Shulou(Shulou.com)11/24 Report--

Thank you, Mr. Air, a netizen of CTOnews.com, for your clue delivery! CTOnews.com March 9 news, CTOnews.com learned from the Beijing Institute of Quantum Information Science official account that recently, Yuan Zhiliang's team, using optical frequency comb technology, implemented an open architecture two-field quantum key distribution system for the first time, and completed a 615km optical fiber quantum key distribution experiment. This architecture can not only ensure the security of quantum communication, but also greatly reduce the construction cost of the system, and lay the foundation for the construction of multi-node wide area quantum network in our country. The relevant results were published in the international academic journal Nature Communications a few days ago.

Based on the basic principles of quantum physics and one encryption at a time, quantum key distribution can realize unconditional secure communication. In 2018, Toshiba Europe Research Institute proposed a new dual-field protocol, which makes the security bit rate linearly decrease with the square root of channel attenuation, and can break through the rate limit without relay, which is a feasible scheme to realize optical fiber quantum communication of more than 500 kilometers.

The implementation of the dual-field protocol requires two independent laser sources to achieve stable single-photon interference at the third-party remote node, but the small frequency difference of the laser sources on both sides of the communication and the fast phase drift caused by long-distance optical fiber have an important impact on the interference. At present, the traditional scheme is to set up a service fiber as a transmission medium between the two places, and then complete the frequency locking of the laser sources in the two places through time-frequency transmission or optical phase-locked loop (OPLL). This closed optical fiber architecture (see figure a) is very unfavorable to the application of multi-node wide area quantum secure network.

A) traditional closed fiber architecture B) based on the self-developed coherent sideband phase stabilization and remote laser source frequency calibration technology developed by Yuan Zhiliang's team of Beijing Quantum Institute, a new dual-field quantum key distribution system with open architecture and no service fiber is developed (see figure b), which realizes the secure coding of 400 km, 500 km and 600 km of low-loss optical fiber, and breaks the code rate boundary of non-relay quantum key distribution. The quantum key distribution experiment with arm length difference of 100 kilometers (currently the longest arm length difference record) is also successfully demonstrated.

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

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