Quantum stochasticity and unimolecular decay

Abstract

The origin of quantum stochasticity is studied via a simple model of decaying coupled anharmonic oscillators. It is shown that the decay rates of individual eigenstates, as well as mixed states, are never stochastic, even in regions where classical stochasticity exists. However, decay rates of (coherent) wave packets do show a transitional behavior, similar to the classical one, as the energy is raised. The transition is shown to arise from a competition between two rates, the dissociation rate, depending on the wave function amplitudes, and the dephasing rate, depending on the energy spectrum, and to occur when the dephasing becomes faster than the dissociation. It is suggested that only properties which depend simultaneously on the wave function‐amplitude and the energy spectrum can display this transitional behavior. It is also shown that strong coupling is not a necessary condition for stochasticity.