HYPERSENSITIVITY TO PERTURBATION IN THE QUANTUM KICKED TOP

For the quantum kicked top we study numerically the distribution of Hi lbert-space vectors evolving in the presence of a small random perturb ation. For an initial coherent state centered in a chaotic region of t he classical dynamics, the evolved perturbed vectors are distributed e ssentially like random vectors in Hilbert space. In contrast, for an i nitial coherent state centered near an elliptic (regular) fixed point of the classical dynamics, the evolved perturbed vectors remain close together, explore only a few dimensions of Hilbert space, and do not e xplore them randomly. These results support and extend the results of earlier studies, thereby providing additional support for a characteri zation of quantum chaos that uses concepts from information theory.