Atoms to Quanta - Quantum Evaporation and Condensation

Abstract

Light waves carry quantised energy and momentum. The analogous quantisation of sound waves in condensed matter into phonons, with quanta of energy and momentum is straightforward. A very direct confirmation of this quantisation comes from the quantum evaporation of helium atoms from the surface of superfluid helium by experimentally generated phonons, or other ballistic excitations in the liquid, in a one-to-one process of energy and momentum transfer from quanta to individual atoms.