Investigating the impact of clock frequency stability on practical quantum key distribution

Qubit-based synchronization offers an approach for quantum key distribution (QKD), simplifying system architecture and reducing implementation costs by leveraging the exchanged qubits. However, the performance of such schemes hinges on accumulating sufficient qubit events, making them sensitive to local clock frequency instability, especially under high channel loss. This study investigates the impact of frequency instability in non-ideal oscillators, emphasizing clock drift-induced deterioration on QKD performance in these challenging, lossy conditions. We simulate the performance of actual QKD key generation rates under optimal acquisition times for different levels of channel loss. Experimental validation, using QKD systems with two distinct clock configurations, confirms secure key generation and reliable operation up to 67 dB channel loss. We propose this model as a general tool for evaluating and optimizing the synchronization subsystems within the broader quantum communication infrastructure.