Localization of eigenstates and mean Wehrl entropy

Dynamics of a periodically time-dependent quantum system is reflected in th e features of the eigenstates of the Floquet operator. Of the special impor tance, are their localization properties quantitatively characterized by th e eigenvector entropy: the inverse participation ratio or the eigenvector s tatistics. Since these quantities depend on the choice of the eigenbasis, w e suggest to use the overcomplete basis of coherent states, uniquely determ ined by the classical phase space. In this way, we define the mean Wehrl en tropy of eigenvectors of the Floquet operator and demonstrate that this qua ntity is useful to describe the quantum chaotic systems. (C) 2001 Elsevier Science B.V. All rights reserved.