Quantum Evaporation from Superfluid Helium at Normal Incidence

TL;DR

This paper investigates how atoms, rotons, and phonons interact with the free surface of superfluid helium-4, providing a unified framework to predict evaporation, condensation, and reflection probabilities based on scattering theory.

Contribution

It introduces a novel approach to relate all scattering probabilities at the helium surface to a single energy-dependent parameter using unitarity and time-reversal symmetry.

Findings

All nonzero scattering probabilities can be expressed via one energy-dependent parameter.

Quantitative predictions are achieved with linearized time-dependent density functional theory.

The study advances understanding of atom and quasiparticle interactions at superfluid helium surfaces.

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.