapped ion qubits to extract the second Renyi entropy of the ground state of a 2-site Fermi-Hubbard model.</span></p>
<p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">*Snacks and drinks will be served at 4 pm*</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18572017-09-11T09:35:23-04:002017-09-11T09:35:23-04:00https://talks.cs.umd.edu/talks/1857Entanglement transformation and the structure of matrix spaceYinan Li - UTS<br><a href="http://www.umd.edu/CampusMaps/bld_detail.cfm?bld_code=CSS">3100A Computer and Space Sciences Building (CSS)</a><br>Wednesday, October 11, 2017, 1:00-2:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Entanglement is arguably the most important physical resources in quantum information processing, and a fundamental task is to transform a multipartite entangled pure state into a bipartite entangled pure state shared between two specific parties. In this talk, we study the following scenario: given a pure tripartite state shared by Alice, Bob and Charlie, what kind of pure bipartite entangled state can be recovered with a nonzero probability by Alice and Bob with the help of Charlie under local operations and classical communication (a.k.a. SLOCC transformation)? Such a problem can be characterized by the maximal rank of a matrix space, i.e., the largest rank of matrices of a matrix space (linear space of matrices). We study this quantity and find a number of interesting properties, such as super-multiplicativity. By studying the behavior of maximal rank under tensor product, we obtain explicit formulas to compute the asymptotic entanglement transformation rate for a large family of tripartite states. Notably, utilizing certain results of the classification of matrix spaces, including the study of matrix semi-invariants in geometric invariant theory, we obtain a sufficient and necessary condition to decide whether a tripartite state can be transformed to the bipartite maximally entangled state by SLOCC, in the asymptotic setting. Interestingly, based on the recent seminal progress on the non-commutative rank problem, our characterization can be verified in deterministic polynomial time.</p>
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<p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Reference:</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Y Li, Y Qiao, X Wang and R Duan, “Tripartite-to-bipartite Entanglement Transformation by Stochastic Local Operations and Classical Communication and the Classification of Matrix Spaces,” arXiv:1612.06491, 2016</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18592017-09-13T09:49:58-04:002017-09-13T09:49:58-04:00https://talks.cs.umd.edu/talks/1859Out of equilibrium dynamical phase transition with trapped ion spinsJiehang Zhang - JQI<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, September 22, 2017, 4:15-5:15 pm<br><br><b>Abstract:</b> <p>*Snacks and drinks will be served at 4 pm*</p>
<p><span style="color: #222222; font-family: arial, sans-serif; font-size: 12.8px;">Trapped atomic ions are an ideal platform for building novel quantum systems from the ground up. The combination of long-lived qubit coherence time and mature laser manipulation techniques compose the building blocks of a quantum computer. We use this toolbox to engineer interacting many-body systems, where the spins are encoded in atomic hyperfine states and entangled via the shared motional quantum bus. This has enabled long-range quantum Ising models with individual measurement and control, which are scaled up to 50+ spins, where the dynamics is hard to tract classically. In this talk I will present our most recent observation of an out of equilibrium dynamical phase transition, where traditional statistical mechanics do not apply. The signatures of the phase transition is manifested in both low order observables such as magnetizations and two-body correlators, and becomes more distinct for higher order correlations such as the formation probability. We present the first experimental observation of this correlator with our single shot single-site resolved imaging capability.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18632017-09-15T11:03:13-04:002017-09-15T11:03:13-04:00https://talks.cs.umd.edu/talks/1863Quantum SDP-Solvers: Better upper and lower boundsAndrás Gilyén - CWI<br><a href="https://cmns.umd.edu/psc">3150 Physical Sciences Complex (PSC)</a><br>Wednesday, October 25, 2017, 11:00 am-12:00 pm<br><br><b>Abstract:</b> <p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Joint work with: Joran van Apeldoorn, Sander Gribling and Ronald de Wolf</p>
<p style="box-sizing: border-box; margin: 0px 0px 10px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">Brandao and Svore recently gave quantum algorithms for approximately solving semidefinite programs, which in some regimes are faster than the best-possible classical algorithms in terms of the dimension n of the problem and the number m of constraints, but worse in terms of various other parameters. In this paper we improve their algorithms in several ways, getting better dependence on those other parameters. To this end we develop new techniques for quantum algorithms, for instance a general way to efficiently implement smooth functions of sparse Hamiltonians, and a generalized minimum-finding procedure.</p>
<p style="box-sizing: border-box; margin: 0px; text-rendering: optimizeLegibility; color: #333333; font-family: Roboto, 'Helvetica Neue', Arial, sans-serif; font-size: 14px;">We also show limits on this approach to quantum SDP-solvers, for instance for combinatorial optimizations problems that have a lot of symmetry.<br style="box-sizing: border-box;">Finally, we prove some general lower bounds showing that in the worst case, the complexity of every quantum LP-solver (and hence also SDP-solver) has to scale linearly with mn when m\approx n, which is the same as classical.</p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>tag:talks.cs.umd.edu,2005:Talk/18712017-09-20T13:28:55-04:002017-09-20T13:28:55-04:00https://talks.cs.umd.edu/talks/1871Rigidity of the magic pentagram gameAmir Kalev - QuICS<br><a href="https://cmns.umd.edu/psc">2136 Physical Sciences Complex (PSC)</a><br>Friday, September 29, 2017, 4:15-5:15 pm<br><br><b>Abstract:</b> <p><span style="color: #222222; font-family: arial, sans-serif; font-size: 16px;">*Snacks and drinks will be served at 4 pm*</span></p>
<p><span style="color: #222222; font-family: arial, sans-serif; font-size: 16px;">A game is rigid if a near-optimal score guarantees, under the sole assumption of the validity of quantum mechanics, that the players are using an approximately unique quantum strategy. Rigidity has a vital role in quantum cryptography as it permits a strictly classical user to trust behavior in the quantum realm. This property can be traced back as far as 1998 (Mayers and Yao) and has been proved for multiple classes of games. In this talk I will present our results on the ridigity for the magic pentagram game, a simple binary constraint satisfaction game involving two players, five clauses and ten variables. In particular, we show that all near-optimal strategies for the pentagram game are approximately equivalent to a unique strategy involving real Pauli measurements on three maximally-entangled qubit pairs.</span></p><br>This talk is part of the following lists: <a href="https://talks.cs.umd.edu/lists/22">QuICS Seminar</a><br>