Towards high-speed optical quantum memories

K. F. Reim, J. Nunn, V. O. Lorenz, B. J. Sussman, K. C. Lee, N. K. Langford, D. Jaksc & I. A. Walmsley

Quantum memories, capable of controllably storing and releasing a photon, are a crucial component for quantum computers¹ and quantum communications². To date, quantum memories^{3, 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 field^{7, 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.

**Groupmeeting by Amir Feizpour, June 16th, 2010**