Quantum Evaporation from LiquidHe4by Rotons

Abstract

We have shown that rotons as well as phonons can evaporate ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ atoms in a single-quantum process. Measurements of the time of flight and the angular distribution of the evaporated atoms clearly distinguish between evaporation by phonons and rotons. The results indicate that energy and the parallel component of momentum are conserved at the free liquid surface.