Measurement of the van der Waals force using reflection of cold atoms from magnetic thin-film atom mirrors

We report on a measurement of the van der Waals interaction between rubidium atoms in the ground state and a metallic surface, employing a new method involving reflection of laser-cooled atoms from magnetic thin-film atom mirrors. We made use of the fact that the typical distance from which atoms reflect from thin-film magnetic mirrors is of the order of the magnetic domain size and the thickness of the thin film. The modification of the reflectivity of cold atoms from cobalt thin-film magnetic mirrors, with thickness in the range of 200-20nm, due to the competition between the attractive atom-surface interaction and the repulsive magnetic interaction enabled the measurement of the van der Waals force in the range 20-50nm with an uncertainty of 15%. The measured value agrees well with recent theoretical estimates.