Pre-calibration and compensation of quadrature components in continuous-variable quantum key distribution

Quantum key distribution (QKD) can guarantee the security of key distribution through the basic principles of quantum mechanics. The theoretical security proof framework of continuous-variable QKD (CV-QKD) using two quadrature components to carry encryption key information has also been gradually completed. However, there are still deviations between theoretical assumption and experimental implementation that caused by the imperfection of the practical devices. Aiming at the responsivity of the detection imbalance and angular deviation of the dual homodyne detectors, we propose a pre-calibration and compensation scheme to eliminate the deviation of quadrature components. Specifically, the cross-correlation between the transmitted and received data is calculated, which is used to derive the transmission matrix. According to this transmission matrix, the data can be compensated during the actual CV-QKD. We simulate our scheme under different detector noises, responsivity imbalance, and angular deviation of the dual homodyne detectors. The results show that the scheme can accurately compensate the data, keep the excess noise below the security threshold, and generate the secure key even using imperfect devices. At the same time, the experiment also shows that this scheme can recover the quantum signal well and reduce the excess noise effectively. Considering that this scheme can solve the imperfect but common device problems, it makes a crucial step toward the new generation of practical CV-QKD systems based on signal processing.