The interaction of charge carriers in superfluid helium with microwave fields - quantum dynamics of a classically chaotic system

We compare the classical and quantum descriptions of the response of charge carriers in superfluid helium to an external periodic perturbation. The classical dynamics displays chaotic features, whose main consequence is that the energy gain occurs via a diffusive process. Chaos is limited to the low-energy domain of phase space, and at high excitation energies the dynamics becomes progressively more regular due to the existence of an approximate constant of the motion. The quantum description shows the typical suppression of the classical diffusive energy growth and, at high energies, the quantum analogue of the classical constant of the motion dominates the quantum behaviour.