单光子斜程量子信道纠缠角动量的大气湍流效应

The effects of atmospheric turbulence on entangled orbital angular momentum of single photons for slant quantum communication

分析了von Karman型湍流大气对量子光信道中传输的由参量下转换源生成纠缠轨道角动量态的影响。运用Rytov近似、波相位结构函数的平方近似和修正von Karman折射率起伏谱,研究了完整包含大气湍流引入振幅与位相起伏效应的斜程湍流大气通信信道中单光子纠缠轨道角动量态的测量概率模型,建立了长曝光与短曝光两种曝光条件下斜程湍流大气传输单光子纠缠轨道角动量态的测量概率理论关系。数值研究了天顶角分别为θ=π/6和θ=π/3时的长短或曝光情况下,轨道角动量态纠缠光子对联合概率随着传输距离的变化。数值结果表明:在z<500m的传输距离内,纠缠光子对的联合检测概率随传输距离增加而快速下降,但传输距离达z>1000m后联合检测概率几乎不再下降;结果也发现,携带轨道角动量小的纠缠光子对的联合测量概率减少率比携带轨道角动量大的纠缠光子对的联合测量概率的要小;光束传输天顶角越大,联合概率下降幅度越大。

The offects of the atumospheric turbutence on z-tilt corrected or beam center tracked entangled orbital angular momentum（OAM）states generated by parametric down conversion and propagation in atmospheric communication channel are studied,and the entangled orbital angular momentum states detection probabilities of signal photon which are propagation in slant atmospheric turbulence and include the z-tilt corrected or beam center tracked phase fluctuation and amplitude fluctuation caused by atmospheric turbulence are modelled.The joint detection probabilities of OAM state entangled photons versus propagationdistance for the zenith angle θ=π/6 and θ=π/3 are calculated numerically.The results demonstrate that when propagation distance z〈 500m,the joint detection probability of entangled photons decays rapidly as propagation distance increases,but when propagation distance z〉1000m,the decay-rate of the joint detection probability of entangled photons is vary small as propagation distance increases.It is shown that the joint detection probabilities of entangled photons with lower total OAM decay less rapidly than those with higher OAM values.It is also found that the joint detection probabilities of entangled photons with smaller zenith angle decay less rapidly than those with larger zenith angle.