Noise Induced Decoherence of Rydberg Atoms in a DC Field*

Application of a sudden field step to a Rydberg atom leads to creation of a Stark wavepacket whose evolution can be monitored using a half-cycle probe pulse applied after a variable time delay. We analyze the effects of noise on such wavepackets that is generated by quasi-randomly modulating the amplitude of the dc field. This noise induces decoherence which is manifested as a damping of the Stark quantum beats. We discuss the effects of different types of noise and present calculations and measurements for K(350p) atoms and ``colored'' noise, i.e., noise with a non-uniform power spectrum that possesses a characteristic frequency. We show that damping is most rapid when this frequency matches the orbital frequency of the Rydberg electron.