The University of Science and Technology of China successfully integrated long-distance quantum key distribution and fiber optic vibration sensing

Recently, Pan Jianwei, Zhang Qiang, etc. of the University of Science and Technology of China cooperated with Wang Xiangbin and Liu Yang of the Jinan Institute of Quantum Technology to realize a set of experimental systems that integrate quantum key distribution and optical fiber vibration sensing, and realized 658 km long-distance optical fiber sensing while completing the optical fiber double field quantum key distribution (TF-QKD), with a positioning accuracy of 1 km, which greatly broke through the limitation that the distance of traditional optical fiber vibration sensing technology is difficult to exceed 100 km. The research was published in the Form of “Editor’s Recommendation” in the Physical Review Letters and reported by Physics, a website of the American Physical Society (APS).

Optical fiber vibration sensing with optical fiber as a sensor for vibration sensing, through the use of a single optical fiber simultaneously to achieve vibration monitoring and signal transmission, due to the advantages of high sensitivity, fast response, simple structure, uniform distribution, etc., in the structural health monitoring, oil and gas pipeline leakage monitoring, perimeter protection and seismic monitoring and other engineering fields have a wide range of application prospects, so it has attracted widespread attention and research. At present, optical fiber vibration sensing mostly uses distributed sound wave sensing technology, and its sensing distance is limited to less than 100 kilometers, and an important technical challenge is how to overcome the distance limit and achieve long-distance optical fiber vibration sensing.

Quantum key distribution (QKD) is based on the basic principles of quantum mechanics, combined with the encryption method of “one secret at a time”, which can achieve unconditionally secure and confidential communication. Because of its important practical significance, QKD has been a research hotspot in the international academic community for decades. The TF-QKD protocol proposed in 2018 can break through the linear limit of QKD bit rate and is considered to be the best solution to achieve ultra-long-distance optical fiber QKD. However, the TF-QKD technology is quite demanding, requiring single-photon interference from two remote independent lasers, a slight deviation in the frequency of the light source, and any fluctuation in the fiber optic link that accumulates phase noise and reduces the quality of the single-photon interference.

In practical applications, noise such as sound and vibration along the fiber link are inevitable, so it is necessary to detect the phase change of the fiber caused by environmental noise in real time during the TF-QKD experiment and compensate for it in real time or after data processing. In general, information about these phase changes is discarded after the QKD experiment is completed. But in fact, this “redundant” information reflects real-time phase changes in the transmitted light in the fiber, which may come from vibration disturbances or temperature drift along the fiber link. By analyzing these phase change information, combined with some characteristics of vibration, vibration information can be obtained and positioned, so as to achieve ultra-long-distance fiber vibration sensing.

Based on the “send” or “do not send” TF-QKD (SNS-TF-QKD) protocol proposed by Wang Xiangbin of Jinan Institute of Quantum Technology, Pan Jianwei and Zhang Qiang’s research group used key technologies such as time-frequency transmission to accurately control the frequency of two independent lasers, and cooperated with Chen Yang and Zhao Dongfeng of the University of Science and Technology of China to use additional phase reference light to estimate the relative phase rapid drift of the optical fiber, and restored the external disturbance generated by the artificial controllable vibration source loaded on the optical fiber channel. Combined with the high-count rate and low-noise single-photon detector developed by the Yulixing team of the Shanghai Institute of Microsystems of the Chinese Academy of Sciences, the 658 km fiber double-field quantum key distribution and fiber vibration sensing were finally realized, and the disturbance position of the artificial vibration source on the link was located, and the accuracy was better than 1 km.

The above research results show that the TF-QKD network architecture can not only realize the distribution of security keys over ultra-long distances, but also be applied to ultra-long-distance vibration sensing, and realize the fusion of wide-area quantum communication network and optical fiber sensing network.

The first authors of this research paper are Chen Jiupeng and Zhang Chi, doctoral students of the University of Science and Technology of China.

Thesis Link:https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.180502

Physics reporting links:https://physics.aps.org/articles/v15/63

The work was supported by the Ministry of Science and Technology, the Natural Science Foundation of China, the Chinese Academy of Sciences, Shandong Province and Anhui Province.
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