Experimental observation of quantum reflection far from threshold

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 [Formula presented]. The system of light and stable [Formula presented] atoms scattering from an [Formula presented]-quartz crystal allows confirmation of recent theory on quantum reflection up to its asymptotic behavior, determined by the nonretarded van der Waals potential [Formula presented]. From the data, the gas-solid interaction potential is deduced quantitatively, covering the energy region, in which retardation plays a role. © 2003 The American Physical Society.