We are developing a new method for measuring microwave power based on frequency measurement. An atomic Rabi frequency is proportional to the microwave field strength. The microwave field strength is thus uniquely determined by the Rabi frequency. The new microwave power measurement using the Rabi frequency has the advantages over the present calorimeter system in terms of stability, time constant and ability for remote calibration. Furthermore, it is possible to check the consistency of microwave power unit derived from different methods (i.e. the Rabi frequency and the calorimetric methods).

The microwave magnetic field strength was measured using the Rabi frequency between microwave and gaseous cesium atoms in a glass cell. Transformation from the field strength into the absolute value of the power and comparison between the new microwave power measurement and the present standard will be performed in a later work.