Quantum Evaporation from Superfluid Helium at Normal Incidence

Abstract

We study the scattering of atoms, rotons and phonons at the free surface of ${}^4$He at normal incidence and calculate the evaporation, condensation and reflection probabilities. Assuming elastic one-to-one processes and using general properties of the scattering matrix, such as unitarity and time reversal, we argue that all nonzero probabilities can be written in terms of a single energy-dependent parameter. Quantitative predictions are obtained using linearized time dependent density functional theory.

12 pages, REVTeX, 2 postscript figures, available also at http://anubis.science.unitn.it/~dalfovo/papers/papers.html