Continuous-variable quantum key distribution with coherent detection is widely acknowledged for its compatibility with contemporary optical communication technologies. However, the robustness of various modulation formats and detection procedures against high excess noise remains uncertain, posing a significant barrier to the widespread implementation of quantum key distribution networks. This paper introduces a Matlab and Simulink-based experimental simulator designed to analyze different modulation formats (Gaussian and discrete) and coherent detection techniques (homodyne, heterodyne, and intradyne). Our findings suggest that polarization-multiplexed quantum signals with discrete modulation and pilot tones exhibit greater resilience to experimental imperfections. Enhanced robustness can be achieved through post-selection. Furthermore, under conditions of trusted detector noise, intradyne detection proves more effective in mitigating various offsets between the two nodes, thereby resulting in an increased secret key rate. The secure key rate is determined using the Gaussian extremity theorem for Gaussian modulation and a strict numerical technique against collective attacks in the asymptotic regime for discrete modulation. The results demonstrate that the protocol enables key distribution over distances approaching intercity scales, thereby supporting the advancement of cost-effective quantum-secure communication networks.
Gupta et al. (Thu,) studied this question.