Implementation of field two-way quantum synchronization of distant clocks across a 7 km deployed fiber link

TL;DR

This paper demonstrates a practical implementation of two-way quantum clock synchronization over a 7 km fiber link, achieving femtosecond-level stability and enhanced security, with improved stability using microwave frequency transfer technology.

Contribution

It presents the first field test of two-way quantum synchronization over deployed fiber, combining quantum and microwave techniques for improved stability and practicality.

Findings

Time stability of 32 ps at 30 s with Rb clock

Improved stability to 1.9 ps using microwave frequency transfer

Feasibility of quantum synchronization in real-world field conditions

Abstract

The two-way quantum clock synchronization has been shown not only providing femtosecond-level synchronization capability but also security against symmetric delay attacks, thus becoming a prospective method to compare and synchronize distant clocks with both enhanced precision and security. In this letter, a field test of two-way quantum synchronization between a H-maser and a Rb clock linked by a 7 km-long deployed fiber was implemented. Limited by the frequency stability of the Rb clock, the achieved time stability at 30 s was measured as 32 ps. By applying a fiber-optic microwave frequency transfer technology, the stability was improved by more than one-magnitude to 1.9 ps, even though the number of acquired photon pairs was only 1440 in 30 s due to the low sampling rate of the utilized coincidence measurement system. Such implementation demonstrates the high practicability of two-way quantum clock synchronization method for promoting the field applications.