Optimized Qubit-Based Synchronization in Quantum Key Distribution

Quantum key distribution (QKD) enables the generation of information-theoretic secure keys between two remote parties. A critical component of successful QKD implementation is the effective synchronization of clocks between these users. Traditional methods of locking to a reference clock or transmitting a synchronization signal rely on auxiliary equipment, which increases the complexity and cost, thus hindering the widespread deployment of QKD. Here, we propose a method to achieve clock and pulse synchronization by exploiting a subset of the transmitted qubits. We demonstrate our scheme with a time-bin phase-coding BB84 QKD system and verify the realization of long-term stable key generation over distances of 50 km and 100 km. Our method simplifies the implementation of QKD systems and introduces new possibilities for synchronization algorithms in other quantum communication protocols.