Fast-atom diffraction at surfaces

Fast helium atoms diffracted at alkali-halide surfaces under grazing angles of incidence exhibit intriguing diffraction patterns. The persistence of quantum coherence is remarkable, considering high surface temperatures and high (keV) kinetic energies of the incident atoms. Dissipative and decohering effects such as the momentum transfer between the incident helium atoms and the surface influence the diffraction patterns and control the width of the diffraction peaks, but they are weak enough to preserve the visibility of the diffration patterns. We perform an ab initio simulation of the quantum diffraction of fast helium beams at a LiF (100) surface in the (110) direction. Our results agree well with recent experimental diffraction data.