Guarding security of quantum key distribution using blind calibration

Quantum key distribution (QKD) has emerged as a leading quantum technology for secure key exchange, achieving notable advancements in both theoretical and experimental domains. Despite these successes, practical QKD systems remain vulnerable to security risks due to device calibration. In this study, we propose a revised blind calibration scheme that incorporates mixed states with concealed information, safeguarding the calibration process from eavesdropping, thereby enhancing the security of the detector calibration and reference frame calibration processes. Furthermore, we introduce a gradient algorithm to dynamically adjust the activation time of the gated single-photon detectors, maintaining the maximum detection efficiency while monitoring whether the calibration process is subjected to quantum man-in-the-middle attack. Experimental results demonstrate that our approach reduces the quantum bit error rate from 50% to 1.5% over transmission distances of 50, 100, and 150 km. This enhanced calibration method improves the practical security of QKD and supports the large-scale deployment of QKD systems.