Adaptive-sign CMA for continuous-variable quantum key distribution under high-speed polarization disturbances

Polarization disturbance in long distance single-mode fiber is detrimental to both the classical and quantum communications. Here we proposes an adaptive-sign constant modulus algorithm (AS-CMA) using an error-driven adaptive step size and a sign-based weight update, which jointly enhances the performance while reducing the computational complexity of the conventional CMA. We validate the algorithm on a continuous-variable quantum key distribution system. Simulation results show that under 10 Mrad/s polarization disturbance, the secret key rate achieved using AS-CMA method only decreases by 12.9% at 25 km single-mode fiber. Robust polarization recovery and positive secret key rate can be maintained even under extreme 43 Mrad/s lightning transients. Our results provides an efficient, low-complexity solution for polarization recovery in CV-QKD system.