Double-resonance frequency shift in a hydrogen maser

We use the dressed-atom formalism to calculate the frequency shift in a hydrogen maser induced by applied radiation near the Zeeman frequency, and find excellent agreement with a previous calculation made in the bare-atom basis. The maser oscillates on the DF51, DmF50 hyperfine transition, while the applied field is swept through the F51, DmF561 Zeeman resonance. We determine the effect of the applied field on the Zeeman levels using the dressed-atom picture, and then calculate the maser frequency shift by coupling the dressed states to the microwave cavity. Qualitatively, the dressed-atom analysis gives a simpler physical interpretation of this double-resonance process, which has applications in precision hydrogen Zeeman spectroscopy, e.g., in fundamental symmetry tests.