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Van der Waals interactions in confined geometries

Dispersion forces such as Casimir, Casimir-Polder and van der Waals forces arise due to fluctuations of the quantised electromagnetic field. Any alteration of the environment in which the (virtual) photons propagate leads invariably to a modification of the respective interaction. Waveguide structures in particular are known to resonantly enhance Casimir-Polder interactions [1]. Here we focus on the van der Waals interaction between two isolated atoms inside a cylindrical waveguide and its applications to tunable interactions in hollow-core fibers. Based on the Green function formalism of macroscopic quantum electrodynamics, we have recently shown that the existence of a fundamental mode without cut-off [2] implies a far-field contribution to van der Waals interaction between excited atoms, thereby making it possible to observe the yet elusive retarded dispersion potential between two emitters. We show how to extend the fourth-order perturbation theory result [3] to van der Waals potentials at finite temperature and discuss the influence of guided modes on the resonantly enhanced interaction between (highly) excited atoms in a one-dimensional waveguide [4].