Security analysis of discretized polar modulation continuous-variable quantum key distribution.

Abstract

In experimental setups of Gaussian modulation continuous-variable quantum key distribution (CV-QKD), the amplitude and phase of coherent states will be modulated and discretized due to the finite resolution of voltages that drive electro-optical modulators, resulting in Gaussian modulation discretization. We demonstrate that the impact of discretization on CV-QKD can be described as a multiplicative coefficient experimentally and modeled as a preparation noise imposed on ideal Gaussian modulation theoretically. To obtain an accurate estimation of quadrature fluctuation induced by discretized polar modulation, a data-filtering process named preselection can be applied before state transmission. Numerical results show that when amplitude resolution is 0.25 and phase resolution is 0.02, discretized polar modulation enables a transmission distance of 69 km under homodyne detection, reaching 89% of ideal Gaussian modulation. As for heterodyne detection, 55 km and 80% are achieved.