Specular Reflection of Very Slow Metastable Neon Atoms from a Solid Surface

An ultracold narrow atomic beam of metastable neon in the ${1s}_3\left[\right(2s{)}^{5}3p:{}_{}{}^1{}_{}{}^{}P_0^{}{}_{}{}^{}]$ state is used to study specular reflection of atoms from a solid surface at extremely slow incident velocity. The reflectivity on a silicon (1,0,0) surface and a BK7 glass surface is measured at the normal incident velocity between $1\mathrm{mm}/\mathrm{s}$ and $3\mathrm{cm}/\mathrm{s}$. The reflectivity above $30\%$ is observed at about $1\mathrm{mm}/\mathrm{s}$. The observed velocity dependence is explained semiquantitatively by the quantum reflection that is caused by the attractive Casimir–van der Waals potential of the atom-surface interaction.