Realizing a coherent population trapping-based vapor cell clock at low temperatures

Robust, compact, atomic frequency references that operate on low power (<150 mW) underpin many applications requiring long-term timing outside ideal laboratory conditions. For example, acoustic sensing under Arctic oceans provides critical information for understanding climate change but requires years-long timing and continuous operation on batteries. Arctic temperatures, however, prevent simple leveraging of quartz crystals and low power atomic frequency references. Vapor-cell based chip-scale atomic clocks and Coherent Population Trapping resonances can suffer from low signal contrast and temperature dependent shifts. Here, we realize a table-top, CPT-based cesium vapor cell clock to study temperature's effect on the CPT signals in the range (-4 to 10 C) relevant for many undersea applications. We also study temperature's effect on our clock's short-term stability. Along the way, we adapt models to predict absorbance lineshapes and CPT signals for the Cs D2 transition. Our objectives are to understand the science and technology of low-power atomic clock designs that could better optimize performance for undersea applications.