Scientists propose and implement error tolerance for highly secure quantum key distribution

Professor Han Zhengfu of the team of academician Guo Guangcan of the University of Science and Technology of China and his collaborators Yin Zhenqiang, Wang Shuang, Chen Wei, etc., proposed an irrelevant quantum key distribution protocol for error tolerant measurement devices with high stability and high security, and confirmed from the aspects of security analysis and experimental verification that the protocol has a strong tolerance for non-ideal characteristics at the source end, which effectively promotes the practical application process of a new generation of quantum key distribution technology. The relevant research results were published online in Optics.


Error tolerant measurement device independent quantum key distribution experimental structure diagram

Information security is an important topic in today’s era, and quantum key distribution technology is based on quantum physical principles to achieve theoretically unconditionally secure key distribution. However, this theoretical security requires two important assumptions, namely that the user has the ideal device that conforms to the theoretical model description, and that eavesdroppers cannot hack into the probe and source ends of the system.

Measurement device-independent quantum key distribution is immune to all potential attacks against the probe end and is a typical protocol for the new generation of quantum key distribution technology. However, it still retains many security assumptions about the source, such as errors and noise in quantum state modulation that violate these security assumptions, which not only significantly reduce the performance of quantum key distribution systems, but also open up opportunities for potential eavesdroppers. In complex real-world environments, 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 introduces potential security issues.

In order to promote the practical application of the new generation of quantum key distribution technology, Han Zhengfu’s team proposed a measurement device-independent protocol with high stability and high security – error tolerant measurement device-independent protocol – by incorporating the common non-ideal characteristics of the source into the security proof framework. While the protocol eliminates all safety assumptions about the probe end, it also exempts the “single-photon state indistinguishable hypothesis” and the “pure state hypothesis” at the source end. By eliminating these two assumptions, the measurement device-independent protocol has a strong tolerance for signal distortion and noise in quantum state modulation.

After rigorous security analysis, the team proved that the non-ideal characteristics of these source-side devices do not break the security of the measurement device-independent protocol, nor do they reduce the security key generation rate of the system, so the error tolerance protocol has both high security and high stability.

Han Zhengfu’s team further built a measurement device-independent system to experimentally verify the proposed error tolerance protocol. The team first realized the original measurement device-independent protocol through the self-designed Sagnac-AMZI encoder and the four-strength decoy modulation device, and observed the change in the performance of the original protocol when the measurement modulation signal had different errors through the system. Subsequently, the team used the same system to execute an error-tolerant measurement device-independent quantum key distribution protocol, enabling secure key distribution at an almost constant rate without pre-calibrating the base selection signal.

Through the comparison of before and after performance, the high stability characteristics of the error tolerance measurement device independent protocol and the important value for practical applications are proved. Since actual 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. This achievement of Han Zhengfu’s team has greatly promoted the practical process of measuring device-independent quantum key distribution technology, and also laid a theoretical and experimental foundation for quantum key distribution technology to truly move towards unconditional security. (Source: China Science Daily Wang Min)

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