Balancing four-state continuous-variable quantum key distribution with linear optics cloning machine

Wu Xiao-Dong¹, Liao Qin¹, Huang Duan^{1, 2, †}, Wu Xiang-Hua¹, Guo Ying^{1, 3, ‡}

(color online) Comparison of the correlation for two different modulation protocols. Full lines correspond to the four-state protocol (correlation marked as Z₄) and dashed lines correspond to the Gaussian modulation protocol (correlation marked as Z_G). Both Z₄ and Z_G are functions of the modulation variance . (a) V_A in a large range, and (b) V_A in a small range.