To achieve the maximum information transfer and face a possible eavesdropper, the samples transmitted in continuous-variable quantum key distribution (CV-QKD) protocols are to be drawn from a continuous Gaussian distribution. As a matter of fact, in practical implementations the transmitter has a finite (power) dynamics and the Gaussian sampling can be only approximated. This requires the quantum protocols to operate at small powers. In this paper, we show that a suitable probabilistic amplitude shaping of a finite set of symbols allows to approximate at will the optimal channel capacity also for increasing average powers. We investigate the feasibility of this approach in the framework of CV-QKD, propose a protocol employing discrete quadrature amplitude modulation assisted with probabilistic amplitude shaping, and we perform the key generation rate analysis assuming a wiretap channel and lossless homodyne detection.

翻译：为实现最大信息传输并应对潜在窃听者，连续变量量子密钥分发（CV-QKD）协议中传输的样本需从连续高斯分布中抽取。然而在实际实现中，发射机存在有限的功率动态范围，高斯采样仅能近似实现，这要求量子协议在低功率下运行。本文证明，通过对有限符号集进行适当的概率幅值整形，可在平均功率增大时任意逼近最优信道容量。我们研究了该方案在CV-QKD框架中的可行性，提出了一种采用离散正交幅度调制并辅以概率幅值整形的协议，并在窃听信道和无损零差检测条件下完成了密钥生成速率分析。