Fast qubit-based frequency-recovery algorithm for quantum key distribution
Phys. Rev. Applied 24, 064071 – Published 29 December, 2025
DOI: https://doi.org/10.1103/mbc7-fzk3
Abstract
Clock synchronization serves as a foundational subsystem in quantum key distribution (QKD). The recently proposed qubit-based synchronization (Qubit4Sync) presents opportunities in eliminating additional cost, noise, and potential side channels. It offers a promising alternative to dedicated synchronization hardware. However, the current frequency-recovery process in Qubit4Sync requires high data throughput and computational speed, limiting practical use. To overcome these issues, we have developed a fast frequency-recovery algorithm that increases the recovery rate by several orders of magnitude and remains robust under a bad signal-to-noise ratio (SNR). This enables Qubit4Sync to operate effectively in mainstream gated-mode QKD systems. We further establish a theoretical model for frequency recovery, showing that our algorithm is robust against disturbances such as dead time, jitter, and afterpulse. A frequency-domain SNR calculation method is also provided to guide parameter design for specific experimental conditions. This work opens the door to practical Qubit4Sync deployment in general QKD systems.
