Measurement of microwave magnetic field in free space using the Rabi frequency

Quantum-mechanics-based measurement of microwave magnetic field strength has been suggested and has attracted considerable research interest. Such measurements exploit the fact that the Rabi frequency, which indicates the degree of combination between atoms and microwaves, is proportional to the magnetic field strength of the microwaves interacting with the atoms. This new method is expected to facilitate realization of a quantum-based electromagnetic sensor that minimally perturbs the microwaves, being both nonmetal and wireless. This paper demonstrates measurement of the microwave magnetic field strength at a 9.2-GHz frequency using the Rabi frequency of cesium-133 atoms. The microwaves are radiated from a horn antenna.