On January 16, 2025, researchers announced a significant advancement in optical atomic clocks, a development that could redefine the fundamental unit of time, the second. This new approach surpasses the long-standing cesium-based definition established in 1967, with the potential for a more precise measurement of time.
In recent years, scientists have demonstrated the capability of designing clocks that are 1,000 times more accurate than their atomic counterparts. However, a major hurdle in this redefinition process has been the challenge of comparing different clocks with sufficient precision. Traditional frequency ratio measurements between clocks can take several days, complicating the redefinition efforts.
The newly developed multi-ion clock design addresses this issue through its scalability; measuring with ten ions allows for ten times faster comparisons. This innovation is a crucial step toward achieving the benchmark required for redefining the second, as the team successfully measured a frequency ratio of less than five parts per billion billion.
Professor Tanja Mehlstäubler emphasized the importance of this achievement, stating, "We really broke a true world record because nobody so far compared two types of optical clocks at that level!" This accomplishment is not merely a milestone but a starting point, as theoretical models suggest that the multi-ion clock could further reduce measurement uncertainty.
The implications of this research extend beyond redefining time. These advanced clocks are sensitive to minute gravitational effects, enabling them to monitor subtle changes in the Earth's motion and elevation due to environmental changes, such as glacial melting. They could also enhance our understanding of the fundamental principles of physics, particularly in the realms of general relativity and quantum mechanics.
Dr. Jonas Keller, a lead author of the study, noted the ongoing potential for these systems, stating, "The system still has a lot more potential. It can go down to 1x10 in systematic uncertainty as we've shown in principle." The research team’s paper detailing these findings was published in the journal Physical Review Letters.