Quantum memory will play an important role in quantum networks, notably as components in quantum repeaters. One promising technique for realizing broadband quantum memory, the atomic frequency comb (AFC) protocol, calls for a material with large inhomogeneous broadening and small homogeneous broadening: spectral-hole burning techniques can be used to prepare the absorption spectrum in a periodic pattern of narrow peaks (an AFC). A single photon, absorbed as a collective excitation, will be re-emitted after a time interval fixed by the AFC tooth spacing. On-demand retrieval can also be realized by using control pulses to implement spin-wave storage.

Rare-earth-doped crystals like Pr3+:Y2SiO5 are well-suited to the AFC protocol. However, in many cases the materials have hyperfine structure that limits AFC bandwidth. Here, we present an experiment showing that it is possible to work within these constraints to generate broadband AFCs.

(Pizza and refreshments will be served after the talk.)