Nonperturbative resonances in periodically driven quantum wells

Energy absorption characteristics are computed for a classical and a quantum model of an infinite square well, as a function of driving amplitude and frequency. Nonperturbative resonances are observed corresponding to the replacement of states localized in phase space by more extended states. Their presence is predicted by avoided crossings in the quasienergy spectrum of the Floquet operator. The conditions under which these resonances occur can be realized in experiments on GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells in intense far-infrared radiation.