arXiv subjects

M. S. Tomas

Publications and source records attributed to M. S. Tomas.

7 recordsLinked to original sources

arXiv2006

Medium effects on the van der Waals force

We consider the van der Waals interaction between two ground-state atoms embedded in adjacent semi-infinite magnetodielectric media, with emphasis on medium effects on it. We demonstrate that, in this case, at small atom-atom distances the van der Waals interaction is screened by the surrounding media in the same way as in an effective (single) medium. At larger atomic distances, however, its dependence on the material parameters of the system and the positions of the atoms is more complex. We also calculate the Casimir-Polder potential of an atom A arising from a uniform distribution of atoms B in the medium across the interface. Comparison of this potential with the corresponding result deduced from the Casimir force on a thin composite slab in front of a composite semi-infinite medium, both obeying the Clausius-Mossotti relation, suggests a hint on how to improve a well-known formula for the van der Waals potential with respect to the local-field effects.

quant-ph↗

arXiv2006

Medium-modified Casimir forces

We argue that the results for the vacuum forces on a slab and on an atom embedded in a magnetodielectric medium near a mirror, obtained using a recently suggested Lorentz-force approach to the Casimir effect, are equivalent to the corresponding results obtained in a traditional way. We also derive a general expression for the atom-atom force in a medium and extend a few classical results concerning this force in vacuum and dielectrics to magnetodielectric systems. This, for example, reveals that the (repulsive) interaction between atoms of different polarizability type is at small distances unaffected by a (weakly polarizable) medium.

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arXiv2005

Vacuum force on an atom in a magnetodielectric cavity

We demonstrate that, according to a recently suggested Lorentz-force approach to the Casimir effect, the vacuum force on an atom embedded in a material cavity differs substantially from the force on an atom of the cavity medium. The force on an embedded atom is of the familiar (van der Waals and Casimir-Polder) type, however, more strongly modified by the cavity medium than usually considered. The force on an atom of the cavity medium is of the medium-assisted force type with rather unusual properties, as demonstrated very recently [M. S. Tomas, Phys. Rev. A 71, 060101(R) (2005)]. This implies similar properties of the vacuum force between two atoms in a medium.

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arXiv2005

Casimir force between dispersive magnetodielectrics

We extend our approach to the Casimir effect between absorbing dielectric multilayers [M. S. Tomas, Phys. Rev. A 66, 052103 (2002)] to magnetodielectric systems. The resulting expression for the force is used to numerically explore the effect of the medium dispersion on the attractive/repulsive force in a metal-magnetodielectric system described by the Drude-Lorentz permittivities and permeabilities.

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arXiv2005

Medium-assisted vacuum force

We discuss some implications of a very recently obtained result for the force on a slab in a planar cavity based on the calculation of the vacuum Lorentz force [C. Raabe and D.-G. Welsch, Phys. Rev. A 71, 013814 (2005)]. We demonstrate that, according to this formula, the total force on the slab consists of a medium-screened Casimir force and, in addition to it, a medium-assisted force. The sign of of the medium-assisted force is determined solely by the properties of the cavity mirrors. In the Lifshitz configuration, this force is proportional to 1/d at small distances and is very small compared with the corresponding van der Waals force. At large distances, however, it is proportional to 1/d^4 and is comparable with the Casimir force, especially for denser media. The exponents in these power laws decrease by 1 in the case of a thin slab. The formula for the medium-assisted force also describes the force on a layer of the cavity medium, which has similar properties. For dilute media, it implies an atom-mirror interaction of the Coulomb type at small and of the Casimir-Polder type at large atom-mirror distances. For a perfectly reflecting mirror, the latter force is effectively only three-times smaller than the Casimir-Polder force.

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arXiv2005

Screened Casimir forces

We demonstrate that a very recently obtained formula for the force on a slab in a material planar cavity based on the calculation of the vacuum Lorentz force [C. Raabe and D.-G. Welsch, Phys. Rev. A 71, 013814 (2005)] describes a (medium) screened Casimir force and, in addition to it, a medium-assisted force. The latter force also describes the force on the cavity medium. For dilute media, it implies the atom-mirror interaction of the Casimir-Polder type at large and of the Coulomb type at small atom-mirror distances of which the sign is insensitive to the polarizability type (electric or magnetic) of the atom.

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arXiv2002

Casimir force in absorbing multilayers

The Casimir effect in a dispersive and absorbing multilayered system is considered adopting the (net) vacuum-field pressure point of view to the Casimir force. Using the properties of the macroscopic field operators appropriate for absorbing systems and a convenient compact form of the Green function for a multilayer, a straightforward and transparent derivation of the Casimir force in a lossless layer of an otherwise absorbing multilayer is presented. The resulting expression in terms of the reflection coefficients of the surrounding stacks of layers is of the same form as that obtained by Zhou and Spruch for a purely dispersive multilayer using the (surface) mode summation method [Phys. Rev. A {\bf 52}, 297 (1995)]. Owing to the recursion relations which the generalized Fresnel coefficients satisfy, this result can be applied to more complex systems with planar symmetry. This is illustrated by calculating the Casimir force on a dielectric (metallic) slab in a planar cavity with realistic mirrors. Also, a relationship between the Casimir force and energy in two different layers is established.

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