Atom diffraction reveals the impact of atomic core electrons on atom-surface potentials

We measured ratios of van der Waals potential coefficients (C₃) for different atoms (Li, Na, K, and Rb) interacting with the same surface by studying atom diffraction from a nanograting. These measurements are a sensitive test of atomic structure calculations because C₃ ratios are strongly influenced by core electrons and only weakly influenced by the permittivity and geometry of the surface. Our measurement uncertainty of 2% in the ratio C3K/C3Na is close to the uncertainty of the best theoretical predictions, and some of these predictions are inconsistent with our measurement.