Frequency ratio of an In ion clock and a Sr optical lattice clock.

We report on the first, to the best of our knowledge, frequency ratio measurement of an singleion clock and a optical lattice clock. A hydrogen maser serves as a flywheel oscillator to measure the ratio by independent optical combs. From 89,000 s of measurement time, the frequency ratio / is determined to be 2.

New bounds on dark matter coupling from a global network of optical atomic clocks.

We report on the first Earth-scale quantum sensor network based on optical atomic clocks aimed at dark matter (DM) detection. Exploiting differences in the susceptibilities to the fine-structure constant of essential parts of an optical atomic clock, i.e.

Advanced Satellite-Based Frequency Transfer at the 10 Level.

Advanced satellite-based frequency transfers by two-way carrier-phase (TWCP) and integer precise point positioning have been performed between the National Institute of Information and Communications Technology and Korea Research Institute of Standards and Science. We confirm that the disagreement between them is less than at an averaging time of several days. In addition, an overseas frequency ratio measurement of Sr and Yb optical lattice clocks was directly performed by TWCP.

Months-long real-time generation of a time scale based on an optical clock.

Time scales consistently provide precise time stamps and time intervals by combining atomic frequency standards with a reliable local oscillator. Optical frequency standards, however, have not been applied to the generation of time scales, although they provide superb accuracy and stability these days. Here, by steering an oscillator frequency based on the intermittent operation of a Sr optical lattice clock, we realized an "optically steered" time scale TA(Sr) that was continuously generated for half a year.

SI-traceable measurement of an optical frequency at the low 10 level without a local primary standard.

SI-traceable measurements of optical frequencies using International Atomic Time (TAI) do not require a local primary frequency reference, but suffer from an uncertainty in tracing to the SI second. For the measurement of the Sr lattice clock transition, we have reduced this uncertainty to the low 10 level by averaging three sets of ten-day intermittent measurements, in which we operated the lattice clock for 10 s on each day. Moreover, a combined oscillator of two hydrogen masers was employed as a local flywheel oscillator (LFO) in order to mitigate the impact of sporadic excursion of LFO frequency.