Quasiperiodicity versus mixing instability in a kicked quantum system

A two-level system subject to quasiperiodically modulated kicking is investigated under the aspects of ergodic theory. For weak kicking strength {κ} the correlation functions exhibit quasiperiodic behavior, whose character changes with increasing {κ} as recurrences become infrequent. A quantum instability with a transition to mixing behavior that was suggested for similar models does not arise. Analytic results are obtained for the case where two of three characteristic frequencies are incommensurate.