Coordinated international comparisons between optical clocks connected via fiber and satellite links

TL;DR

This study presents the largest coordinated international comparison of optical clocks using fiber and satellite links, achieving unprecedented measurement precision and supporting the redefinition of the second.

Contribution

It is the first to measure 38 optical frequency ratios across multiple countries with improved accuracy using combined fiber and satellite links.

Findings

Four ratios measured directly for the first time

Lower uncertainties achieved in existing ratios

Supports redefinition of the second and optical standards

Abstract

Optical clocks provide ultra-precise frequency references that are vital for international metrology as well as for tests of fundamental physics. To investigate the level of agreement between different clocks, we simultaneously measured the frequency ratios between ten optical clocks in six different countries, using fiber and satellite links. This is the largest coordinated comparison to date, from which we present a subset of 38 optical frequency ratios and an evaluation of the correlations between them. Four ratios were measured directly for the first time, while others had significantly lower uncertainties than previously achieved, supporting the advance towards a redefinition of the second and the use of optical standards for international time scales.