The Effects Of Space Channel Characteristics On The Performance Of Quantum Communication Systems

Compared with the optical fiber channel,space channel has the advantages of strong flexibility,low transmission loss and long transmission distance,which has became an indispensable part to construct quantum communication system between satellite and ground.However,the quantum signal transmitted through the space channel will inevitably be affected by atmospheric effects,which will cause the decrease of secret-key rate or the reduction of communication distance.Therefore,this paper investigates how characteristics of space channel affect the performance of quantum communication system.The main research contents are as follows.Firstly,an entanglement-based Gaussian modulation continuous variable key distribution model based on space channel is established.Based on model,the calculation formulas of secret-key rate under different types of attack and detection are given.An expression is proposed to calculate the interruption probability based on the Kolmogorov spectrum model.Then,the effects of atmospheric attenuation and turbulence on the transmittance,extra noise and interruption probability for different wavelengths signals are investigated.Secondly,This paper analyzes how characteristics of space channel affect the secret-key rate of the CVQKD system.Various conditions such as three signal wavelengths(810nm,1550 nm,3800nm),two weather conditions,two detection schemes,and two types of attack are considered in our investigation.The results show that 3800 nm signal can transmit much further than 1550 nm and 810 nm in both clear weather and fog.Moreover,a system employing homodyne detection can achieve longer distance than that of using heterodyne detection in both collective attack and individual attack.Finally,in order to improve the performance of free space quantum communication system,phase sensitive amplifier and phase insensitive amplifier are used to compensate the performance degradation caused by the unideality of the detector.The formulas to calculate secret-key rate with using the above two kinds of amplifiers are derived.Considering Bob using homodyne and heterodyne detections,and the free space quantum communication system is suffering individual and collective attacks,respactively,the relationship between secret-key rates of three wavelengths signals and transmission distance is simulated.The promotion effect of using phase sensitive amplifier and phase insensitive amplifier on the performance of quantum communication system is studied.A suggestion for the actual free space quantum communication system of how to select the optical amplifiers is given.Furthermore,the influence of the inherent noise of the phase insensitive amplifier on the secret-key rate is analyzed.