Ultra-stable Free-Space Laser Links for a Global Network of Optical Atomic Clocks

TL;DR

This paper demonstrates ultra-stable free-space laser links over 2.4 km atmospheric paths, enabling precise clock comparisons crucial for a global optical atomic clock network and advancing related technologies.

Contribution

It presents the first demonstration of high-stability laser frequency transfer over a turbulent atmospheric link suitable for ground-to-space clock comparisons.

Findings

Achieved fractional frequency stability of 6.1E-21 in 300 s

Clock comparison limited by clock stability after a few seconds

Advances in free-space laser link technology for global clock networks

Abstract

A global network of optical atomic clocks will enable unprecedented measurement precision in fields including tests of fundamental physics, dark matter searches, geodesy, and navigation. Free-space laser links through the turbulent atmosphere are needed to fully exploit this global network, by enabling comparisons to airborne and spaceborne clocks. We demonstrate frequency transfer over a 2.4 km atmospheric link with turbulence similar to that of a ground-to-space link, achieving a fractional frequency stability of 6.1E-21 in 300 s of integration time. We also show that clock comparison between ground and low Earth orbit will be limited by the stability of the clocks themselves after only a few seconds of integration. This significantly advances the technologies needed to realize a global timescale network of optical atomic clocks.