Researchers at AIST, in collaboration with researchers at Yokohama National University, have succeeded in generating a highly accurate time scale for 230 consecutive days by using an optical lattice clock.
Currently, a redefinition of the second is being discussed so that the optical frequency obtained using an optical clock will be used as the standard. Once the second is redefined, it is expected that a "graduated scale" tens of thousands of times finer than the current definition will be established, and that highly accurate time and frequency can be supplied to society. Many issues remain to be addressed in order to redefine the second, such as ensuring that the new definition is accurate and realized robustly over a long period compared with the current definition. Among them, the generation of a highly accurate and stable time scale by adjusting the frequency of an atomic clock based on an optical clock is considered as one of the conditions that are desired to be achieved for the redefinition of the second, and so research to incorporate an optical clock into a time scale is underway in many countries. AIST has been generating a time scale by manually adjusting the frequency of a hydrogen maser atomic clock, which is an atomic clock capable of continuous operation, but an even more accurate time scale can be expected to be generated by using an optical lattice clock. However, it has been difficult to accurately adjust the frequency of the atomic clock during the shutdown period of the optical lattice clock because the optical lattice clock could only be operated at a low uptime.
Using previously obtained data from an optical lattice clock that had been successfully operated at high uptime, the frequency of the hydrogen maser atomic clock was adjusted in a postprocessing analysis to generate a time scale based on the optical lattice clock. This time scale achieved the world's highest level of synchronization accuracy of within ±1 ns (one billionth of a second) from UTC, the international time standard, over a 230-day period. This achievement is expected to accelerate the consideration of the redefinition of the second.
Details of this technology have been published in Physical Review Applied on June 7, 2024 (EST).
Conceptual diagram of the generation of the current Time Frequency National Standard UTC (NMIJ) (top) and the future National Standard UTC (NMIJ) (bottom) using an optical lattice clock
Researchers at AIST, in collaboration with Yokohama National University, used two high-precision atomic clocks, an ytterbium optical lattice clock and a cesium fountain atomic clock, to search for dark matter, which exists in large amounts in the universe but whose true nature remains unknown.
AIST contributes to International Atomic Time, the international standard time, by operating the cesium fountain atomic clock, which realizes the definition of the unit of time "second," and the ytterbium optical lattice clock, one of the candidates for the redefinition of the second, at high operating rates for a long time. The frequency of an atomic clock is determined by fundamental physical constants such as the fine structure constant and electron mass, and the constant and invariant nature of the fundamental physical constants guarantees the accuracy of the atomic clock. On the other hand, it can be said that an atomic clock is an experimental device to verify whether the fundamental physical constants are truly constant and invariant.
Recently, ultra-light dark matter, which is more than 20 orders of magnitude lighter than the electron mass (about 9 × 10-31 kg), has been proposed as a candidate for dark matter. This very light dark matter behaves as a wave, not a particle. If dark matter waves interact with ordinary matter such as atoms, it is theoretically predicted that the fundamental physical constants will oscillate periodically, which in turn will cause periodic oscillations in the frequency of atomic clocks. In this study, we searched for such periodic oscillations in the frequency ratio data of the ytterbium optical lattice clock and the cesium fountain atomic clock. The results show that there is no such interaction between ultra-light dark matter in the mass range 10-58 kg to 10-56 kg and electrons, or if such an interaction exists, its strength is very weak. This result contributes to fundamental physics aimed at understanding dark matter.
Details of this study were published in Physical Review Letters on December 7, 2022.
Conceptual diagram of ultralight dark matter detection method using ytterbium (Yb) optical lattice clock and cesium (Cs) fountain atomic clock