It is learned from the official account of Beijing Institute of Quantum Information Science that recently, Yuan Zhiliang's team used optical frequency comb technology to realize an open-architecture dual-field quantum key distribution system for the first time, and completed a 615-kilometer fiber quantum key distribution experiment. While ensuring the security of quantum communication, this architecture can greatly reduce the cost of system construction and lay the foundation for the construction of multi-node wide-area quantum networks in China . international academic journal Nature-Communications.   

Quantum key distribution is based on the basic principles of quantum physics and one-time pad encryption, which can realize unconditional secure communication.  In 2018, the Toshiba European Research Institute in the UK proposed a new dual-field protocol, which makes the secure code rate decrease linearly with the square root of the channel attenuation, and can break through the code rate limit without relays. It is a feasible solution for realizing optical fiber quantum communication over 500 kilometers .

The realization of the dual-field protocol requires two independent laser sources in different places to achieve stable single-photon interference at the third-party remote node, but the small frequency difference of the laser sources of the two communication parties and the rapid phase shift caused by the long-distance optical fiber have an important impact on the interference. .  At present, the traditional solution is to set up a service optical fiber between two distant places as the transmission medium, and then use time-frequency transmission or optical phase -locked loop technology to complete the frequency locking of the laser sources in the two places. This closed optical fiber architecture (see Figure a) It is very unfavorable for multi-node wide-area quantum security network applications.

a) Traditional closed optical fiber architecture; b) Open architecture developed by Beijing Quantum Institute

Based on the self-developed coherent sideband phase stabilization and off-site laser source frequency calibration technology, Yuan Zhiliang's team developed the first new dual-field quantum key distribution system with an open architecture and no service fiber (see Figure blow), realizing -loss fiber 400-kilometer, 500-kilometer, and 600-kilometer security coding, and break the code rate limit of non-relay quantum key distribution, and successfully demonstrated the quantum key distribution experiment with an arm length difference of 100 kilometers ( The current longest arm length difference record).

Compared with the previous experimental results, the phase drift rate of the quantum signal light is reduced by more than 1000 times, which greatly reduces the noise influence of the phase reference light, and helps the optical fiber quantum key distribution distance to break through to the thousand-kilometer level.  The open architecture based on optical frequency comb is conductive to the construction of multi-user and multi-node intercity quantum security network in the future, and is of great significance to the distributed quantum network based on single photon interference.