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
Researchers at AIST, in collaboration with Ibaraki University, have demonstrated the feasibility of "spring-water temperature difference power generation" using the temperature difference between spring water and the ambient air. By using the generated electricity, the temperature of spring water can be measured without batteries, and the data can be collected automatically via wireless communication. This technology uses thermoelectric power generation, which is an interconversion of heat and electricity in a solid, so it does not require moving parts such as a water wheel, and power can be generated even in waterways where there is no water flow. It can also generate power continuously in the shade where sunlight does not reach and at night. This technology also enables continuous environmental measurement with low maintenance costs and early detection of changes in spring water caused by human activities. By creating multifaceted value by utilizing the thermal energy of spring water as electric power, this technology is expected to contribute to the conservation and sustainable use of spring water as a local resource.
Principle of spring-water temperature difference power generation