Flaws in the process of modulation, or encoding of key bits in the quadratures of the electromagnetic light field, can make continuous-variable quantum key distribution systems susceptible to leakage of secret information. Here, we report such a modulation leakage vulnerability in a system that uses an optical in-phase and quadrature modulator to implement a single sideband encoding scheme. The leakage arises from the limited suppression of a quantum-information-carrying sideband during modulation. Based on the results from a proof-of-concept experiment, we theoretically analyze the impact of this vulnerability and show that the leakage reduces the range over which secret key can be obtained, and can even lead to a security breach, if disregarded. We also study the efficacy of additional trusted noise to counter this vulnerability.

调制过程中的缺陷，或电磁光场正交中关键位的编码，会使连续可变的量子密钥分发系统容易泄露秘密信息。在这里，我们报告了使用光学同相和正交调制器来实现单边带编码方案的系统中的这种调制泄漏漏洞。泄漏是由调制期间携带量子信息的边带的有限抑制引起的。基于概念验证实验的结果，我们从理论上分析了此漏洞的影响，并表明泄漏会缩小可以获得密钥的范围，如果不理会，甚至可能导致安全漏洞。我们还研究了额外可信噪声对抗此漏洞的功效。