Global Test for New Time Standard

Researchers from various countries have conducted the largest head-to-head comparison of atomic clocks in an effort to prepare for the redefinition of the second, anticipated to occur around 2030.

Summary of Key Points

• Definition of the Second: The current duration of a second is defined by caesium (Cs) atomic clocks, measuring the radiation emitted by Cs atoms. The present standard was established in 1967 and defined as the duration of 9,192,631,770 periods of microwave radiation from Cs atoms.

• Transition to Optical Clocks: The precision of Cs atomic clocks is being challenged by the next generation of optical clocks, which can measure time up to 18 decimal places and potentially offer greater stability. Optical clocks, such as those employing strontium and ytterbium ions, utilize radiation frequencies in the optical range, which is significantly higher than that of microwave frequencies.

• Comparative Testing: In this study, 10 optical atomic clocks were tested across three continents (Europe and Japan), involving 65 researchers. This sophisticated setup aimed to verify that these clocks agree to an unprecedented degree, which is crucial for a future global time standard.

• Methodology: Scientists utilized existing telecommunications technologies to connect the optical clocks. This included using optical fibers in France, Germany, and Italy, and an advanced GPS technique called integer precise point positioning (IPPP) for longer distances, such as across the English Channel to Japan.

• Data Collection and Results: During the testing from February 20 to April 6, 2022, researchers collected 38 independent optical-frequency ratios. The results demonstrated an agreement among the clocks within an accuracy of 10^-16 to 10^-18, identifying the robustness of methods linking these diverse setups.

• Issues and Future Work: Discrepancies were noted in the performances of the clocks, such as a notable glitch with the Italian Yb clock relative to fiber measurements, indicating areas that need further investigation before the redefinition of the second.

• Significance for Technology: Atomic clocks play a vital role in modern technologies, including GPS systems (American, Russian, European, and Indian), radio astronomy, and climate science, necessitating highly accurate timekeeping.

• Contributions to Science: The study emphasizes the importance of large-scale collaborative research in troubleshooting and refining time standards. It also highlights how advancements in optical clocks could fundamentally upgrade the precision of time measurements globally.

• Publication: The findings of this extensive study were published in the journal Optica on June 12, providing a framework for future work necessary to redefine the second with the emerging optical clock standards.

Conclusion

This comprehensive comparative testing of optical clocks represents a significant step towards the upcoming transition in defining the second, with critical implications for various scientific and technological applications. The cooperation demonstrated across international institutions showcases the collaborative effort required to advance our measurement systems in precision timing, ensuring they meet the demands of evolving technology.