From coherent to noise-induced microwave ionization of Rydberg atoms

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Abstract
We present an experimental study of dynamical localization as displayed by rubidium Rydberg atoms ionized by a coherent microwave field. The ionization threshold field has been measured over a wide range of initial principal quantum numbers of the atomic Rydberg states, for a fixed interaction time of atom and field, and for two different values of the frequency of the microwave. Furthermore, fixing the initial state of the atoms and the microwave frequency, we studied the dependence of the ionization threshold on the interaction time. In both types of experiments, we identify a clear signature of dynamical localization and of its gradual destruction by noise. The transition from dynamical localization to diffusionlike ionization as weak broadband noise is added to the coherent microwave radiation is illustrated. In addition, we supply experimental evidence that suggests that a subset of the noise spectrum depending on the principal quantum number of the initial atomic Rydberg state is more relevant for the destruction of dynamical localization.