Measurement of the Casimir Force between Dissimilar Metals

The first precise measurement of the Casimir force between dissimilar metals is reported. The attractive force, between a Cu layer evaporated on a microelectromechanical torsional oscillator and an Au layer deposited on an [Formula presented] sphere, was measured dynamically with a noise level of [Formula presented]. Measurements were performed for separations in the [Formula presented] range. The results agree to better than [Formula presented] in the [Formula presented] range with a theoretical model that takes into account the finite conductivity and roughness of the two metals. The observed discrepancies, which are much larger than the experimental precision, can be attributed to a lack of a complete characterization of the optical properties of the specific samples used in the experiment.