China News Agency, Hefei, January 19 (Reporter Wu Lan) The reporter learned from the University of Science and Technology of China on the 19th that Professor Han Zhengfu and his collaborators, the team of academician Guo Guangcan of the school, have recently achieved 833 kilometers of optical fiber quantum key distribution, which will be safely transmitted. The distance world record has been improved by more than 200 kilometers, and an important step has been taken towards the realization of 1,000-kilometer ground-based quantum secure communication.

　　The results were recently published online in Nature Photonics.

　　Quantum key distribution is based on the basic principles of quantum physics, and provides an eavesdropping-perceived key distribution method at the level of information security.

Light quantum is the natural carrier of quantum information, but the inevitable loss in the circuit limits the safe distance of quantum key distribution, and is also one of the key factors restricting the deployment and application of wide-area quantum secure communication networks.

Therefore, how to extend the safe distance of direct optical quantum key distribution has become one of the most challenging difficulties and focuses at present.

　　In 2018, the dual-field quantum key distribution protocol proposed by British scientists broke through the original theoretical limit, but the perfection of its theory and the development of experimental technology are extremely challenging.

In 2019, the research groups of Guo Guangcan and Han Zhengfu first proposed a dual-field protocol with phase-free selection and verified the feasibility of such a protocol in a 300-kilometer fiber channel for the first time.

　　After more than 2 years of exploration, the research team proposed an improved four-phase modulation dual-field protocol, and further improved key technologies such as phase-locking and frequency-stabilizing technology of independent light sources, extending the secure transmission distance of optical fiber dual-field quantum key distribution to 833 kilometers.

　　Compared with the work of other research teams at home and abroad, this achievement not only greatly increases the optical fiber quantum key distribution distance from more than 500 kilometers to 833 kilometers, but also increases the security code rate by 50 to 1000 times. An important step forward in quantum secure communication networks.

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