Unprecedented optical clock network lays groundwork for redefining the second

Summary

Strontium optical lattice clock at NPL. Credit: Andrew Brookes In a new study, researchers carried out the most extensive coordinated comparison of optical clocks to date by operating clocks and the links connecting them simultaneously across six countries. Spanning thousands of kilometers, the experiment represents a significant step toward redefining the second and ultimately establishing a global optical time scale. "The accurate time and frequency signals provided by atomic clocks are essential for many everyday technologies—like GPS, managing power grids and keeping financial transactions in sync," said Helen Margolis, head of time and frequency at the National Physical Laboratory (NPL) in the United Kingdom. "Our findings could help to improve the performance of next-generation optical clocks, unleashing entirely new applications and advancing scientific endeavors that rely on time and frequency." Optical clocks are a type of atomic clock that uses lasers to excite atoms in a controlled way that causes the atoms to shift between specific energy levels. These shifts happen at very precise frequencies, which serve as the "ticks" of the clock. Because these clocks come in various forms, each using different atoms to keep time, realizing the full potential of these precision timekeepers requires comparing them across long distances. In Optica, a multi-institutional group of researchers reports results from 38 comparisons—or frequency ratios—performed simultaneously with ten different optical clocks. Four of these comparisons were conducted directly for the first time, and many of the others were measured with much greater accuracy than before. "These measurements provide critical information about what work is still needed for optical clocks to achieve the precision and reliability required for use in international timekeeping," said Marco Pizzocaro, senior researcher at the Instituto Nazionale Di Ricerca Metrologica (INRiM) in Italy. "Our experiment also showed h...