Abstract
Long-term frequency instabilities in vapor-cell clocks mainly arise from fluctuations of the experimental and environmental parameters that are converted to clock frequency fluctuations via various physical processes. Here, we discuss the frequency sensitivities and the resulting stability limitations at one-day timescale for a rubidium vapor-cell clock based on a compact magnetron-type cavity operated in air (no vacuum environment). Under ambient laboratory conditions, the external atmospheric pressure fluctuations may dominantly limit the clock stability via the barometric effect. We establish a complete long-term instability budget for our clock operated under stable pressure conditions. Where possible, the fluctuations of experimental parameters are measured via the atomic response. The measured clock instability of at one day is limited by the intensity light-shift effect, which could further be reduced by active stabilization of the laser intensity or stronger optical pumping. The analyses reported here show the way toward simple, compact, and low-power vapor-cell atomic clocks with excellent long-term stabilities ≤ 10-14 at one day when operated in ambient laboratory conditions.
Highlights
C OMPACT vapor-cell atomic clocks play a crucial role in many applications based on high-precision timing, such as satellite-based navigation and positioning systems [1], and synchronization in communications [2], [3] and power grids [4], [5]
We reported on our analyses of the long-term instability sources at the level of ≤10−14 in a compact Rb vapor-cell clock based on a time-domain Ramsey interrogation scheme with pulsed optical pumping and detection, in view of a highly compact atomic clock operating under ambient laboratory conditions with a strongly simplified physics package (PP)
We evaluated the longterm stability limitations at one-day timescale arising from various instability contributions due to typical experimental and environmental parameter fluctuations
Summary
C OMPACT vapor-cell atomic clocks play a crucial role in many applications based on high-precision timing, such as satellite-based navigation and positioning systems [1], and synchronization in communications [2], [3] and power grids [4], [5]. The physics package (PP) understudy in [17] includes a microwave cavity with a high-quality factor (Q ≈ 10 000) placed in vacuum Such high-Q of the cavity is crucial for clock signal detection in the microwave domain, but can seriously limit the clock stability through the cavity-pulling effect [18], which, in this case, presents the dominant instability source arising from fluctuations in microwave power and external pressure. For this clock prototype, we have previously demonstrated short-term stability of 2.1 × 10−13 at 1 s averaging time, limited by the signal-to-noise ratio (SNR) of the optically detected signal [10], and reduced lightshift instability contributions [21]. While we report on the long-term stability limits for our POP Rb vapor-cell clock, many relevant physical processes are similar for vapor-cell clocks operated with other interrogation schemes (CW-DR, CPT, Ramsey-CPT, etc.)
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