Three-body effects in Casimir-Polder repulsion

Milton, Kimball A.; Abalo, E. K.; Parashar, Prachi; Pourtolami, Nima; Brevik, Iver; Ellingsen, Simen Å.; Buhmann, Stefan Yoshi; Scheel, Stefan

doi:10.1103/physreva.91.042510

Cited by 19 publications

(20 citation statements)

References 47 publications

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“…Moreover, the sign of the dispersion force can be reversed. A repulsive force with associated equilibrium, at least in the form of a saddle point, has been predicted for objects above a metal plate with a circular hole [11][12][13][14] and near wedges [15]. Apart from geometry, non-equilibrium situations such as resonant Casimir-Polder interactions of excited atoms can provide transient repulsion [16,17].…”

Section: Introductionmentioning

confidence: 99%

Impact of anisotropy on the interaction of an atom with a one-dimensional nano-grating

Buhmann

Marachevsky

Scheel

2016

Int. J. Mod. Phys. A

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We study the interaction of an atom with a one-dimensional nanograting within the framework of macroscopic QED, with special emphasis on possible anisotropic contributions. To this end, we first derive the scattering Green's tensor of the grating by means of a Rayleigh expansion and discuss its symmetry properties and asymptotes. We then determine the Casimir-Polder potential of an atom with the grating. In particular, we find that strong anisotropy can lead to a repulsive Casimir-Polder potential in the normal direction.

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Section: Introductionmentioning

confidence: 99%

Impact of anisotropy on the interaction of an atom with a one-dimensional nano-grating

Buhmann

Marachevsky

Scheel

2016

Int. J. Mod. Phys. A

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“…Finally, we remark that negative entropy is not unrelated to Casimir repulsion (see, for example, Ref. [21]). In both cases what is involved is nonmonotonicity in the quantum free energy.…”

Section: Discussionmentioning

confidence: 77%

Negative entropies in Casimir and Casimir‐Polder interactions

Milton

Kalauni

et al. 2016

Fortschritte der Physik

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It has been increasingly becoming clear that Casimirand Casimir-Polder entropies may be negative in certain regions of temperature and separation. In fact, the occurrence of negative entropy seems to be a nearly ubiquitous phenomenon. This is most highlighted in the quantum vacuum interaction of a nanoparticle with a conducting plate or between two nanoparticles. It has been argued that this phenomenon does not violate physical intuition, since the total entropy, including the self-entropies of the plate and the nanoparticle, should be positive. New calculations, in fact, seem to bear this out at least in certain cases. The thermal Casimir puzzleFor 15 years there has been a controversy surrounding entropy in the Casimir effect. This is most famously centered around the issue of how to describe a real metal, in particular, the permittivity ε(ω) at zero frequency [1]. The latter determines the low-temperature and high temperature corrections to the free energy, and hence to the entropy. The issue involves how ω 2 ε(ω) behaves as ω → 0.Dissipation or finite conductivity implies this vanishes; this leads to a linear temperature dependence at low temperature, and a reduction of the high-temperature force. Most experiments [2-4], but not all [5], favor the nondissipative plasma model! For an overview of the status of both theory and experiment, see Ref.[6].The Drude model, and general thermodynamic and electrodynamic arguments, suggest that the transverse electric (TE) reflection coefficient at zero frequency for a good, but imperfect, metal plate should vanish. Careful calculations for lossy parallel plates show that at very low temperature the free energy approaches a constant quadratically in the temperature, thus forcing the entropy to vanish at zero temperature [7]. Thus, there is no violation of the third law of thermodynamics. However, there would persist a region at low temperature in which the entropy would be negative. This was not thought to be a problem, since the interaction Casimir free energy does not describe the entire system of the Casimir apparatus, whose total entropy must necessarily be positive. The physical basis for the negative entropy region remains somewhat mysterious. Here we address negative entropy arising from geometry. The interplay of geometry and material properties is further explored in Ref. [8].For some time it has been known that negative entropy regions can emerge geometrically. For example, when a perfectly conducting sphere is near a perfectly conducting plate, the entropy at room temperature can turn negative, with enhancement of the effect occurring for smaller spheres [9]. The occurrence of negative interaction entropies for a small sphere in front of a plane or another sphere is illustrated in Fig. 1 within the dipole and single-scattering approximation. Since the negative entropy region is enhanced by making the sphere small, this suggests that the phenomena be explored by considering the dipole approximation only. That is, we will examine point particles, atoms or nanopa...

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“…Repulsive Casimir forces are of practical interest, for example, in the field of nanomachines [12], for which Casimir-related effects are the ultimate source of friction. See [13] for a detailed review.…”

Section: Introductionmentioning

confidence: 99%

Casimir forces on atoms in optical cavities

2014

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Casimir-type forces, such as those between two neutral conducting plates, or between a sphere, atom or molecule and a plate have been widely studied and are becoming of increasing significance, for example, in nanotechnology. A key challenge is to better understand, from a fundamental microscopic approach, why the Casimir force is in some circumstances attractive and in others repulsive. Here, we study the Casimir-Polder forces experienced by small quantum systems such as atoms or molecules in an optical cavity. In order to make the problem more tractable, we work in a 1+1 dimensional setting, we take into account only the ground state and first excited state of the atom and we model the electromagnetic field as a scalar field with Dirichlet or Neumann boundary conditions. This allows us to determine the conditions for the Casimir force to be attractive or repulsive for individual atoms, namely through the interplay of paramagnetic and diamagnetic vacuum effects. We also study the microscopic-macroscopic transition, finding that as the number of atoms in the cavity is increased, the atoms start to affect the Casimir force exerted on the cavity walls similarly to a dielectric medium.

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Three-body effects in Casimir-Polder repulsion

Cited by 19 publications

References 47 publications

Impact of anisotropy on the interaction of an atom with a one-dimensional nano-grating

Impact of anisotropy on the interaction of an atom with a one-dimensional nano-grating

Negative entropies in Casimir and Casimir‐Polder interactions

Casimir forces on atoms in optical cavities

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