Casimir interaction between a dielectric nanosphere and a metallic plane

We study the Casimir interaction between a dielectric nanosphere and a metallic plane, using the multiple scattering theory. Exact results are obtained with the dielectric described by a Sellmeier model and the metal by a Drude model. Asymptotic forms are discussed for small spheres and large or small distances. The well-known Casimir-Polder formula is recovered at the limit of vanishingly small spheres, while an expression that behaves better at small distances is found for any finite value of the radius. The exact results are of particular interest for the study of quantum states of nanospheres in the vicinity of surfaces.