1,256 research outputs found
Moving Detectors in Cavities
We consider two-level detectors, coupled to a quantum scalar field, moving
inside cavities. We highlight some pathological resonant effects due to abrupt
boundaries, and decide to describe the cavity by switching smoothly the
interaction by a time-dependent gate-like function. Considering uniformly
accelerated trajectories, we show that some specific choices of non-adiabatic
switching have led to hazardous interpretations about the enhancement of the
Unruh effect in cavities. More specifically, we show that the
emission/absorption ratio takes arbitrary high values according to the emitted
quanta properties and to the transients undergone at the entrance and the exit
of the cavity, {\it independently of the acceleration}. An explicit example is
provided where we show that inertial and uniformly accelerated world-lines can
even lead to the same ``pseudo-temperature''.Comment: 13 pages, 6 figures, version accepted in Phys.Rev.
Stochastic Quantization and Casimir Forces: Pistons of Arbitrary Cross Section
Recently, a method based on stochastic quantization has been proposed to
compute the Casimir force and its fluctuations in arbitrary geometries. It
relies on the spectral decomposition of the Laplacian operator in the given
geometry. Both quantum and thermal fluctuations are considered. Here we use
such method to compute the Casimir force on the plates of a finite piston of
arbitrary cross section. Asymptotic expressions valid at low and high
temperatures and short and long distances are obtained. The case of a piston
with triangular cross section is analysed in detail. The regularization of the
divergent stress tensor is described.Comment: 10 pages and 4 figures. Accepted for publication in the Proceedings
of the tenth conference on Quantum Field Theory under the influence of
external conditions - QFEXT'1
Of Some Theoretical Significance: Implications of Casimir Effects
In his autobiography Casimir barely mentioned the Casimir effect, but
remarked that it is "of some theortical significance." We will describe some
aspects of Casimir effects that appear to be of particular significance now,
more than half a century after Casimir's famous paper
Weak dispersive forces between glass-gold macroscopic surfaces in alcohols
In this work we concentrate on an experimental validation of the Lifshitz
theory for van der Waals and Casimir forces in gold-alcohol-glass systems. From
this theory weak dispersive forces are predicted when the dielectric properties
of the intervening medium become comparable to one of the interacting surfaces.
Using inverse colloid probe atomic force microscopy dispersive forces were
measured occasionally and under controlled conditions by addition of salt to
screen the electrostatic double layer force if present. The dispersive force
was found to be attractive, and an order of magnitude weaker than that in air.
Although the theoretical description of the forces becomes less precise for
these systems even with full knowledge of the dielectric properties, we find
still our results in reasonable agreement with Lifshitz theory.Comment: 19 pages, 7 figure
Lifshitz Interaction between Dielectric Bodies of Arbitrary Geometry
A formulation is developed for the calculation of the
electromagnetic--fluctuation forces for dielectric objects of arbitrary
geometry at small separations, as a perturbative expansion in the dielectric
contrast. The resulting Lifshitz energy automatically takes on the form of a
series expansion of the different many-body contributions. The formulation has
the advantage that the divergent contributions can be readily determined and
subtracted off, and thus makes a convenient scheme for realistic numerical
calculations, which could be useful in designing nano-scale mechanical devices
Invariant tensors and Casimir operators for simple compact Lie groups
The Casimir operators of a Lie algebra are in one-to-one correspondence with
the symmetric invariant tensors of the algebra. There is an infinite family of
Casimir operators whose members are expressible in terms of a number of
primitive Casimirs equal to the rank of the underlying group. A systematic
derivation is presented of a complete set of identities expressing
non-primitive symmetric tensors in terms of primitive tensors. Several examples
are given including an application to an exceptional Lie algebra.Comment: 11 pages, LaTeX, minor changes, version in J. Math. Phy
Evanescent character of the repulsive thermal Casimir force
The physical origin of the negative thermal correction to the Casimir force
between metals is clarified. For this purpose the asymptotic behavior of the
thermal Casimir force is analyzed at large and small distances in the real
frequency representation. Contributions from propagating and evanescent waves
are considered separately. At large distances they cancel each other in
substantial degree so that only the attractive Lifshitz limit survives. At
smaller separations the repulsive evanescent contribution of s-polarization
dominates in the case of two metals or a metal and a high-permittivity
dielectric. Common origin and order of magnitude of the repulsion in these two
cases demonstrate naturalness of the controversial large thermal correction
between metals.Comment: to be published in Phys. Rev.
Measurement of the Temperature Dependence of the Casimir-Polder Force
We report on the first measurement of a temperature dependence of the
Casimir-Polder force. This measurement was obtained by positioning a nearly
pure 87-Rb Bose-Einstein condensate a few microns from a dielectric substrate
and exciting its dipole oscillation. Changes in the collective oscillation
frequency of the magnetically trapped atoms result from spatial variations in
the surface-atom force. In our experiment, the dielectric substrate is heated
up to 605 K, while the surrounding environment is kept near room temperature
(310 K). The effect of the Casimir-Polder force is measured to be nearly 3
times larger for a 605 K substrate than for a room-temperature substrate,
showing a clear temperature dependence in agreement with theory.Comment: 4 pages, 4 figures, published in Physical Review Letter
Modification of energy shifts of atoms by the presence of a boundary in a thermal bath and the Casimir-Polder force
We study the modification by the presence of a plane wall of energy level
shifts of two-level atoms which are in multipolar coupling with quantized
electromagnetic fields in a thermal bath in a formalism which separates the
contributions of thermal fluctuations and radiation reaction and allows a
distinct treatment to atoms in the ground and excited states. The position
dependent energy shifts give rise to an induced force acting on the atoms. We
are able to identify three different regimes where the force shows distinct
features and examine, in all regimes, the behaviors of this force in both the
low temperature limit and the high temperature limit for both the ground state
and excited state atoms, thus providing some physical insights into the
atom-wall interaction at finite temperature. In particular, we show that both
the magnitude and the direction of the force acting on an atom may have a clear
dependence on atomic the polarization directions. In certain cases, a change of
relative ratio of polarizations in different directions may result in a change
of direction of the force.Comment: 29 pages, 3 figure
Development of a high-sensitivity torsion balance to investigate the thermal Casimir force
We report development of a high-sensitivity torsion balance to measure the
thermal Casimir force. Special emphasis is placed on experimental
investigations of a possible surface electric force originating from surface
patch potentials that have been recently noticed by several experimental
groups. By gaining a proper understanding of the actual contribution of the
surface electric force in real materials, we aim to undertake precision force
measurements to resolve the Casimir force at finite temperature in real metals,
as well as in other semiconducting materials, such as graphene.Comment: Proceedings of the 10th International Conference "Quantum Field
Theory Under the Influence of External Conditions"; 11 pages and 4 figure
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