Atomic Microwave Power Standard Based on the Rabi Frequency

The Rabi frequency for an atomic hyperfine structure transition is proportional to the magnetic field strength of the incident electromagnetic wave. Using the known proportionality constant, an atomic microwave power standard based on the Rabi frequency can be realized. In this paper, the Rabi frequency of cesium atoms in a glass cell inserted in a microwave waveguide was measured using the atomic-candle method. The Rabi frequency was converted into the incident microwave power via the magnetic field strength by correcting the effects of the glass cell and impedance mismatch. The relative expanded uncertainty was approximately 4% at a coverage factor of 2. The microwave power measured from the Rabi frequency was compared with that measured by a calorimetric method. These results coincided within their uncertainties.