Professor Han Zhengfu, a team of academicians guo Guangcan of the University of Science and Technology of China, and his collaborators Wang Shuang, Yin Zhenqiang, He Deyong, Chen Wei, etc., recently realized the distribution of quantum keys for 833 kilometers of optical fiber, increasing the secure transmission distance world record by more than 200 kilometers, and taking an important step towards the realization of thousand kilometers of land-based quantum secure communication. The results were published online on January 17 in Nature Photonics.
Quantum key distribution is based on the basic principles of quantum physics and provides a means of eavesdropping and perceivable key distribution at the level of information security. Optical quantum is a natural carrier of quantum information, but the inevitable loss in the line limits the security 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 security distance of direct transmission of optical quantum key distribution has become one of the most challenging difficulties and focuses at present.
In 2018, the two-field quantum key distribution protocol proposed by British scientists broke through the original theoretical limits, but the improvement of its theory and the development of experimental technology were extremely challenging. In 2019, the research team of Guo Guangcan and Han Zhengfu first proposed a two-field class protocol selected after phase-free, and for the first time verified the feasibility of such a protocol in a 300-kilometer fiber channel.
After more than 2 years of exploration, Guo Guangcan and Han Zhengfu's team proposed an improved four-phase modulation dual-field protocol, and further improved the key technologies such as phase-locked frequency stabilization technology, high-bandwidth channel phase compensation technology, and single-photon detection signal screening technology with high signal-to-noise ratio, and extended the secure transmission distance of optical fiber double-field quantum key distribution to 833 kilometers.
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, which is an important step to realize the land-based wide-area quantum secure communication network of thousands of kilometers.
![Quantum Secure Communication: Making Communication More Secure | informal science[fig]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)