Quantum two-way time transfer over a hybrid free-space and fiber link

TL;DR

This paper demonstrates the first experimental quantum two-way time transfer over a hybrid free-space and fiber link, achieving sub-picosecond stability despite turbulence and loss, advancing quantum-enhanced remote time synchronization.

Contribution

It presents the first experimental implementation of quantum two-way time transfer over a hybrid free-space and fiber link, showing feasibility for space-ground optical synchronization.

Findings

Achieved reliable time transfer with stability below 1 ps over 2 km free space and 7 km fiber.

Demonstrated robustness against atmospheric turbulence and high loss.

Validated quantum time transfer for space microwave atomic clock synchronization.

Abstract

As the superiority of quantum two-way time transfer (Q-TWTT) has been proved convincingly over fiber links, its implementation on free-space links becomes an urgent need for remote time transfer expanding to the transcontinental distance. In this paper, the first Q-TWTT experimental demonstration over a hybrid link of 2 km-long turbulent free space and 7 km-long field fiber is reported. Despite the significant loss of more than 25 dB and atmospheric turbulence, reliable time transfer performance lasting for overnights has been realized with time stability in terms of time deviation far below 1 picosecond. This achievement shows the good feasibility of quantum-enhanced time transfer in the space-ground integrated optical links and nicely certifies the capability of Q-TWTT in comparing and synchronizing the state-of-the-art space microwave atomic clocks.