Frankfurt 2006 – scientific programme

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Q: Quantenoptik und Photonik

Q 3: Gruppenberichte Quanteneffekte

Q 3.3: Group Report

Monday, March 13, 2006, 12:10–12:40, HI

Microscopic origin of Casimir-Polder forces — •Stefan Yoshi Buhmann and Dirk-Gunnar Welsch — Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany

Dispersion forces between polarizable objects are a well-known consequence of the vacuum fluctuations of the electromagnetic field. One usually distinguishes between the van der Waals force between two atoms, the Casimir-Polder force between an atom and a macroscopic body, and the Casimir force between two bodies, where the distinction is made between microscopic point-like atoms on the one hand and macroscopic magnetodielectric bodies, which within the frame of macroscopic quantum electrodynamics are characterized by smoothly varying permittivities and permeabilities, on the other hand. Within the frame of macroscopic quantum electrodynamics, the Casimir-Polder force on a ground-state atom placed within an arbitrary arrangement of magnetodielectric bodies can be given in terms of the polarizability of the atom and the scattering Green tensor of the body-assisted electromagnetic field. We present a general proof that the Casimir-Polder force calculated in this way can be rewritten as an infinite series of microscopic many-atom van der Waals forces, for which explicit expressions are derived. The proof, which bridges the gap between the macroscopic and the microscopic description, is based on the Born expansion of the Green tensor together with the Clausius-Mosotti law, which relates the permittivity of the body to the polarizability of its atomic constituents. To illustrate our result, we explicitly show that the leading two-atom contribution is identical to the expression that can be derived from fourth-order perturbation theory.