USTC implements fully passive quantum key distribution

The team of Academician Guo Guangcan of the University of Technology of China has made important progress in the research of quantum key distribution. The team Han Zhengfu, Wang Shuang, Yin Zhenqiang, Chen Wei and their collaborators proposed a new quantum key distribution implementation scheme without active modulation, and completed experimental verification, which provides a new idea for realizing a highly realistic and secure quantum key distribution system. On September 13, the results were published in Physical Review Letters.

Fully passive quantum key distribution experimental system Photo courtesy of China University of Science and Technology

Quantum key distribution theoretically enables unconditionally secure key sharing. However, factors such as device characteristics, modulation accuracy, and environmental interference may cause realistic security problems in the system. For example, Guo Guangcan’s team found that lithium niobate active modulation devices, which are widely used in the system, may be subject to side-channel attacks such as optical refraction and leak information.

In order to completely solve the hidden dangers caused by active modulation, Guo Guangcan’s team and collaborators found a different way to design a quantum key distribution system that does not require active modulation. The system scheme overcomes the contradiction that “passive” light emphasis system and quantum state coding cannot be realized at the same time, and gives a strict security key rate considering the “finite length effect”. The team solved the problem of channel environment interference through fully passive timestamp-phase coding, and solved the problem of excessive data throughput through optimized selection strategy, and finally completed a quantum key distribution system without any active modulation, verifying the security and feasibility of fully passive quantum key distribution.

Security is a core value and requirement for quantum key distribution. Exploring protocols with higher real-world security and designing corresponding schemes and systems is one of the keys to advancing quantum key distribution to practical use. According to the researchers, this study provides a new idea for realizing a highly realistic and secure quantum key distribution system, which is of great significance for promoting the practical application and standardization of this field. (Source: Wang Min, China Science News)

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