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Chinese scientists achieved quantum key distribution over thousands of kilometers of unrepeated optical fibers, setting a world record



News from IT House on May 27, IT House learned from the University of Science and Technology of China that Pan Jianwei and Zhang Qiang of the school cooperated with Wang Xiangbin of Tsinghua University, Liu Yang of Jinan Institute of Quantum Technology, and You Lixing and Zhang Weijun of Shanghai Institute of Microsystems, Chinese Academy of Sciences. , by developing technologies such as low-crosstalk phase reference signal control and extremely low-noise single-photon detectors, the 1002-kilometer point-to-point long-distance quantum key distribution in optical fibers has been realized.It not only set a world record for the distance of quantum key distribution without relays in optical fibers, but also provided a solution for high-speed backbone links of intercity quantum communication. Relevant research results were published in the international academic journal Physical Review Letters on May 25.

Quantum key distribution (QKD) is based on the basic principles of quantum mechanics, which can carry out secure key distribution among users, combined with the “one-time pad” encryption method, and then realize the highest security confidential communication. However, the distance of quantum key distribution has been limited by factors such as the inherent loss of communication fibers and detector noise. The two-field quantum key distribution (TF-QKD) protocol uses the characteristics of single-photon interference to increase the relationship between the coding rate and the distance from the linear relationship of general quantum key distribution to the level of the square root, so it can obtain far more than the general quantum key. The yardage distance of the distribution scheme.

In this work, the research team adopted the “send-not-send” dual-field quantum key distribution protocol proposed by Wang Xiangbin et al., which can effectively improve the working distance of the quantum key distribution system under realistic conditions. In order to carry out extremely long-distance quantum key distribution, the research team cooperated with YOFC Co., Ltd. to adopt ultra-low loss optical fiber based on “pure silica core” technology to achieve a quantum channel of less than 0.16 dB/km fiber optic link. The Shanghai Institute of Microsystems, Chinese Academy of Sciences has developed an extremely low-noise superconducting single-photon detector, which reduces the noise of the single-photon detector to 0.02 cps by suppressing the dark counts caused by thermal radiation through multi-stage filtering in the 40 K and 2.2K temperature regions. The research team also developed a time-division multiplexed dual-wavelength phase estimation scheme, which avoids the influence of noise such as secondary Rayleigh scattering of the same wavelength reference light and spontaneous Raman scattering of different wavelength reference light, and reduces the link noise to below 0.01 Hz.

Figure 1: Schematic diagram of the long-distance quantum key distribution experiment system

On the basis of the above-mentioned technical development, this work realizes the double-field quantum key distribution with the longest distance of 1002 km, and obtains a coding rate of 0.0034 bps. After optimizing the system parameters, a coding rate of 47.06 kbps was obtained at a fiber distance of 202 km, and at a fiber distance of 300 km and 400 km, the obtained coding rate was improved by 6 compared with the original “measurement device independent” quantum key distribution. order of magnitude.This work not only verified the feasibility of the double-field quantum key distribution scheme under extremely long distances, but also verified that under the distance of inter-city optical fiber, the protocol can realize quantum key distribution with high coding rate, which is suitable for inter-city quantum communication Backbone link use. This work was highly praised by the reviewers, who considered this work to be “an extremely important progress in this field, a significant advance for the field and a new landmark for QKD technology”.

Figure 2: The code rate results of the long-distance quantum key distribution experiment

This research work has been funded by the Ministry of Science and Technology, the Natural Science Foundation of China, the Chinese Academy of Sciences, Shandong Province, Anhui Province and Shanghai Municipality.

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