Measured Impact of core electrons on Van der Waals potentials

We measured atom-surface Van der Waals potentials ($C_{3}$ coefficients) for Li, Na, K, and Rb atoms by studying diffraction from a nanograting. By focusing on ratios of $C_{3}$, we eliminate systematic errors due to the geometry and roughness of the nanograting. We measured the ratio $C_{3}^{K} / C_{3}^{Na} = 1.544 \pm 0.025$ meVnm$^{3}$. With this $2\%$ precision, our measurements reveal the contribution of core-electrons to atom-surface interactions. We also show that the permittivity $\epsilon(\omega)$ of the surface does not significantly affect the ratios of $C_{3}$. Therefore our results serve as a good test of atomic structure calculations.