Microwave multiphoton Rabi oscillations.

Resonant multiphoton transitions are driven between the 21s state and the lowest energy member of the adjacent n = 19 Stark manifold in Potassium using a high intensity 9 GHz microwave field generated inside a resonant cavity. Using the linear Stark shift of the manifold state the levels can be tuned into resonance by applying a static voltage to a septum inside the cavity. Atoms are first excited to the 21s state by a laser while the microwave field is resonant. Some time later a voltage pulse applied to the cavity detunes the atoms from resonance. A high voltage pulse is then applied to ionize only the excited n = 19 atoms, which are then detected. Oscillations in the n = 19 population are observed as a function of the time the atoms spend in resonance.