QUANTUM-MECHANICAL DIFFUSION IN COMPLEX SURROUNDINGS

The dynamics of a classical, heavy system coupled to a quantum mechani cal light system is studied in a simple time-dependent random matrix m odel, where the degree of complexity can be changed by a ''chaoticity parameter.'' It is shown that the energy of the quantum mechanical sys tem diffuses as it interacts with the classical system, providing it i s chaotic, while a ballistic behavior appears in the ordered case. The energy diffusion of the chaotic system saturates, and it is shown tha t the saturation time is related to short-range correlations in the en ergy spectrum. In mixed systems the propagation of energy changes from a ballistic to diffusive behavior at a time related to long-range ene rgy correlations.