Chenkai Li

The remote clock synchronization in the Quantum Key Distribution (QKD) system usually relies on the transmission of synchronous optical pulses. However, the real-time jitter in the free-space channel can lead to the loss of synchronous optical pulses and the drift of the time reference. Moreover, the non-uniform distribution of channel loss in the existing post-processing methods will reduce the encoding efficiency of the filtered keys. The traditional solutions monitor the link attenuation information through independent synchronous optical signals and actively discard the key data during high-loss periods. However, this solution requires additional hardware support and has synchronization constraints. This study proposes a synchronization scheme based on real-time automatic threshold selection. By analyzing the time drift characteristics of the synchronous detector under different link attenuation conditions, this method directly realizes the automatic screening of high-loss data. This method eliminates the dependence on real-time monitoring of synchronous optical signals and achieves the automation of threshold setting through hardware architecture optimization. This solution can improve the encoding efficiency of the free-space QKD system and its principle is applicable to synchronous systems based on protocols such as BB84. This research provides a new technical path for the design of synchronization schemes for free-space quantum communication systems.