Some of the contents of this article have been adapted from the publication of the Laboratoire Temps-Espace (LTE), Observatoire de Paris-PSL.
Optical clocks : a new frontier in time measurement
The new generation of atomic clocks, known as optical clocks, exceed the precision of current standards by several orders of magnitude. Their performance opens the way to new scientific fields, such as chronometric geodesy - a method of measuring altitude differences by the difference in rhythms of distant clocks - or the improvement of space-time reference systems, essential to many scientific services and observation systems, both on Earth and in space. But their extreme stability makes conventional clock comparison methods obsolete.
A worldwide network for ultra-precise comparisons
The remarkable stability of optical clocks, however, makes traditional methods of comparison unsuitable. In response, researchers have used optical fibers that ensure symmetrical light propagation in both directions, guaranteeing faithful signal transmission over thousands of kilometers. Combined with state-of-the-art satellite links, these technologies made it possible to simultaneously link and compare ten clocks spread over several countries.
A major breakthrough in metrology
A total of 38 frequency ratios were measured between optical clocks, some for the first time, with record levels of uncertainty. These results constitute the most extensive and accurate comparison ever carried out, and represent a major step towards the integration of optical clocks into the international definition of atomic time.
Applications in astronomy, geodesy and metrology
These future optical time scales will make it possible to detect extremely small temporal differences between signals received at distant sites, a valuable asset for multi-messenger astronomy. They will also enable dynamic mapping of the Earth’s gravitational field using relativistic geodesy, and improve the accuracy of VLBI observations. Finally, time-frequency metrology will benefit directly from these new, more stable and precise references.