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VOLUME 92 (2010) | ISSUE 6 | PAGE 410
Dynamic and spectral mixing in nanosystems
In the framework of simple spin-boson Hamiltonian we study an interplay between dynamic and spectral roots to stochastic-like behavior. The Hamiltonian describes an initial vibrational state coupled to discrete dense spectrum reservoir. The reservoir states are formed by three sequences with rationally independent periodicities 1 ; 1 \pm \delta typical for vibrational states in many nanosize systems (e.g., large molecules containing CH2 fragment chains, or carbon nanotubes). We show that quantum evolution of the system is determined by a dimensionless parameter δ Γ , where Γ is characteristic number of the reservoir states relevant for the initial vibrational level dynamics. When δ Γ > 1 spectral chaos destroys recurrence cycles and the system state evolution is stochastic-like. In the opposite limit δ Γ < 1 dynamics is regular up to the critical recurrence cycle kc and for larger k > kc dynamic mixing leads to quasi-stochastic time evolution. Our semi-quantitative analytic results are confirmed by numerical solution of the equation of motion. We anticipate that both kinds of stochastic-like behavior (namely, due to spectral mixing and recurrence cycle dynamic mixing) can be observed by femtosecond spectroscopy methods in nanosystems in the spectral window 1011 - 1013 s-1 .