QUANTUM INTERFERENCE IN HALF-CYCLE MICROWAVE MULTIPHOTON TRANSITIONS

We observe microwave multiphoton transitions in Rydberg states of Na u sing intense subnanosecond half-cycle electric field pulses in a micro wave transmission line. Transition probabilities from ns and n*d stat es, ranging in principal quantum number from 18 to 40, to nearby nl ( greater than or equal to 22) states are measured both as a function of pulse amplitude and the delay between two identical temporally spaced pulses. The transition rate depends strongly on both the pulse amplit ude and the temporal delay between the two pulses. Nearly 100% of the population can be transferred for certain amplitudes of the half-cycle pulse. Transition probabilities are successfully described both with a dynamic Stark model and direct numerical integration of the time-dep endent Schrodinger equation. Ramsey interference between two delayed p ulses is observed that shows strong-field behavior. The two-pulse expe riment is a technique for high-order multiphoton spectroscopy without concern for ac Stark shifts.