Cavity-Q aging in the gas-cell atomic clock: studies with an atomic-candle signal

Slow variations in cavity Q and microwave power are thought to play a role in the long-term frequency stability of gas-cell atomic clocks. Here, we use an atomic-candle method to study the aging of a TE₀₁₁ microwave cavity´s resonant frequency and quality factor when a glass resonance cell containing Rb⁸⁷ loads the cavity. Our results suggest that the alkali vapor coats the inside glass surface of the resonance cell with a thin metallic film, and that as this film evolves the quality factor degrades. More generally, the present work demonstrates the efficacy of the atomic-candle method for investigating cavity resonances. In particular, we show that when used in conjunction with more traditional methods, the atomic-candle method has the potential to reveal information on a cavity mode´s spatial profile.