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

TLDR

Time scales rely on atomic frequency standards and a local oscillator, yet optical clocks—despite their superior accuracy—have not been used for time scale generation, and TT(BIPM) is computed annually from weighted averages of TAI evaluations using primary and secondary standards. The study aimed to realize a continuously generated, optically steered time scale TA(Sr) by steering an oscillator with intermittent operation of a 87 Sr optical lattice clock over half a year. They steered an oscillator with intermittent 87 Sr optical lattice clock operation to generate TA(Sr) continuously for six months and compared it to TT(BIPM16). TA(Sr) matched TAI’s stability at the 10⁻¹⁶ level, differed from TT(BIPM16) by only 0.79 ns after five months, and enabled one‑month mean TAI evaluations over six months with uncertainties comparable to primary frequency standards.

Abstract

Abstract 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 87 Sr optical lattice clock, we realized an “optically steered” time scale TA(Sr) that was continuously generated for half a year. The resultant time scale was as stable as International Atomic Time (TAI) with its accuracy at the 10 −16 level. We also compared the time scale with TT(BIPM16). TT(BIPM) is computed in deferred time each January based on a weighted average of the evaluations of the frequency of TAI using primary and secondary frequency standards. The variation of the time difference TA(Sr) – TT(BIPM16) was 0.79 ns after 5 months, suggesting the compatibility of using optical clocks for time scale generation. The steady signal also demonstrated the capability to evaluate one-month mean scale intervals of TAI over all six months with comparable uncertainties to those of primary frequency standards (PFSs).