Multipole expansion for dispersion forces -- watch this trace

Abstract

Light-matter interaction models invariably rely on the multipole expansion of the electromagnetic potentials generated by complex charge distributions. These multipoles are typically taken to be traceless, however, for a correct evaluation of dispersion forces at all distances, the validity of this assumption has to be checked carefully. Here, we revisit the concept of dispersion forces on an atom near a dielectric surface from the perspective of macroscopic quantum electrodynamics and find that, beyond the quadrupole, the multipoles cannot always be taken as fully traceless. In particular, we show that the trace of the octupole moment contributes to Casimir-Polder interactions beyond the electrostatic regime.

6 pages, plus 4 pages supplementary material

References in corpus (8)

• Coherent Excitation of Rydberg Atoms in Thermal Vapor Microcells
• Exploring the van der Waals Atom-Surface attraction in the nanometric range
• Generation of cold Rydberg atoms at submicron distances from an optical nanofiber
• Thermal Casimir-Polder shifts in Rydberg atoms near metallic surfaces
• Spontaneous emission and energy shifts of a Rydberg rubidium atom close to an optical nanofiber
• Atom-surface physics: A review
• Measurement of the atom-surface van der Waals interaction by transmission spectroscopy in a wedged nano-cell
• Interaction of atomic systems with quantum vacuum beyond electric dipole approximation