Demonstration of quantum synchronization based on second-order quantum coherence of entangled photons

TL;DR

This paper demonstrates a quantum clock synchronization method using second-order quantum coherence of entangled photons, achieving high timing stability over a 4 km fiber link, with potential for femtosecond accuracy.

Contribution

It presents a proof-of-principle experiment for quantum clock synchronization utilizing second-order quantum interference, advancing high-precision timing technology.

Findings

Achieved 0.4 ps timing stability over 16000 s

Absolute time accuracy of 59.4 ps

Potential for better than 10 fs accuracy

Abstract

Based on the second-order quantum interference between frequency entangled photons that are generated by parametric down conversion, a quantum strategic algorithm for synchronizing two spatially separated clocks has been recently presented. In the reference frame of a Hong-Ou-Mandel (HOM) interferometer, photon correlations are used to define simultaneous events. Once the HOM interferometer is balanced by use of an adjustable optical delay in one arm, arrival times of simultaneously generated photons are recorded by each clock. The clock offset is determined by correlation measurement of the recorded arrival times. Utilizing this algorithm, we demonstrate a proof-of-principle experiment for synchronizing two clocks separated by 4km fiber link. A minimum timing stability of 0.4 ps at averaging time of 16000 s is achieved with an absolute time accuracy of 59.4 ps. The timing stability is verified to be limited by the correlation measurement device and ideally can be better than 10 fs. Such results shine a light to the application of quantum clock synchronization in the real high-accuracy timing system.