Progress on optical-clock-based time scale at NIST: Simulations and preliminary real-data analysis

This paper describes the recent National Institute of Standards and Technology (NIST) work on incorporating an optical clock into a time scale. We simulate a time scale composed of continuously operating commercial hydrogen masers and an optical frequency standard that does not operate continuously as a clock. The simulations indicate that to achieve the same performance of a continuously operating Cs-fountain time scale, it is necessary to run an optical frequency standard 12 minutes per half a day, or 1 hour per day, or 4 hours per 2.33 day, or 12 hours per week. Following the simulations, a Yb optical clock at NIST was frequently operated during the periods of 2017 March – April and 2017 late October – late December. During this operation, comb-mediated measurements between the Yb clock and a hydrogen maser had durations ranging from a few minutes to a few hours, depending on the experimental arrangements. This paper analyzes these real data preliminarily and discusses the results. More data are needed to make a more complete assessment.