非球形气溶胶粒子及大气相对湿度对自由空间量子通信性能的影响∗

摘要

当量子光信号在自由空间中传输时,不可避免地会穿过大气,而存在于大气的气溶胶的光散射与吸收必然会影响量子光信号的传输.本文根据气溶胶粒子谱分布及其消光系数,提出了圆柱形、椭球形、Chebyshev三种非球形气溶胶粒子与链路衰减、量子纠缠度的关系；分析了大气相对湿度与量子纠缠度、保真度的定量关系.仿真结果表明,圆柱形、椭球形、Chebyshev三种非球形气溶胶粒子对链路的衰减程度依次递增；随着圆柱形、椭球形粒子的取向比和Chebyshev粒子的等效半径的增加,纠缠度呈不同的变化趋势；当大气相对湿度为0.2和0.9时,纠缠度和保真度分别为0.72,0.32和0.75,0.22.由此可见,非球形气溶胶粒子及大气相对湿度对量子通信系统的性能影响极大.所以,在实际的量子通信系统中,应根据不同非球形气溶胶粒子和大气相对湿度,自适应调整系统的各项参数,以提高量子通信的可靠性.%When the optical signal is transmitted in the free space, it inevitably passes through the atmosphere. The atmo-spheric aerosol is one of the most important components of the atmosphere, which not only affects the regional climate, but also influences the transmission of the free space optical signal. However, the study on the relationship between the non-spherical aerosols and the parameters of the free space quantum communication channel has not been carried out so far. To investigate this relationship, the spectral distribution function of the aerosol and its extinction factor should be analyzed first. According to three nonspherical aerosol particles: cylindrical particles, ellipsoidal particles and Chebyshev particles, the equation between channel attenuation of the free space quantum communication and the degree of quantum entanglement can then be established. After that, the effects of the relative humidity of the atmosphere on the degree of quantum entanglement and the fidelity of quantum communication can be analyzed and simulated finally. The simulation results show that the channel attenuations of the free space quantum communication are sequenced in ascending order as cylindrical particles, ellipsoidal particles, and Chebyshev particles, and their influences on the degree of quantum entanglement have different changing trends. When the transmission time is fixed, with the increase of aspect ratio of ellipsoidal particles, the degree of quantum entanglement shows a growing trend, with the increase of aspect ratio of cylindrical particles, the degree of quantum entanglement shows descending trend. With the increase of Chebyshev particle equivalent radius, the degree of quantum entanglement also shows the descending trend. When the relative humidity of the atmosphere is 0.2(0.9), the degree of quantum entanglement and the fidelity of quantum communication will be 0.72(0.75) and 0.32(0.22), respectively. It can be seen that the nonspherical aerosol particles and the relative humidity of the atmosphere each have a significant effect on the function of the free space quantum commu-nication system. Therefore, in a practical free space quantum communication system, the shape factor of nonspherical aerosol particle, orientating factor, equivalent radius and the relative humidity of the atmosphere cannot be ignored, in order to improve the effectiveness and reliability of the free space quantum communication, the different parameters of the communication system should be adjusted adaptively.