We present first experimental evidence for quantum reflection, originating exclusively from an attractive potential between an atom and a solid surface, at energies far from the threshold $E_i\to 0$. The system of light and stable ${}^3\mathrm{H}\mathrm{e}$ atoms scattering from an $\alpha$-quartz crystal allows confirmation of recent theory on quantum reflection up to its asymptotic behavior, determined by the nonretarded van der Waals potential $-C_3/r^3$. From the data, the gas-solid interaction potential is deduced quantitatively, covering the energy region, in which retardation plays a role.

• Received 7 November 2002

DOI:https://doi.org/10.1103/PhysRevLett.91.193202