Towards high-speed optical quantum memories

Quantum memories, capable of controllably storing and releasing a photon, are a crucial component for quantum computers1 and quantum communications2. To date, quantum memories3,4,5,6 have operated with bandwidths that limit data rates to megahertz. Here we report the coherent storage and retrieval of sub-nanosecond low-intensity light pulses with spectral bandwidths exceeding 1 GHz in caesium vapour. The novel memory interaction takes place through a far off-resonant two-photon transition in which the memory bandwidth is dynamically generated by a strong control field7,8. This should allow data rates more than 100 times greater than those of existing quantum memories. The memory works with a total efficiency of 15%, and its coherence is demonstrated through direct interference of the stored and retrieved pulses. Coherence times in hot atomic vapours are on the order of microseconds9, the expected storage time limit for this memory. Quantum memories for storing and releasing photons are required for quantum computers and quantum communications. So far, their operational bandwidths have limited data-rates to megahertz. Researchers now demonstrate coherent storage and retrieval of subnanosecond low-intensity light pulses with spectral bandwidths exceeding 1 GHz.