The Research On Practical Security And Improvement Of Quantum Key Distribution

Taking quantum states as carriers,quantum key distribution(QKD)can provide the symmetric key distribution between two communication terminals,Alice and Bob.QKD’s security can be proved by the laws of quantum mechanics,thus has attracted widespread attention.Since BB84 protocol was proposed,many other QKD protocols have been proposed,such as measurement-device-independen-QKD(MDI-QKD)proto-col,sending-or-not-sending twin-field(SNS-TF)QKD protocol,and so on.The uncondi-tional security of these protocols have been rigorously proved,but their proofs are based on certain prerequisites.When the experimental conditions do not meet these prerequi-sites,security loopholes may occur and the key rate may be reduced.The research on the practical security and key rate improvement of QKD are the main contents of this paper.The decoy-state MDI-QKD protocol can ensure the security for QKD when using im-perfect single-photon sources and imperfect detection equipment.The 4-intensity MDI-QKD protocol is the mainstream of MDI-QKD protocols due to its highest key rate com-pared with other kinds of MDI-QKD protocols.Based on the 4-intensity MDI-QKD pro-tocol,we propose an improved method for calculating the key rate,which can further improve the key rate by more than 50%.In addition,we have studied the global optimiza-tion algorithm of the QKD protocol,and our results can reduce the optimization time as much as possible while ensuring the stability of the optimization results.The 4-intensity MDI-QKD protocol does not overcome all the problems faced in the practical MDI-QKD protocol.One of the most important problems is the security loophole caused by the intensity fluctuation.Based on the 4-intensity MDI-QKD proto-col,we study and obtain formulas of the secure key rate that include only the upper and lower bounds of the intensity fluctuation.The numerical results show that the 1% inten-sity fluctuation would reduce the key rate by half.In order to improve the performance of the protocol with intensity fluctuations,we then study a system where intensity fluctu-ations between different light sources are correlated.Numerical results show that the key rate in such a system is almost not reduced,compared with the system without intensity fluctuation,which greatly improves the practicability of our theory.SNS-TF QKD protocol can tolerate large misalignment errors,in which the relation-ship between the key rate and the channel transmission is ～ (?),and is one of the most practical TF QKD protocols.The security of SNS-TF QKD protocol with infi-nite key size has been proved.Here,we prove the security of SNS-TF QKD protocol with finite key size,according to the quantum information theories,and get the formula of the key rate by taking the finite-key effects into consideration.The numerical results show that the longest secure distance of SNS-TF QKD protocol can reach up to 600 km with finite key size.The odd-parity error correction(OPER)can further improve the key rate of SNS-TF QKD protocol.With the exponential quantum de Finetti theorem,we obtain the formula of the secure key rate of SNS-TF QKD protocol with OPER in the case of finite key size.Numerical results show that the OPER method can improve the key rate of SNS-TF QKD protocol by more than 100%,and the key rate of SNS-TF QKD protocol with OPER is the highest among all TF QKD protocols that consider the finite-key effects.