Global Optical Clock Network Paves Way for Redefining the Second

Researchers have conducted the most extensive coordinated comparison of optical clocks to date, simultaneously operating clocks and links across six countries. This experiment, spanning thousands of kilometers, represents a significant step towards redefining the second and establishing a global optical time scale. Using both satellite and optical fiber links, the study highlights areas for improvement in optical clock precision and reliability. The findings are crucial for advancing next-generation optical clocks and scientific endeavors reliant on precise time and frequency measurements, ultimately aiming to leverage the superior accuracy of optical clocks to redefine the second in the International System of Units.