Subject of study. This study considers a polarization control method of optical radiation for a continuous-variable quantum key distribution system for correct polarization demultiplexing of the local oscillator and signal state necessary to ensure the correct performance of the presented system. Aim of study. This study aims to develop a system of active polarization control and experimentally evaluate the effect of this system on the continuous-variable quantum key distribution system parameters. Method. The polarization control system considered in this study is based on constant analysis of the local oscillator radiation and maximization of its intensity due to the stochastic gradient descent algorithm. Local oscillator fluctuations occur because of the principle of active polarization control operation. An experimental setup simulating the sender and receiver module of the continuous-variable quantum key distribution system is used to evaluate the introduced noise. This setup enables evaluation of the noise introduced by the controller operation. Main results. Excess noise caused by the polarization controller is comparable with the polarization noise generated in the quantum key distribution system. Practical significance. Correct operation of a continuous-variables quantum key distribution system can be implemented exclusively with the use of a polarization control device. Knowledge of the polarization control effect on the system gains an understanding of the possible future methods for designing and developing continuous-variables quantum key distribution systems.
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