1211.7171 (B. M. Sparkes et al.)

Gradient echo memory in an ultra-high optical depth cold atomic ensemble    [PDF]

B. M. Sparkes, J. Bernu, M. Hosseini, J. Geng, Q. Glorieux, P. A. Altin, P. K. Lam, N. P. Robins, B. C. Buchler

Quantum memories are an integral component of quantum repeaters - devices that will allow the extension of quantum key distribution to communication ranges beyond that permissible by passive transmission. A quantum memory for this application needs to be highly efficient and have coherence times approaching a millisecond. Here we report on work towards this goal, with the development of a $^{87}$Rb magneto-optical trap with a peak optical depth of 1000 for the D2 $F=2 \rightarrow F'=3$ transition using spatial and temporal dark spots. With this purpose-built cold atomic ensemble to implement the gradient echo memory (GEM) scheme. Our data shows a memory efficiency of $80\pm 2$% and coherence times up to 195 $\mu$s, which is a factor of four greater than previous GEM experiments implemented in warm vapour cells.

View original: http://arxiv.org/abs/1211.7171