Classical clock synchronization for quantum communications using the quantum channel

We present a time synchronization method for correlation of photon arrival times for quantum communication. The method employs a low-power, low-frequency synchronization beacon that shares the quantum channel and is detected using the same single-photon detectors already present in the quantum communication system. We show experimentally that the system jitter approaches the system resolution limit with negligible impact on the quantum channel in realistic use cases. The presented method is particularly suitable for long distance quantum communication with large clock drifts, such as quantum links involving satellites.