Research On Continuous Variable Quantum Communication Based On Gaussian Modulation

Quantum communication theory is one of the core.contents of quantum information science.It has opened up a new way for the security of the information transmission and brought new vitality for cryptography and communications science.Since the BB84 protocol has been put forward,theory and experiment have made numerous important research achievements whether discrete or continuous variable quantum communication.Meantime,these achievements show that quantum communication has great application prospect and commercial value,which attract many governments around the world to invest amounts of human and financial resources for further research.Compared to the earlier discrete variable quantum cryptography,the continuous variable quantum cryptography has great advantages,such as the signal source used coherent light,low cost,easy integration.In this paper,we describe the Gaussian-modulated continuous variable quantum communication process and study secret key rate in detail,also security of the communication scheme is analyzed and discussed deeply.The main research contents are as follows:(1)Compared to the general communication scheme,the scheme of continuous variable quantum communication with symmetric configuration has certain advantages.We can increase the mutual information between Alice and Bob based measurement device independent.Utilizing the theory of measurement and quantum information,we acquire theoretical secret key rate based on entangled representation.At the same time,we study the derivation of the conditional covariance matrices obtained by both sides of communication and eavesdroppers.The theoretical expression of the continuous variable quantum secret key rate is calculated by using the relationship between the symplectic eigenvalue of the matrix and the Von Neumann entropy.(2)We performed a security analysis of the continuous variable quantum communication system with symmetric configuration.According to the relationship between the correlation parameters and the physical environment,we classify the attack types and get the best attack method by numerical simulation,and acquire the secret key rate against the best attack method.Then,the security secret key rate is deeply analyzed.We take the detection efficiency of the detectors into account which is simulated by two beam splitters.Finally,under the condition of symmetrical configuration,we obtain secret key rate against the two-mode quantum Gaussian attacks with the condition that the quantum efficiency of detectors is not 1.