Hydrogen maser flywheels for optical clocks

We consider the statistical and systematic uncertainties that arise from using a hydrogen maser as a flywheel oscillator for an intermittently operating optical clock. Diurnal delay variations observed in the distribution and measurement of the radiofrequency signals are the most significant effects for a clock that repeatedly operates at a similar time of day. In typical operation, we find an overall systematic uncertainty contribution u B/Lab = 2.0×10 −17 for the link between the clock and the reference timescale. Data obtained over more than two years of weekly characterization measurements confirms that the real-world behaviour of the flywheel hydrogen maser is in excellent statistical agreement with our stochastic model.