Molecular quantum wave-packet splitting and revivals in shared phase space

Abstract

The evolution of a molecular wave packet created by an ultrashort laser pulse in a system of two coupled bound states is investigated by quantum dynamics calculations and semiclassical theory. Under suitable dynamical quantum interference conditions, the wave packet may be split into two separable fractions that move in different but partially overlapping regions of the energetically available phase space. Each wave-packet part can be individually addressed in the divided parts of the molecular phase space, and they are shown to go through separate long-term collapse-revival cycles analogous to those of wave packets moving in single anharmonic potentials. In a pump-probe scheme, the dynamics of the system would look very different depending on what internuclear distances are probed. The regular dynamics observable in the separated parts of the phase space takes on a quite irregular appearance in the regions that are shared by the wave-packet components. The wave-packet regularity is shown to depend sensitively on the pump pulse wavelength, which is a reflection of the energy range over which the quantum interference conditions are maintained. These conditions, as well as the wave-packet fraction revival times, are well reproduced by semiclassical theory.