title: Stability of wave-packet dynamics under perturbations.
abstract: We introduce a method to investigate the stability of wave-packet dynamics under perturbations of the Hamiltonian. Our approach relies on semiclassical approximations, but is nonperturbative. Two separate contributions to the quantum fidelity are identified: one factor derives from the dispersion of the wave packets, whereas the other factor is determined by the separation of a trajectory of the perturbed classical system away from a corresponding unperturbed trajectory. We furthermore estimate both contributions in terms of classical Lyapunov exponents and find a decay of fidelity that is, generically, at least exponential, but may also be doubly exponential. The latter case is shown to be realized for inverted harmonic oscillators.
authors.affiliation: Abteilung Theoretische Physik, Universität Ulm, Albert-Einstein-Allee 11, D-89069 Ulm, Germany. jens.bolte@uni-ulm.de
authors.forename: Jens
authors.initials: J
authors.lastname: Bolte
authors.forename: Tobias
authors.initials: T
authors.lastname: Schwaibold