Absolute clock synchronization with a single time-correlated photon pair source over 10km

TL;DR

This paper presents a novel quantum-based protocol for absolute clock synchronization over 10 km fiber using a single photon pair source, enabling secure, distance-independent synchronization in a network.

Contribution

The authors introduce a new quantum synchronization method utilizing a single SPDC source and reflected photons, eliminating the need for multiple sources or complex optics.

Findings

Successful synchronization over 10 km fiber

Secure against symmetric delay attacks

Compatible with networked clocks

Abstract

We demonstrate a point-to-point clock synchronization protocol based on bidirectionally propagating photons generated in a single spontaneous parametric down-conversion (SPDC) source. Tight timing correlations between photon pairs are used to determine the single and round-trip times measured by two separate clocks, providing sufficient information for distance-independent absolute synchronization secure against symmetric delay attacks. We show that the coincidence signature useful for determining the round-trip time of a synchronization channel, established using a 10\,km telecommunications fiber, can be derived from photons reflected off the end face of the fiber without additional optics. Our technique allows the synchronization of multiple clocks with a single reference clock co-located with the source, without requiring additional pair sources, in a client-server configuration suitable for synchronizing a network of clocks.