Optical Atomic Clock Comparison through Turbulent Air

TL;DR

This study demonstrates that optical two-way time-frequency transfer can accurately compare atomic clocks over open-air links despite atmospheric turbulence, achieving precision below 10^-18.

Contribution

It introduces a method for free-space optical clock comparison using frequency combs, achieving high precision despite turbulent air conditions.

Findings

Free-space optical clock comparison achieved 6×10^-19 accuracy.

Comparison over 1.5 km open-air link is feasible with turbulence.

Method supports sub-10^-18 precision in free-space conditions.

Abstract

We use frequency comb-based optical two-way time-frequency transfer (O-TWTFT) to measure the optical frequency ratio of state-of-the-art ytterbium and strontium optical atomic clocks separated by a 1.5 km open-air link. Our free-space measurement is compared to a simultaneous measurement acquired via a noise-cancelled fiber link. Despite non-stationary, ps-level time-of-flight variations in the free-space link, ratio measurements obtained from the two links, averaged over 30.5 hours across six days, agree to $6\times10^{-19}$, showing that O-TWTFT can support free-space atomic clock comparisons below the $10^{-18}$ level.