  We numerically study influence of a polychromatic perturbation on wave acket
dynamics in one-dimensional double-well potential. It is found that
time-dependence of the tunneling probability shows two kinds of the motion
typically, coherent oscillation and irregular fluctuation, depending on the
perturbation parameters. The coherent motion changes the irregular one as the
increase of the strength and/or the number of frequency components of the
perturbation. We discuss a relation between our model and decoherence in
comparing with the result under stochastic perturbation. Furthermore we compare
the quantum fluctuation, tunneling in the quantum dynamics with ones in the
semiquantal dynamics.
