Influence Of Imperfect Faraday Mirror On The Practical Security Of Continuous Variable Quantum Key Distribution System

Quantum key distribution is a quantum technology that develops faster and has a higher degree of practicality in quantum information,and theoretically has unconditional security.The security of quantum cryptosystem also depends on the accuracy of related system devices,but under the pratical circumstance,the devices used in system are not always perfect,and the existing errors will cause the practical system and the theoretical model to not be perfectly matched,which may bring loopholes for system and the practical security of the system cannot be guaranteed.This paper studies the influence of imperfect Faraday Mirror on two different continuous variable quantum key distribution systems.The main contents are as follows:1.The influence of imperfect Faraday Mirror on continuous variable quantum key distribution system with Gaussian modulation coherent state protocol is studied.The research results show that the imperfection of the Faraday Mirror will reduce the performance of the system.As the degree of imperfection of the device increases,the practical security key rate of the system exhibits a cosine periodic variation rule.A compensation scheme is proposed,in which the legal party can judge the condition of the Faraday Mirror,if the device is not perfect,the lost performance of the system can be compensated.In addition,the feasibility analysis of this scheme is carried out and compared with another scheme.2.The influence of imperfect Faraday Mirror on continuous variable quantum key distribution system with Plug-and-play dual-phase-modulated is studied.The research results show that the imperfection of the Faraday Mirror will impair the performance of the system,declining practical secret key rate of the system and shortening the secure communication distance.And the secret key rate also presents a cosine periodic variation with the increase of the imperfection of the device.An attack based on the imperfection of the Faraday Mirror is proposed,and the excess noise of the system and the secret key rate that the eavesdropper can steal are calculated under this attack behavior.