The practical implementation difficulties arising from the Gaussian modulation of the GG02 protocol lead us to investigate the possibilities offered by the combination of probabilistic amplitude shaping technique and quadrature amplitude modulation formats in the context of continuous variable quantum key distribution systems. Our interest comes from the fact that quadrature amplitude modulation and probabilistic shaping can be implemented with current technologies and are widely used in classical telecom equipment. In this treatment, we assume to work in the scenario of a linear quantum channel and we analyze maximum achievable secure key rates, maximum reachable distances and the resilience to noise of our discrete-modulation based protocol with respect to GG02, which is taken as a benchmark. In particular, we deal with the infinite key size regime, consider a homodyne detection scheme, and analyze what happens for different cardinalities of the input alphabet at different distances, in the case of collective attacks and in the reverse reconciliation picture. We find that our protocol, beyond being easily reproducible in the laboratory, provides a way to closely approach the theoretical performance offered by GG02 and, at the same time, preserves the ability to assure an unconditional security level.

翻译：GG02协议中高斯调制带来的实际实现困难促使我们研究在连续变量量子密钥分发系统中结合概率幅度整形技术与正交幅度调制格式的可能性。我们的研究兴趣源于正交幅度调制和概率整形均可利用现有技术实现，且已广泛应用于经典电信设备。在本研究中，我们假设工作在线性量子信道场景中，并以GG02协议为基准，分析了基于离散调制的协议在最大可实现安全密钥率、最大可达传输距离及抗噪性能方面的表现。具体而言，我们在无限密钥长度体系下，采用零差检测方案，分析了集体攻击场景和反向协调框架中，不同输入字母表基数在不同传输距离下的性能表现。研究发现，我们的协议不仅易于在实验室复现，还能以接近GG02协议理论性能的方式运行，同时保持确保无条件安全水平的能力。