Nonperturbative analysis of a model quantum system under time periodic forcing

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We analyze the time evolution of a one-dimensional quantum system with an attractive delta function potential whose strength is subjected to a time periodic (zero mean) parametric variation. We show that for generic forcing which includes the sum of any finite number of harmonics, the system, started in a bound state will get fully ionized for large t irrespective of the magnitude or frequency of the forcing. There are however exceptional, very non-generic forcings that do not lead to full ionization. These include rather simple explicit periodic forcings for which the system evolves to a nontrivial localized stationary state related to eigenfunctions of the Floquet operator.