Experimental Study On Practical Quantum Communication Systems And Their Security

Quantum communication,whose security is based on the quantum theory rather than the computational complexity,can theoretically achieve an uncondi-tional level secuirty.However,the model of practical system can not perfectly match the theoretical model,and with as the complexity of the actual sysytem increases,these differences will become more apparent.Eventally,loopholes available to eavesdroppers can be exploited to weaken the security of the actual sysytem.With the gradual implementation of quantum communication technol-ogy,the security of practical sysytem has received extensive attention.Some attack schemes and improvement protocols for actual systems have also been proposed and discussed.The study of attack and defense in quantum communi-cation is like the yin and yang in the Taiji diagram,this will promote the further development of this technology.This thesis mainly studies the security of the practical quantum commu-nication system from the aspects of studying actual system vulnerabilities and reducing its complexity.The main research contents are summarized as fol-lows:The problem of the degree of freedom of implementation of quantum secret sharing protocol in practical systems is studied.Based on the circular quantum secret sharing protocol,a single-photon group dynamic scheme is proposed.Users in the network can be divided into different groups according to certain characteristics.The boss Alice can realize the choice of secret sharing groups through polarization multiplexing.In addition,through a single distribution,Alice can also share secrets independently with multiple teams.Therefore,the group dynamic scheme further increases the flexibility of quantum secret shar-ing and expands the usage scenarios of the protocol.For the detector-device-independent quantum key distribution protocol,we discuss the ineffectiveness of the detector wavelength-related attack on the actual system.Based on the famous detector blinding attack scheme,we pro-pose a new eavesdropping strategy,in which we described how to effectively blind all detectors and how to effectively control the detector response in detail.In order to verify the feasibility of the attack scheme,we carried out a principled experimental verification and found that the detectors can be perfectly blinded,and only one of them can be effectively controlled to respond.In order to reduce the complexity of the actual quantum key distribution system,we studied the reference-frame-independent protocol,which can ef-fectively avoid the additional consumption of resources in the reference frame calibration process.By using the convex optimization method to estimate the eavesdropper's information,we efficiently reduced the quantum states required for state preparation from six to three,and the security of the this simplified protocol under coherent attacks was also proved.In order to verify the practi-cal feasibility of fewer states protocols,we carried out experimental verification at a transmission distance of 15 km and 55 km.It turns out that reducing the number of quantum states does not have a large impact on the security key rate.We further experimentally studied the feasibility of the reference frame and measurement device independent quantum key distribution protocol at high system frequency and long transmission distance.In the system construction,a high-efficiency coding unit is designed.The phase modulation can be used to realize the preparation of different quantum states,and the time information of the photons is multiplexed with the polarization information to achieve efficient recognition of the two Bell states.Finally,a transmission distance of more thatn 100 km is achieved with a system frequency of 50 MHz.