Two-stage Phase Compensation for Continuous-Variable Quantum Key Distribution

The traditional phase compensation method in CVQKD (continuous variable quantum key distribution) usually assumes that the phase drift within a frame is constant. However, in reality, there are usually small phase drifts within a frame, especially in free space. Unperfect compensation of phase drifts can introduce additional phase noise, which can reduce key rate and transmission distance. To address this issue, we propose a two-stage phase compensation scheme that inserts different length phase drift compensation blocks to not only compensate for the average phase drift of a frame but also to compensate for the internal phase drift fluctuations within the frame. This enables more accurate phase drift compensation, particularly useful for scenarios with large and fast phase drift fluctuations.