Several Theoretical And Experimental Studies On Quantum Communication

With the development of science and technology,information security is gradually threatened by eavesdroppers in the process of classical communication.Fortunately,quantum communication based on the principle of quantum mechanics enables users to achieve unconditional and secure communication over long distances.Quantum communication plays an important role in expanding multi-user networking,improving the fault tolerance of communication systems,extending channel distances,and defending against security breaches.In the past 30 years,quantum communication obtains great progress in theory and experiment.This thesis focuse on several theories and experimental research in quantum communication systems.The main research contents are following:A feasible scheme is proposed to automatically compensate the phase fluctuation and polarization evolution of fiber channels between long-distance communication users.The experimental device can be applied to the multi-user twin-field quantum key distribution protocol,which automatically compensates the phase fluctuation of the two fields during transmission.It overcomes the main challenge of the twin-field quantum key distribution protocol in practical implementation,which requires long-distance subwavelength path-length phase stability.Furthermore,the simple and stable structure is easily extended to multi-user quantum key distribution network and more flexible by combining with polarization multiplexing.This thesis further studies the security of the quantum digital signature protocol in the case of multi-party and the redundancy of the required quantum link.A multi-party ring quantum digital signature scheme is proposed,which innovatively utilizes innovatively random sampling instead of symmetric operation.Moreover,an experimental device of the random sampling system is designed.Recarding protocol security analysis,our protocol both considers collusion attacks and removes the security assumptions of the quantum channels.The theoretical simulation and calculation demonstrated that the proposed protocol is non-repudiable and transferable and eliminating the probability of forging attacks caused by employing the illegal strings.In the case of N participants,our protocol reduces the number of quantum links from CN2 in the previous signature protocol to N,which is beneficial for promoting the applications of quantum digital signature.A dynamic quantum multi-signature protocol based on Bell state entanglement correlation and module-two reflexivity is proposed,in which the participants are allowed to temporarily drop out or join in when the number of the participants is not beyond the threshold.When the number of the dropouts is over the preset threshold,the signature protocol can be appropriately cancelled.The signatory's dynamical behavior will not terminate the protocol,and there is no need to re-prepare entangled states or re-establish entangled relationships between multiple signers.This protocol solves the problem of inflexibility casued by the fixed entanglement relationship between multiple signers in the quantum multi-signature protocol.Five kinds of the round-pulse time delayers are innovatively proposed to effectively realize the adjustability and a wide value range of key parameter L of the round-robin differential phase shift quantum key distribution protocol.The round-pulse time delayers are used to build the variable-delay Mach-Zehnder interferometer,in which the delay range can be actively controlled by loading different phase codes.Jones matrix is used to prove the feasibility of the protosed delayers in theory.Moreover,these designs are experimentally verified by a practical optical system.By comparing the system key rate curves before and after using the delayer,it is further demonstrated that the proposed delayer also performs well in the round-robin differential phase shift quantum key distribution protocol.This round-pulse time delayer has the advantages of simple structure,stable performance,as well as easy to apply in high-speed systems.Compared with the previous experimental systems of the variable delay interferometers,this proposed scheme can realize low system error and avoid huge delay calibration.