Twin-field Quantum Key Distribution Over Free-space Optical Channels In The Presence Of Atmospheric Turbulence

Quantum key distribution provides theoretic information security based on the laws of quantum physics.Two legitimate sites of key distribution can exchange secret keys even in the presence of eavesdropper.Since the heuristic BB 84 protocol has been proposed,albeit impressive progress have been achieved either in developing new QKD protocols or improving practical system performance and security.The security threats mainly stem from the imperfections of single photon sources and detectors.The decoy state QKD and MDI-QKD protocol have been proposed against the security issues at source and detector side,respectively.However,there is a fundamental limit on the key rate versus channel transmittance for point-to-point repeaterless QKD protocols over lossy quantum channels.Fortunately,the PLOB bound has been lifted by the proposition of twinfield QKD protocol in 2018.Future quantum communication networks envisaged on a global scale will include various networks interlinked via optical fiber and free space channels.In recent years,QKD protocol based on optical fiber has been extensively studied.TF-QKD may enable 550 km QKD using standard optical fiber without quantum repeaters.However,the performance of TF-QKD in free-space channel is still unclear.In this paper,a free-space channel model is proposed with specific turbulence characterization discussed.Here,the key rate of TF-QKD under multiple scenarios considering the variation of turbulence and different link configuration is investigated.Simulation results demonstrate that the performance of free-space TF-QKD is related to link configuration and turbulence motion which is determined by surface feature,time and height.Furthermore,TF-QKD protocol is a potential scheme for the free-space quantum communication.The first two chapters of mainly discuss the background and significance,the research progress of QKD and basic protocols,which leads to the research of TF-QKD protocol,then summarize the principle of TF-QKD protocol and the calculation method of secure key rate,especially the PM-QKD protocol.The 3rd chapter is the study of the free space quantum channel,integrating various attenuation factors,especially the influence of atmospheric turbulence,to obtain a simulation model.In Chapter 4,the performance of free space TF-QKD is simulated and compared after formula discussion and parameter estimation.