Quantum-Based Microwave Power Measurements: Proof-of-Concept Experiment
Thomas P. Crowley, E. A. Donley, T P. Heavner
An initial proof-of-concept experiment to measure microwave power based on quantum-mechanical principles is presented. Ground state cesium atoms exposed to 9.192631770 GHz microwave oscillate between two hyperfine states at a rate that is proportional to the RF magnetic field strength. This provides a traceability path for RF field strength that depends only on the fundamental parameters in the proportionality constant. A mini-fountain apparatus was used to prepare laser-cooled cesium atoms in a single hyperfine state which were then launched through a cylindrical cavity operating in the TE 011 mode. After passing through the cavity, the percentage of atoms in the two hyperfine states was measured. Rabi oscillations between the two states were observed as a function of microwave field strength. The scaling with field strength and with time in the cavity agreed with theory to within 0.4%. The field strength in the cavity was used along with measured S parameters to determine the microwave power incident at a reference plane outside the fountain apparatus. The difference between the quantum-based microwave power measurement and a traditional microwave power measurement was less than 5% of the measured power.