Research On The Security Of A Probability-based Phase-modulated Continuous Variable Quantum Key Distribution System

Quantum key distribution based on quantum mechanics is theoretically unconditionally secure in theory.At present,quantum key distribution mainly includes two technical means: discrete variables and continuous variables.The popularity of discrete variable quantum key distribution is limited by the greater difficulty of singlephoton detection and preparation.Since continuous variable quantum key distribution can be integrated with the current optical fiber communication network infrastructure,it has unique advantages in actual use scenarios.This dissertation is mainly based on the continuous variable quantum key distribution in the form of discrete modulation.The main research content has the following two aspects:1.Based on the security analysis framework of the discrete modulation protocol,a three-state continuous variable quantum key distribution protocol based on postselection and discrete modulation is proposed.And in the case of reverse coordination and collective attack,the security code rate formula of the three-state discrete modulation protocol is derived.Numerical simulation analysis results show that when the transmission distance is short,the three-state discrete modulation can achieve a higher security code rate than the four-state discrete modulation,which shows that the three-state discrete modulation is more suitable for small-scale key distribution such as metropolitan area networks scenes.2.Based on the coherent state and the post-selected discrete modulation protocol,the circular modulation scheme and the square modulation scheme are proposed according to the different modulation methods,and the general security code rate formula of the protocol is deduced in the case of reverse coordination and collective attack.Numerical simulation analysis results show that under different signal states,the performance of the square discrete modulation protocol is generally better than that of the circular discrete modulation protocol.Compared with other protocols,the performance of the four-state square discrete modulation protocol is the best.