近日，俄罗斯科学院斯特克洛夫数学研究所的Andrei Gaidash及其研究团队取得一项新进展。经过不懈努力，他们揭示连续变量量子密钥分发可观测值的模间相互作用诱导的动力学。相关研究成果已于2024年6月21日在国际知名学术期刊《物理评论A》上发表。

该研究团队从理论上研究了，控制连续变量(CV)量子密钥分发(QKD)系统运行条件的可观测值的动力学机制，这些可观测值紧密依赖于量子信道引起的模间相互作用。与常见的通过分束器变换引入损耗和热展宽的方法不同，该研究采用了精确可求解的量子通道模型，来详细描述与热浴相互作用的多模玻色子系统的林德布莱德动力学，并充分考量了同差探测方案中的潜在缺陷。

研究人员基于光子计数差和正交概率分布的解析结果，推导出了合法通信方之间互信息的表达式，这一表达式直接关联了CV QKD的信息特性与信道参数。特别地，针对在光纤通道中传输的双模光子系统这一重要场景，研究人员使用了频率和弛豫速率矢量，来表征玻色子模式间的相干（动态）模间耦合与非相干（环境介导）相互作用，使得参数化过程更加便捷。

研究结果显示，这些矢量对于互信息以及信号与本地振荡器之间相位差的动力学机制具有决定性作用，并揭示了四种定性不同的动力学机制，这些机制可能会显著影响CV QKD系统的运行。

附：英文原文

Title: Intermode-interaction-induced dynamics of continuous-variable quantum-key-distribution observables

Author: Andrei Gaidash, Alexei D. Kiselev, George Miroshnichenko, Anton Kozubov

Issue&Volume: 2024/06/21

Abstract: We theoretically study the dynamical regimes of the observables that govern the operating conditions of continuous-variable (CV) quantum-key-distribution (QKD) systems, depending on quantum-channel-induced intermode interactions. In contrast to the widely used approach in which losses and thermal broadening are introduced through a beam-splitter transformation, our analysis uses the exactly solvable quantum channel model describing the Lindblad dynamics of multimode bosonic systems interacting with a heat bath and additionally takes into account imperfections of the homodyne-detection scheme. The analytical results for the photon-count difference and the quadrature probability distributions are used to derive the expression for the mutual information between legitimate parties, which explicitly links the information properties of CV QKD and the parameters of the channel. For the important special case of a two-mode photonic system propagating in a fiber channel, the latter can be conveniently parameterized using the frequency and the relaxation-rate vectors that characterize the coherent (dynamical) intermode couplings and the incoherent (environment mediated) interaction between the bosonic modes, respectively. It turns out that these vectors determine four qualitatively different dynamical regimes of the mutual information and the phase difference between the signal and the local oscillator that may significantly affect the operation of CV QKD.

DOI: 10.1103/PhysRevA.109.062615

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.109.062615