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Optical-Clock-Based Time Scale



Jian Yao, Jeffrey A. Sherman, Tara M. Fortier, Andrew D. Ludlow, Holly Leopardi, Thomas E. Parker, William F. McGrew, Scott A. Diddams, Judah Levine


A time scale is a procedure for accurately and continuously marking the passage of time. It is exemplified by coordinated universal time (UTC), and provides the backbone for critical navigation tools such as the global positioning system (GPS). Present time scales employ microwave atomic clocks, whose attributes can be combined and averaged in a manner such that the composite is more stable, accurate, and reliable than the output of any individual clock. Over the past decade, clocks operating at optical frequencies have been introduced which are orders of magnitude more stable than any microwave clock. However, in spite of their great potential, these optical clocks cannot be operated continuously, which makes their use in a time scale problematic. In this paper, we report the development of a new hybrid microwave- optical time scale, which only requires the optical clock to run intermittently while relying upon the ensemble of microwave clocks to serve as the flywheel oscillator. This time scale, for the first time, demonstrates sub-nanosecond accuracy for a few months, attaining a fractional frequency uncertainty of 1.4x10−16 at 30 days and reaching the 10−17 decade at 50 days, with respect to UTC. This time scale significantly improves the accuracy in time keeping and could profoundly change the existing time-scale architectures.
Physical Review Applied


Cs fountain, Hydrogen maser, Kalman filter, Optical clock, Time scale, UTC


Yao, J. , Sherman, J. , Fortier, T. , Ludlow, A. , Leopardi, H. , Parker, T. , McGrew, W. , Diddams, S. and Levine, J. (2019), Optical-Clock-Based Time Scale, Physical Review Applied (Accessed May 23, 2024)


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Created October 29, 2019, Updated October 6, 2020