Scientists verify the feasibility of quantum-key distribution independent of space-ground measurement devices

Recently, Academician Pan Jianwei of the University of Science and Technology of China, Peng Chengzhi, Cao Yuan, etc., together with Professor Wang Xiangbin of Tsinghua University, You Lixing, researcher of Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, and others cooperated to realize the free space-optical hybrid quantum key distribution network experiment independent of long-distance measurement equipment for the first time in the world, and completed the verification of high background noise conditions during the day and satellite-ground Doppler shift compensation. On September 6, the results were published online in Physical Review Letters. This achievement comprehensively verifies the feasibility of satellite-ground measurement equipment-independent quantum key distribution, and takes an important step towards a satellite-based global and high-security quantum communication network.

Experimental device diagram Photo courtesy of China University of Science and Technology

The measurement device-agnostic quantum key distribution protocol uses two-photon interferometry technology to eliminate all security vulnerabilities at the detection end without making any security assumptions about the quantum devices at the measurement end, and is considered one of the best candidates among various quantum key distribution protocols. The use of free space channels and satellites is currently the most effective way to achieve a global quantum communication network. In 2020, the experimental team extended the protocol to free space channels for the first time in the world through the development of technologies such as independent light source frequency locking, independent clock synchronization, and adaptive optics against strong turbulence.

In this research work, the experimental team further explored the potential of the measurement device-independent quantum key distribution protocol and explored the feasibility of extending it to satellite platforms. In order to realize the practical application of satellite-ground measurement equipment-independent quantum key distribution network, it is necessary to overcome the difficulties of free space and optical fiber networking, high background noise during the day, and Doppler frequency shift. First, quantum interferometry can be used as a natural star network node, which is very convenient to connect free space and fiber channels. The experimental team demonstrated the free-space-fiber interface and star network topology by constructing multiple transmitters and channels, combined with adaptive optics technology and single-mode fiber coupling. At the same time, the experimental team revealed for the first time that compliance detection based on two-photon interference can make the measurement device-independent quantum key distribution protocol obtain great tolerance for background noise, and realize the experimental demonstration of measurement device-independent quantum key distribution under the background of strong daylight at noon.

Furthermore, in the face of high-speed relative motion between the satellites and the ground, the experimental team simulated and compensated for the Doppler shift during satellite transit, improving the visibility of HOM interference throughout the whole process to close to the theoretical limit. Through these experimental studies, the experimental team comprehensively verified the feasibility of independent quantum key distribution of satellite-ground measurement equipment, laying a solid foundation for the construction of a space-ground integrated and high-security quantum communication network in the future. (Source: Wang Min, China Science News)

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