Optimizing coherent population trapping-based vapor-cell clocks for undersea use

Vapor-cell-based atomic clocks provide low power (<150 mW) atomic timing to GNSS-denied regions like the undersea Arctic, enabling applications like the acoustic sensing of polar climate change. However, they can suffer long-term fractional frequency drift of over 10^−10/month, preventing years-long deployment on the seafloor. We aim to develop a cesium vapor cell design with <10^-10/year drift in the temperature range (-4 to 10 C) relevant undersea. We report on numerically simulating and optimizing the signal contrast:linewidth ratio of the coherent population trapping (CPT) resonance, a key figure-of-merit for timing stability, in the vapor-cell parameter space. We also realized a tabletop cesium clock with interchangeable vapor cells at variable undersea temperatures, allowing preliminary measurement of the temperature coefficients for Ne and Ar buffer gasses that have mainly been reported in cells at or above 25 C. These approaches expand how we can understand vapor-cell clocks, and vapor-cell-based quantum sensors more broadly, to optimize their performance in new environments.