Some Asymmetric Issues In Practical Quantum Key Distribution System

In the 21st century,information security is the undoubtedly important.However,the current classical cryptography security is facing a huge threat.On the contrary,quantum key distribution(QKD)can offer theoretical unconditional security ensured by the law of physics,which is different from classic cryptography based on the per-ceived intractability of high computational complexity.Any eavesdropping would be exposed by introducing the observable error.Since proposal of the first QKD protocol:the so-called BB84 protocol presented in IEEE international conference on comput-ers,significant process was made in both theoretically and experimentally in the three decades that followed.Nonetheless,there is still a huge gap between reality and theory.The practical application process of QKD still suffer from the device imperfections of the realistic implementations.This thesis focuses on the researches in the practical application of QKD and introduces the research productions of the author during my PhD program,in-cluding the asymmetric problem of quantum key distribution scheme and experimental Twin-field quantum key distribution protocol(TF-QKD).Specifically,we design and experimentally demonstrate the implementation of high-rate BB84 with asymmetric basis detector efficiency by using the recent 4-intensity decoy-state optimization protocol proposed by Xiang-Bin Wang group of Tsinghua Uni-versity.The results not only provide a higher key rate than previous protocols with unbiased bases,but also rule out an implicit assumption in QKD that the efficiency of Z basis and X basis are restricted to be the same.This work paves the way towards a more practical QKD setting.In addition,we introduce the measurement-device-independent quantum key dis-tribution(MDI-QKD)protocol,which can eliminate all detector side channels.We demonstrate high key rate for MDI-QKD in the situation of large channel asymme-try by using the recent 7-intensity decoy-state optimization protocol proposed by Hoi-Kwong Lo group of University of Toronto.The results have moved MDI-QKD to-wards widespread applications in practical network settings,where the channel losses are asymmetric and user nodes can be dynamically added or deleted.At last,we introduce TF-QKD protocol and the key technologies of the implemen-tation.We design and develop an TF-QKD system with high-rate,high performance and high stability.By using the laser injection technique and the phase post-compensation method,we demonstrate the TF-QKD over more than 500 km optical fiber.This work represents a significant step toward long-distance quantum communication for the fu-ture quantum internet.