For quantum computers to achieve their promise, regardless of the qubit technology, significant improvements to both performance and scale are required.  Quantum-dot-based qubits in silicon have recently enjoyed dramatic advances in fabrication and control techniques.  The “exchange-only” modality is of particular interest, as it avoids control elements that are difficult to scale such as microwave fields, photonics, or ferromagnetic gradients.  In this control scheme, the entirety of quantum computation may be performed using only asynchronous, baseband voltage pulses on straightforwardly tiled arrays of quantum dots.  The pulses control only a single physical mechanism, the exchange interaction, which exhibits low control crosstalk and exceptionally high on/off ratios. Exchange enables universal logic within a qubit encoding that is robust against certain correlated errors.  These aspects collectively provide a compelling path toward fault-tolerance.  HRL Laboratories has recently demonstrated universal quantum logic of encoded exchange-only Si spin qubits, including two-qubit gates performed on arrays of six quantum dots.  In this seminar, we will introduce the fabrication and operation principles of these encoded Si qubit devices, and we will show recent experimental results.

References: 

1. Encoded 2-qubit gate: https://arxiv.org/abs/2202.03605

2. State preparation and measurement: https://arxiv.org/abs/2112.09801 [https://journals.aps.org/prxquantum/abstract/10.1103/PRXQuantum.3.010352]

3. Device Design and Fab: https://arxiv.org/abs/2107.10916  [https://pubs.acs.org/doi/10.1021/acs.nanolett.1c03026 ]

11:00 am - 12:00 pm ET (discussion time with students/postdocs interested in HRL Laboratories)

Host: Kartik Srinivasan