Dynamic rerouting and interruption resilience of quantum communication via single-photon-based resynchronization

We present a resynchronization method for quantum key distribution (QKD) systems that enables rapid and reliable recovery from interruptions of the quantum channel and changes of its optical path length. By periodically transmitting short fixed pulse patterns over the quantum channel, our approach achieves swift clock offset recovery, typically within a few hundred milliseconds. We implemented this method in our time-bin-phase BB84 QKD system, demonstrating successful resynchronization after multi-minute channel interruptions and fiber length changes exceeding 100 km. The method can be retrofitted to existing systems via a software upgrade and without hardware changes, allowing for broad applicability. In total, the resynchronization method significantly enhances QKD system resilience and allows for reliable operation in challenging environments such as dynamically routed optical networks, i.e., software-defined networks, and free-space optical links with mobile nodes.