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 87Rb magneto-optical trap with a peak optical depth of 1000 for the D2 F=2→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±2% and coherence times up to 195 μs, which is a factor of four greater than previous GEM experiments implemented in warm vapour cells.
@article{arxiv.1211.7171,
title = {Gradient echo memory in an ultra-high optical depth cold atomic ensemble},
author = {B. M. Sparkes and J. Bernu and M. Hosseini and J. Geng and Q. Glorieux and P. A. Altin and P. K. Lam and N. P. Robins and B. C. Buchler},
journal= {arXiv preprint arXiv:1211.7171},
year = {2020}
}