An optical quantum communication system with receiver diversity is proposed for free-space communication using the optical combining technique and a generalized Kennedy receiver. The quantum channel model of the proposed system is established using the $P$ -representation in the presence of both turbulence and thermal noise. A conditional dynamics based Kennedy receiver with threshold detection is proposed to mitigate the influence of both turbulence and thermal noise. The error probabilities for different types of generalized Kennedy receiver, i.e., the Kennedy receiver, the Type-II receiver, and the conditional dynamics based Kennedy receiver, are analytically studied and the lower bounds for these error probabilities are obtained. Numerical results show that both the Kennedy receiver and the Type-II receiver fail in the presence of either turbulence or thermal noise. The performance of the proposed conditional dynamics based Kennedy receiver with threshold detection can surpass the standard quantum limit given by the homodyne receiver in either weak turbulence or small thermal noise.

中文翻译：

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具有接收机分集的湍流信道中的自由空间光量子通信

提出了一种具有接收器分集的光量子通信系统，用于使用光组合技术和广义肯尼迪接收器的自由空间通信。在存在湍流和热噪声的情况下，所提出系统的量子通道模型是使用 $P$ 表示建立的。提出了一种具有阈值检测的基于条件动力学的肯尼迪接收器，以减轻湍流和热噪声的影响。分析研究了不同类型的广义肯尼迪接收器，即肯尼迪接收器、II 型接收器和基于条件动力学的肯尼迪接收器的误差概率，并获得了这些误差概率的下界。数值结果表明，Kennedy 接收器和 Type-II 接收器在存在湍流或热噪声的情况下都会失效。提出的具有阈值检测的基于条件动力学的肯尼迪接收器的性能可以超过零差接收器在弱湍流或小热噪声下给出的标准量子限制。