Quantum communication is the art of transferring a quantum state from one place to another. It holds ultra-high security as a quantum photon can neither be separated nor duplicated. Direct transmission is limited to moderate distances (less than 500 km) due to the exponential decay of photons and the solution could be the quantum repeater.

The quantum repeater, as the amplifier stations, will extend the communication range by amplify the light signals. One attractive strategy for realizing quantum repeaters is based on the use of atomic ensembles as quantum memories.

The team led by PAN Jianwei and BAO Xiaohui from University of Science and Technology of China of Chinese Academy of Sciences has developed a high-performance light-matter interface, which fulfills a quantum repeater with both efficiency and a lifetime for the first time. This work will have a variety of applications in the long-distance quantum communication in the near future. This study was published in Nature Photonics entitled "An efficient quantum light–matter interface with sub-second lifetime."

In 2012, PAN's team has presented an efficient quantum memory with mm-second lifetime, which is a factor of 10000 times higher than the duration of pulsed optical operations [Nature Physics 8, 517–521 (2012)].

In order to improve the duration to realize long-distance transmission, PAN's team used a three-dimensional (3D) optical lattice to confine an atomic ensemble inside a ring cavity. The results of a lifetime being 0.22 second and the initial retrieval efficiency being 76% were achieved. The total efficiency has been promoted by two orders of magnitude.

This work will help to realize quantum communication to distance of more than 500 km and even 1000 km in some situation. The referee highlights this work as "extraordinary tour de force".

The research is supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences, and the National Fundamental Research Program of China.

Figure: Experimental set-up and atomic levels (Image by BAO Xiaohui)