Optical atomic clock comparison through turbulent air

Martha I Bodine,William R Milner,Scott A Diddams,William F Mcgrew,Xiaogang Zhang,David R Leibrandt,Tobias Bothwell,Holly Leopardi,Andrew D Ludlow,Lindsay Sonderhouse,William C Swann,Dhruv Kedar,Jun Ye,Youssef S Hassan,Isaac H Khader,Jeffrey A Sherman,Jian Yao,Sarah L Bromley,Tara M Fortier,Jean-Daniel Deschênes,Nathan R Newbury,Colin J Kennedy,Laura C Sinclair,Daniele Nicolodi,Jwo-Sy Chen,Stefania Romish,Samuel M Brewer,K Beloy ,Robert Fasano ,A Sophia Koepke ,John Robinson ,Stefan Alaric Schäffer ,E Oelker ,T.e Parker ,David Hume

doi:10.1103/physrevresearch.2.033395

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 nonstationary, 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 6×10−19, showing that O-TWTFT can support free-space atomic clock comparisons below the 10−18 level.Received 1 June 2020Accepted 4 August 2020DOI:https://doi.org/10.1103/PhysRevResearch.2.033395Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAtomic, optical & lattice clocksOptics & lasersAtomic, Molecular & Optical

Highlights

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 two optical clocks consisted of frequency combs phase-locked to cavity-stabilized lasers, which served as optical reference oscillators
We find that the frequency ratios measured by the free-space and fiber links agree to an uncertainty of 6 × 10−19, and the instability of Published by the American Physical Society the loopback test reaches 1.5 × 10−18 at a 1000-s averaging time

Summary

Introduction

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. We demonstrate the capability of O-TWTFT to compare optical atomic clocks with transition frequencies that differ by over 90 THz. Second, we operate the O-TWTFT system in a new mode, allowing direct measurement of the frequency ratio of the two clocks.

Results

Conclusion