Determination of the Microwave Field Strength Using the Rabi Oscillation for a New Microwave Power Standard

This paper describes the development of a new type of microwave power standard based on atomic resonances. An atomic Rabi frequency is proportional to the magnetic field strength of the resonant microwave; the proportionality constant is determined only from fundamental constants and atomic quantum theory. The microwave field strength that corresponds to microwave power is thus uniquely determined by the Rabi frequency. The proportionality constant can thus serve as the basis for a new microwave power standard. This paper confirmed that the Rabi frequency of cesium-133 (¹³³Cs) atoms in a rectangular cell is proportional to the incident microwave field strength. A rectangular Cs glass cell was developed and inserted into a WR90 waveguide-an industrially practical waveguide that permits the impedance analysis necessary to measure microwave power. The microwave field strength in the Cs cell can be adjusted to arbitrary values proportional to the Rabi frequency. The relative expanded uncertainties of the effective microwave magnetic field strength H _eff for the coverage factor k = 2, which is typically less than 7%, averaged 4%. The dynamic range of the available Rabi frequency was 31.9 dB.