Optical Timescale

Since optical clocks have smaller uncertainties than microwave clocks, there are discussions to use them in a redefinition of the SI second. But to do that, the second-by-second tick of everyday life then still has to maintain its accuracy and reliability. For this purpose, we are working on algorithms to fine-tune the output frequency of a hydrogen maser based on calibrations by an optical clock [1]. On the basis of this research, Japan Standard Time (JST) is now already generated with increased accuracy according to the frequency measurements of our strontium optical lattice clock. The figure below shows the time difference between JST and Coordinated Universal Time (UTC). The reduced time difference shows the increased accuracy of Japan Standard Time since September 2021, when its frequency started to be adjusted by the optical lattice clock.

Although currently a hydrogen maser is used as the source oscillator of the time signal, it is expected that this will ultimately be replaced by a laser, to realize an all-optical time system. A laser referenced to an ultra-stable optical cavity has a much smaller amount of short-term frequency fluctuations, such that an all-optical time system can achieve higher stability than the current microwave systems over the entire range from short to long term.

1) H. Hachisu, F. Nakagawa, Y. Hanado and T. Ido, Months-long real-time generation of a time scale based on an optical clock, Sci. Rep. 8 4243 (2018)