Loaded microwave cavity for compact vapor-cell clocks

Vapor-cell devices based on microwave interrogation provide a stable frequency reference with a compact and robust setup. Further miniaturization must focus on optimizing the physics package, containing the microwave cavity and atomic reservoir. In this paper, we present a compact cavity-cell assembly based on a dielectric-loaded cylindrical resonator. The loaded cavity resonating at 6.83 GHz has an external volume of only 35 cm3 and accommodates a vapor cell with 0.9 cm3 inner volume. The proposed design aims at strongly reducing the core of the atomic clock, maintaining at the same time high-performing short-term stability (σy(τ)≤5×10-13 τ-1/2 standard Allan deviation). The proposed structure is characterized in terms of microwave field uniformity and atom-field coupling with the aid of finite-elements calculations. The thermal sensitivity is also analyzed and experimentally characterized. We present preliminary spectroscopy results by integrating the compact cavity within a rubidium clock setup based on the pulsed optically pumping technique. The obtained clock signals are compatible with the targeted performances. The loaded-cavity approach is thus a viable design option for miniaturized microwave clocks.