The Longest Distance In The World! Chinese Scientists Set New Record For 509 km of Fiber-optic Quantum Qommunications
On March 3rd, a reporter from Science and Technology Daily learned from the Jinan Institute of Quantum Technology that after the first experimental verification of the feasibility of long-distance dual-field quantum key distribution, after implementing a dual-field quantum key distribution experiment in a fiber of 300 kilometers in real environment, , Professor Wang Xiangbin and Researcher Liu Yang of the Jinan Institute of Quantum Technology cooperated with the academician Pan Jianwei of the University of Science and Technology of China again to realize the dual field quantum key distribution (TF-QKD) of 509 kilometers of real environment optical fiber. Related results have been published online in the international authoritative journal "Physical Review Letters" recently. Professor Wang Xiangbin and Professor Zhang Qiang are co-corresponding authors of the paper. This achievement successfully set a new world record for the longest transmission distance of quantum key distribution.
In the long-range practical application of quantum key distribution (QKD), channel loss is the most serious limiting factor. TF-QKD uses single-photon interference as an effective detection event, which makes the safe coding rate linearly decrease with the square root of the channel attenuation, and can even easily break the QKD coding rate linear limit without relay. However, the implementation conditions of TF-QKD are quite harsh, requiring single-photon-level interference of two remote independent lasers, and at the same time the accurate estimation of the relative phase fast drift of long-distance fiber links needs to be achieved through single-photon detection results.
The theoretical aspect of this achievement is based on the "send-not-send" dual-field quantum key distribution protocol proposed by Professor Wang Xiangbin, which greatly improves the system's tolerance to phase noise; in the experimental aspect, Professor Zhang Qiang's team adopted time-frequency transmission technology, The independent remote lasers have the same wavelength lock, and use the additional phase reference light to estimate the relative phase drift of the fiber, ensuring the safety properties of the measurement device. Finally, the QKD safe coding distance was successfully extended to 509 kilometers in the laboratory, breaking the absolute theoretical coding rate limit defined by the traditional non-relay QKD. At the same time, compared with other dual-field QKD experiments, the research has a unique advantage in terms of security: it is not only independent of the measurement equipment, but also fully considers the security under a limited code length. If the system repetition frequency is upgraded to 1GHz used in long-distance quantum communication networks such as the Beijing-Shanghai main line, the code rate can reach 5kbps at 300 kilometers, which will greatly reduce the number of trusted relays in backbone optical fiber quantum communication networks. Significantly improve the security of optical fiber quantum secret communication network.