First of its kind! my country's new breakthrough in quantum communication

Recently, Yuan Zhiliang's team at the Beijing Institute of Quantum Information Science used optical frequency comb technology to realize the first open-architecture dual-field quantum key distribution system and completed a 615-kilometer optical fiber quantum key distribution experiment. The relevant research results were published in the international academic journal Nature Communications on February 18, 2023.

Quantum key distribution is based on the basic principles of quantum physics and a one-time encryption method, which can achieve unconditional secure communication. In 2018, Toshiba Europe Research Institute in the UK proposed a new dual-field protocol, which makes the secure coding rate decrease linearly with the square root of the channel attenuation. It can break the code rate limit without relays and is a feasible solution for achieving optical fiber quantum communication over 500 kilometers. The implementation of the dual-field protocol requires two independent laser sources in different locations to achieve stable single-photon interference at a third-party remote node, but the slight frequency difference between the laser sources of the two communicating parties and the rapid phase drift 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 as a transmission medium between two distant locations, and then use time-frequency transmission or optical phase-locked loop and other technologies to complete the frequency locking of the laser sources in the two locations. This closed optical fiber architecture (see Figure a) is very unfavorable for multi-node wide-area quantum security network applications.

a) Traditional closed fiber architecture

b) Open architecture developed by Beijing Institute of Quantum Engineering

Based on the independently developed coherent sideband phase stabilization and remote laser source frequency calibration technology, Yuan Zhiliang's team has developed the first open architecture, new dual-field quantum key distribution system that does not require service fiber (see Figure b), achieving secure coding at the 400-kilometer, 500-kilometer, and 600-kilometer levels of low-loss optical fiber, breaking the code rate limit of relay-free quantum key distribution, and successfully demonstrated a quantum key distribution experiment with an arm length difference of 100 kilometers (the current record for the longest arm length difference).

Compared with previous experimental results, the phase drift rate of quantum signal light is reduced by more than 1,000 times, which greatly reduces the noise impact of phase reference light and helps to break through the distance of optical fiber quantum key distribution to the thousand-kilometer level. The open architecture based on optical frequency comb is conducive to the construction of multi-user and multi-node intercity quantum security networks in the future, and is of great significance to distributed quantum networks based on single-photon interference.

This work was supported by the National Natural Science Foundation of China.

Paper link:

https://www.nature.com/articles/s41467-023-36573-2

Source: "Beijing International Science and Technology Innovation Center" official account