111 research outputs found
Hide it to see it better: a robust setup to probe the thermal Casimir effect
We describe a Casimir setup consisting of two aligned sinusoidally corrugated
Ni surfaces, one of which is "hidden" by a thin opaque layer of gold with a
flat exposed surface. The gold layer acts as a low-pass filter that allows for
a clean observation of the controversial thermal Casimir force between the
corrugations, with currently available Casimir apparatuses. The proposed scheme
of measurement, based on the phase-dependent modulation of the Casimir force,
requires no electrostatic calibrations of the apparatus, and is unaffected by
uncertainties in the knowledge of the optical properties of the surfaces. This
scheme should allow for an unambiguous discrimination between alternative
theoretical prescriptions that have been proposed in the literature for the
thermal Casimir effect.Comment: 5 pages, 2 encapsulated figures, final version accepted for
publication in Physical Review Letter
Exact Casimir interaction of perfectly conducting three-spheres in four euclidean dimensions
Exploiting conformal symmetry, we derive a simple exact formula for the
classical electromagnetic Casimir interaction of two perfectly conducting
three-spheres, including the sphere-plate geometry as a special case, in four
euclidean dimensions. We verify that the short distance expansion of the
Casimir energy agrees to leading order with the Proximity Force Approximation
(PFA), while the next-to-leading-order is in agreement with a recently proposed
derivative expansion of the Casimir energy. At the next-to-next-to-leading
order we find a non-analytic correction to PFA, which for a sphere-plate system
is of the order of , where is the separation and
the sphere radius.Comment: 19 pages, 2 figure
Observing the Casimir-Lifshitz Force Out of Thermal Equilibrium
The thermal Casimir-Lifshitz force among two bodies held at different
temperatures displays striking features that are absent in systems in thermal
equilibrium. The manifestation of this force has been observed so far only in
Bose-Einstein condensates close to a heated substrate, but never between two
macroscopic bodies. Observation of the thermal Casimir-Lifhitz force out of
thermal equilibrium with conventional Casimir setups is very difficult, because
for experimentally accessible separations the thermal force is small compared
to the zero-temperature quantum Casimir force, unless prohibitively large
temperature differences among the plates are considered. We describe an
apparatus that allows for a direct observation of the thermal force out of
equilibrium for submicron separations and for moderate temperature differences
between the plates.Comment: 5 pages, 3 encapsulated figure
Comment on " Low-frequency character of the Casimir force between metallic films"
In Phys. Rev. {\bf E 70}, 047102 (2004), J.R. Torgerson and S.K. Lamoreaux
investigated for the first time the real-frequency spectrum of finite
temperature correction to the Casimir force, for metallic plates of finite
conductivity. The very interesting result of this study is that the correction
from the TE mode is dominated by low frequencies, for which the dielectric
description of the metal is invalid. However, their analysis of the problem,
based on more appropriate low-frequency metallic boundary conditions, uses an
incorrect form of boundary conditions for TE modes. We repeat their analysis,
using the correct boundary conditions. Our computations confirm their most
important result: contrary to the result of the dielectric model, the thermal
TE mode correction leads to an increase in the TE mode force of attraction
between the plates. The magnitude of the correction has a value about twenty
times larger than that quoted by them.Comment: 3 pages, 2 figures. In press on Phys. Rev.
Apparatus to probe the influence on the Casimir effect of the Mott-Anderson metal-insulator transition in doped semiconductors
We describe an isoelectronic differential apparatus designed to observe the
influence on the Casimir force of the Mott-Anderson metal-insulator transition
in doped semiconductors. Alternative theories of dispersion forces lead to
different predictions for this effect. The investigation of this problem by
standard apparatus, based on absolute measurements of the Casimir force, is
very difficult because the effect is small in the region of sub-micron
separations, where the Casimir force can be measured precisely. The
differential apparatus described here is immune by design to several sources of
error that blur the interpretation of Casimir experiments, like electrostatic
patches, inaccurate determination of plates separation, surface roughness and
errors in the optical data. With the help of the proposed setup it should be
possible to establish conclusively which among the alternative theories of the
Casimir effect for semiconducting test bodies is correct.Comment: 14 pages, 9 figures, accepted for publication in Phys. Rev.
Wave-scattering from a gently curved surface
We study wave scattering from a gently curved surface. We show that the
recursive relations, implied by shift invariance, among the coefficients of the
perturbative series for the scattering amplitude allow to perform an infinite
resummation of the perturbative series to all orders in the amplitude of the
corrugation. The resummed series provides a derivative expansion of the
scattering amplitude in powers of derivatives of the height profile, which is
expected to become exact in the limit of quasi-specular scattering. We discuss
the relation of our results with the so-called small-slope approximation
introduced some time ago by Voronovich.Comment: 5 pages, accepted for publication in Phys. Lett.
Classical brackets for dissipative systems
We show how to write a set of brackets for the Langevin equation, describing
the dissipative motion of a classical particle, subject to external random
forces. The method does not rely on an action principle, and is based solely on
the phenomenological description of the dissipative dynamics as given by the
Langevin equation. The general expression for the brackets satisfied by the
coordinates, as well as by the external random forces, at different times, is
determined, and it turns out that they all satisfy the Jacobi identity. Upon
quantization, these classical brackets are found to coincide with the
commutation rules for the quantum Langevin equation, that have been obtained in
the past, by appealing to microscopic conservative quantum models for the
friction mechanism.Comment: Latex file, 8 pages, prepared for the Conference Spacetime and
Fundamental Interactions: Quantum Aspects, Vietri sul Mare, Italy, 26-31 May
200
New classical brackets for dissipative systems
A set of brackets for classical dissipative systems, subject to external
random forces, are derived. The method is inspired to the old procedure found
by Peierls, for deriving the canonical brackets of conservative systems,
starting from an action principle. It is found that an adaptation of Peierls'
method is applicable also to dissipative systems, when the friction term can be
described by a linear functional of the coordinates, as is the case in the
classical Langevin equation, with an arbitrary memory function. The general
expression for the brackets satisfied by the coordinates, as well as by the
external random forces, at different times, is determined, and it turns out
that they all satisfy the Jacobi identity. Upon quantization, these classical
brackets are found to coincide with the commutation rules for the quantum
Langevin equation, that have been obtained in the past, by appealing to
microscopic conservative quantum models for the friction mechanism.Comment: 4 page
Casimir--Polder force between anisotropic nanoparticles and gently curved surfaces
The Casimir--Polder interaction between an anisotropic particle and a surface
is orientation dependent. We study novel orientational effects that arise due
to curvature of the surface for distances much smaller than the radii of
curvature by employing a derivative expansion. For nanoparticles we derive a
general short distance expansion of the interaction potential in terms of their
dipolar polarizabilities. Explicit results are presented for nano-spheroids
made of SiO and gold, both at zero and at finite temperatures. The
preferred orientation of the particle is strongly dependent on curvature,
temperature, as well as material properties.Comment: 9 pages, 10 encapsulated figure
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