Dispersion forces: analysis of local-field effects and inclusion of excitation

In this thesis, we have used macroscopic quantum electrodynamics to extend the concept of dispersion forces to objects in media and on excited systems.Our results facilitate a deeper understanding of dispersion interactions in the context of biological systems and colloid science.They stress the potential of amplification and left-handed metamaterials for manipulating dispersion forces on atoms and bodies in nanotechnologies.We have first studied the Casimir-Polder potential of ground-state atom in front of a planar interface between two magnetodielectric media where the local-field correction is implemented via the Onsager real-cavity model.In particular, we have proposed an estimate of the on-surface value of the potential.Secondly, we have examined the Casimir-Polder interaction of a ground-state atom and a small magnetodielectric sphere in the presence of arbitrary magnetodielectric background media and bodies. We have proposed a model that is able to describe molecular systems of arbitrary size.To demonstrate the impact of negative refraction on the Casimir-Polder potential and the spontaneous decay rate of an excited atom, we have studied a superlens scenario.We have shown that an arbitrarily small but finite amount of material absorption drastically changes the Casimir-Polder potential and the decay rate compared to the ideal scenario with vanishing absorption.We have further calculated the Casimir force on an amplifying but linearly responding, magnetoelectric body. As we have shown, amplification leads to resonant force components which can be exploited to create repulsive Casimir forces. Finally, we have proven that the Casimir force on an optically dilute amplifying body can be calculated as a sum over the Casimir-Polder forces on the excited atoms inside the body

Impact of amplifying media on the Casimir force

On the basis of macroscopic quantum electrodynamics, a theory of Casimir forces in the presence of on linearly amplifying bodies is presented which provides a consistent framework for studying the effect of, e.g., amplifying left-handed metamaterials on dispersion forces. A general formula for the Casimir force acting on an amplifying body is derived. It is shown that the force can be given in terms of the classical Green tensor and that it can be decomposed into a resonant component associated with emission processes and an off-resonant Lifshitz-type component looking formally the same as for a purely absorbing body. It is explicitly demonstrated that the result generalizes microscopic approaches beyond the perturbative domain: In the dilute-gas limit, the force acting on an amplifying body reduces to a sum over the Casimir--Polder forces acting on the excited body atoms.Comment: 5 pages, extension

Van der Waals interaction and spontaneous decay of an excited atom in a superlens-type geometry

Within the framework of macroscopic quantum electrodynamics, the resonant van der Waals potential experienced by an excited two-level atom near a planar magneto-electric two-layer system consisting of a slab of left-handed material and a perfect mirror is studied. It is shown that disregarding of material absorption leads to unphysical results, with divergent values for the potential away from the surface. Under appropriate conditions, the setup is found to feature a barrier near the surface which can be employed to levitate particles or used as a trapping or cooling mechanism. Finally, the problem of spontaneous decay [J. K\"{a}stel and M. Fleischhauer, Phys. Rev. A \textbf{68}, 011804(R) (2005)] is revisited. Disregarding of absorption is shown to drastically falsify the dependence on the atomic position of the decay rate.Comment: 10 Pages, 6 figure

Local-field correction to one- and two-atom van der Waals interactions

Based on macroscopic quantum electrodynamics in linearly and causally responding media, we study the local-field corrected van der Waals potentials and forces for unpolarized ground-state atoms placed within a magnetoelectric medium of arbitrary size and shape. We start from general expressions for the van der Waals potentials in terms of the (classical) Green tensor of the electromagnetic field and the atomic polarizability and incorporate the local-field correction by means of the real-cavity model. In this context, special emphasis is given to the decomposition of the Green tensor into a medium part multiplied by a global local-field correction factor and, in the single-atom case, a part that only depends on the cavity characteristics. The result is used to derive general formulas for the local-field corrected van der Waals potentials and forces. As an application, we calculate the van der Waals potential between two ground-state atoms placed within magnetoelectric bulk material.Comment: 9 pages, 2 figures, corrections according to erratu

Casimir-Polder interaction between an atom and a small magnetodielectric sphere

On the basis of macroscopic quantum electrodynamics and point-scattering techniques, we derive a closed expression for the Casimir-Polder force between a ground-state atom and a small magnetodielectric sphere in an arbitrary environment. In order to allow for the presence of both bodies and media, local-field corrections are taken into account. Our results are compared with the known van der Waals force between two ground-state atoms. To continuously interpolate between the two extreme cases of a single atom and a macroscopic sphere, we also derive the force between an atom and a sphere of variable radius that is embedded in an Onsager local-field cavity. Numerical examples illustrate the theory.Comment: 9 pages, 4 figures, minor addition

Local-field corrected van der Waals potentials in magnetodielectric multilayer systems

Within the framework of macroscopic quantum electrodynamics in linear, causal media, we study the van der Waals potentials of ground-state atoms in planar magnetodielectric host media. Our investigation extends earlier ones in two aspects: It allows for the atom to be embedded in a medium, thus covers many more realistic systems; and it takes account of the local-field correction. Two- and three-layer configurations are treated in detail both analytically and numerically. It is shown that an interplay of electric and magnetic properties in neighbouring media may give rise to potential wells or walls. Local-field corrections as high as 80% are found. By calculating the full potential including the translationally invariant and variant parts, we propose a way to estimate the (finite) value of the dispersion potential at the surface between two media. Connection with earlier work intended for biological applications is established.Comment: 12 pages, 5 figure