509 kilometers!The team of Wang Xiangbin and Pan Jianwei set a new record for optical fiber quantum communication

The reporter learned from the Jinan Institute of Quantum Technology that following the first experiment to verify the feasibility of long-distance dual-field quantum key distribution, after the dual-field quantum key distribution experiment was realized in a 300-kilometer optical fiber in a real environment, Wang Xiangbin of Jinan Institute of Quantum Technology. Professor and researcher Liu Yang and the team of Academician Pan Jianwei from the University of Science and Technology of China collaborated again to realize the dual-field quantum key distribution (TF-QKD) of 509 kilometers of real-world optical fibers. The relevant results have been recently published online in the international journal “Physical Review Letters”. Professor Wang Xiangbin and Professor Zhang Qiang are the co-corresponding authors of the paper. This achievement successfully created a new world record for the longest transmission distance of quantum key distribution.

In the long-distance practical application of quantum key distribution (QKD), the channel loss is the most serious limiting factor. TF-QKD uses single-photon interference as an effective detection event, so that the safe coding rate decreases linearly with the square root of channel attenuation, and can even easily break through the linear limit of QKD coding rate in the absence of relays. However, the implementation conditions of TF-QKD are quite harsh, requiring single-photon-level interference of two long-range independent lasers, and at the same time, accurate estimation of the relative phase drift of long-distance fiber links 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 Wang Xiangbin, which greatly improves the system’s tolerance to phase noise; in terms of experiments, Zhang Qiang’s team used time-frequency transmission technology to connect two independent long-range lasers The wavelengths are locked to the same and additional phase reference light is used to estimate the relative phase fast drift of the fiber, ensuring the safety properties of the measurement device independent. Finally, the safe coding distance of QKD was successfully extended to 509 kilometers in the laboratory, breaking the absolute theoretical coding rate limit limited by traditional non-relay QKD. At the same time, compared with other dual-field QKD experiments, this study has a unique advantage in security: it is not only independent of measurement equipment, but also fully considers the security under limited code length. If the repetition rate of the system is upgraded to 1GHz used in long-distance quantum communication networks such as the Beijing-Shanghai trunk line, at a distance of 300 kilometers, the coding rate can reach 5kbps, which will greatly reduce the number of trusted relays in the backbone optical fiber quantum communication network. Significantly improve the security of the optical fiber quantum secure communication network.

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