Guo Guangcan's team at CSU proposes and implements error-tolerant, highly secure quantum key distribution
The Key Laboratory of Quantum Information of the Chinese Academy of Sciences, led by academician Guo Guangcan of the Chinese University of Science, has made important progress in the practical study of high-security quantum key distribution. Prof. Zhengfu Han and his collaborators Zhenqiang Yin, Shuang Wang and Wei Chen have proposed an error-tolerant measurement device-independent quantum key distribution protocol with high stability and security, and confirmed from both security analysis and experimental verification that the protocol is extremely tolerant to non-ideal characteristics at the source, which strongly promotes the practicalization of next-generation quantum key distribution technology. The related research results were published online in the internationally renowned academic journal Optica on August 3 [Optica9,886-893 (2022)].
Information security is an important theme of our time, and quantum key distribution technology is based on the principles of quantum physics, which can achieve theoretically unconditionally secure key distribution. However, this theoretical security requires two important assumptions, i.e., that the user has an ideal device that fits the description of the theoretical model and that an eavesdropper cannot penetrate the detection and source sides of the system. Measurement device-independent quantum key distribution is immune to all potential attacks against the probe side and is a typical protocol for the next generation of quantum key distribution technology. However, it still retains many security assumptions on the source side, for example, errors and noise in quantum state modulation can violate these security assumptions, which not only significantly degrade the performance of the quantum key distribution system, but also give potential eavesdroppers an opportunity to take advantage of it. In a complex real-world environment, users have to spend a lot of resources to monitor and calibrate the source side, which not only reduces the efficiency of protocol execution, but also may bring potential security problems.
To advance the practical application of next-generation quantum key distribution technology, Han Zhengfu's team proposes the error-tolerant measurement device-independent protocol, which combines high stability and high security, by incorporating the common non-ideal characteristics of the source end into the security proof framework. The protocol dispenses with all safety assumptions on the probe side, and also dispenses with the "single photon state indistinguishability assumption" and "pure state assumption" on the source side. By dispensing with these two assumptions, the measurement device-independent protocol is extremely tolerant of signal distortion and noise in quantum state modulation. After rigorous security analysis, the team demonstrated that the non-ideal characteristics of these source devices do not undermine the security of the measurement device-independent protocol and do not degrade the secure key generation rate of the system, so the error-tolerant protocol is both highly secure and highly stable.
Han Zhengfu's team further builds a measurement device-independent system to experimentally verify the proposed error-tolerant protocol. The team first implemented the original measurement device-independent protocol with a self-designed Sagnac-AMZI encoder and a four-strength decoy state modulation device, and observed the performance of the original protocol with different errors in the measurement modulation signal through this system. The team then used the same system to implement an error-tolerant measurement device-independent quantum key distribution protocol to achieve secure key distribution at an almost constant rate without pre-calibration of the chosen base signal.
The before-and-after performance comparison demonstrates the high stability characteristics of the error-tolerant measurement device-independent protocol and its important value for practical applications. Since practical quantum key systems often need to work in complex and fast-changing environments, it is difficult to achieve accurate real-time calibration at the source end. This result of Han Zhengfu's team greatly advances the practicalization of measurement device-independent quantum key distribution technology and lays the theoretical and experimental foundation for quantum key distribution technology to truly move toward unconditional security.
Figure 1. Experimental structure of error-tolerant measurement device-independent quantum key distribution
The co-first authors of the work are Feng-Yu Lu, a postdoctoral fellow at the Key Laboratory of Quantum Information, Chinese Academy of Sciences, and Ze-Hao Wang, a doctoral student. Prof. Zhenqiang Yin and Prof. Shuang Wang are the co-corresponding authors of the work. This work was supported by grants from the Ministry of Science and Technology, the National Natural Science Foundation of China, the China Postdoctoral Science Foundation, the Chinese Academy of Sciences, and Anhui Province.
Link to article：
https://doi.org/10.1364/OPTICA.454228
