Highly efficient and long-lived optical quantum memory with cold atoms

Quantum memory is an essential element for long distance quantum communication and photonics quantum computation protocols. The practical implementation of such protocols requires an efficient quantum memory with long coherence time. Here, we report a highly efficient coherent optical memory via the gradient echo memory (GEM) technique in cold atoms. The efficiency is as high as 87% with the e
^-1
coherence time of 1 ms. The ability of quantum storage is verified using heterodyne tomography of small coherent states, showing that our system performs in the quantum regime.