Using the minimum uncertainty state of quantum integrable system Ho as init
ial state, the spatiotemporal evolution of the wave packet under the action
of perturbed Hamiltonian is studied causally as in classical mechanics. Du
e to the existence of the avoided energy level crossing in the spectrum the
re exist nonlinear resonances between some pairs of neighboring components
of the wave packet, the deterministic dynamical evolution becomes very comp
licated and appears to be chaotic. It is proposed to use expectation values
for the whole set of basic dynamical variables and the corresponding sprea
ding widths to describe the topological features concisely such that the qu
antum chaotic motion can be studied in contrast with the quantum regular mo
tion and well characterized with the asymptotic behaviors. It has been demo
nstrated with numerical results that such a wave packet has indeed quantum
behaviors of ergodicity as in corresponding classical case.