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

The two-way quantum clock synchronization has been shown to provide femtosecond-level synchronization capability and security against symmetric delay attacks, thus becoming a prospective method to compare and synchronize distant clocks with enhanced precision and safety. 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 is implemented by using time-energy entangled photon-pair sources. Limited by the intrinsic frequency stability of the Rb clock, the achieved time stability at 30 s is measured as 32 ps. By applying a fiber-optic microwave frequency transfer technology to build frequency syntonization between the separated clocks, the limit set by the intrinsic frequency stability of the Rb clock is overcome. A significantly improved time stability of 1.9 ps at 30 s is achieved, which is mainly restrained by the low number of acquired photon pairs due to the low sampling rate of the utilized coincidence measurement system. Such implementation demonstrates the high practicability of the two-way quantum clock synchronization method for promoting field applications. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

Two-way quantum clock synchronization provides femtosecond-level synchronization capability and protection against symmetric delay attacks, making it a promising method for comparing and synchronizing distant clocks. This letter presents a field test of two-way quantum synchronization between an H-maser and an Rb clock connected by a 7 km fiber. The achieved time stability is limited by the intrinsic frequency stability of the Rb clock, but can be improved by applying a fiber-optic microwave frequency transfer technology.