Entropic measure of wave-packet spreading and ionization in laser-driven atoms

We consider wave-packet spreading and ionization of a one-dimensional model hydrogen atom interacting with a strong high-frequency laser field in the stabilization domain. We demonstrate the effect of the pulse shape on the dynamics in phase space and visualize our results with both the Wigner and the Q function phase-space quasiprobability representation. The Wehrl entropy is introduced and utilized as a convenient one-parameter measure of wave-packet spreading, phase-space localization, and ionization. © 1996 The American Physical Society.