Long-Term Stability Analysis Toward <10⁻¹⁴ Level for a Highly Compact POP Rb Cell Atomic Clock

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 <2 × 10 −14 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.

Metrological and stability studies in high-performance rubidium vapor-cell atomic clocks

“…Finally, we present and discuss the measured clock frequency instability. Sections 3.3 and 3.4 are essentially based on our article [113]. The text and figures in these two sections are adapted from [113].…”

“…A stability level below 10 µK over one day is determined for both cell and stem, which would lead to a clock stability limit well below 10 −16 due to the buffer-gas collisions. The right axis in Figure 3 [113] and includes additional data.…”

“…Analysis of long-term clock instability sources Clock frequency shift as a function of the applied C-field, the second-order Zeeman shift ∆ν Z e .Figure adaptedfrom[113].…”

“…Stability analysis performed using ThêoH statistics (cf. section 1.6.1); filled markers: overlapping Allan deviation; empty markers: Thêo1.Figure adapted from[113].…”

“…MeasurementPoly-fit: f (T) = a 0 + a 1 (T -T 0 ) + a 2 (T -T 0 ) Clock frequency shift as a function of the clock cell temperature, the buffer-gas density shift ∆ν BG .Figure adaptedfrom[113].…”