Cavity-Q aging observed via 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. (In our experiments the quality factor changed by approximately 30% over a timescale of months.) 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.