15 research outputs found
New experimental limits on non-Newtonian forces in the micrometer-range
We report measurements of the short-range forces between two macroscopic
gold-coated plates using a torsion pendulum. The force is measured for
separations between 0.7 m and 7 m, and is well described by a
combination of the Casimir force, including the finite-temperature correction,
and an electrostatic force due to patch potentials on the plate surfaces. We
use our data to place constraints on the Yukawa-type "new" forces predicted by
theories with extra dimensions. We establish a new best bound for force ranges
0.4 m to 4 m, and, for forces mediated by gauge bosons propagating in
dimensions and coupling to the baryon number, extract a
-dimensional Planck scale lower limit of TeV.Comment: 4 pages, 2 figure
Measurement of the short-range attractive force between Ge plates using a torsion balance
We have measured the short-range attractive force between crystalline Ge
plates, and found contributions from both the Casimir force and an electrical
force possibly generated by surface patch potentials. Using a model of surface
patch effects that generates an additional force due to a distance dependence
of the apparent contact potential, the electrical force was parameterized using
data at distances where the Casimir force is relatively small. Extrapolating
this model, to provide a correction to the measured force at distances less
than 5 m, shows a residual force that is in agreement, within experimental
uncertainty, with five models that have been used to calculate the Casimir
force.Comment: 5 pages and 4 figures, version
Exact zero-point interaction energy between cylinders
We calculate the exact Casimir interaction energy between two perfectly
conducting, very long, eccentric cylindrical shells using a mode summation
technique. Several limiting cases of the exact formula for the Casimir energy
corresponding to this configuration are studied both analytically and
numerically. These include concentric cylinders, cylinder-plane, and eccentric
cylinders, for small and large separations between the surfaces. For small
separations we recover the proximity approximation, while for large separations
we find a weak logarithmic decay of the Casimir interaction energy, typical of
cylindrical geometries.Comment: 20 pages, 7 figure
On electrostatic and Casimir force measurements between conducting surfaces in a sphere-plane configuration
We report on measurements of forces acting between two conducting surfaces in
a spherical-plane configuration in the 35 nm-1 micrometer separation range. The
measurements are obtained by performing electrostatic calibrations followed by
a residual analysis after subtracting the electrostatic-dependent component. We
find in all runs optimal fitting of the calibrations for exponents smaller than
the one predicted by electrostatics for an ideal sphere-plane geometry. We also
find that the external bias potential necessary to minimize the electrostatic
contribution depends on the sphere-plane distance. In spite of these anomalies,
by implementing a parametrixation-dependent subtraction of the electrostatic
contribution we have found evidence for short-distance attractive forces of
magnitude comparable to the expected Casimir-Lifshitz force. We finally discuss
the relevance of our findings in the more general context of Casimir-Lifshitz
force measurements, with particular regard to the critical issues of the
electrical and geometrical characterization of the involved surfaces.Comment: 22 pages, 15 figure
Casimir energy and geometry : beyond the Proximity Force Approximation
We review the relation between Casimir effect and geometry, emphasizing
deviations from the commonly used Proximity Force Approximation (PFA). We use
to this aim the scattering formalism which is nowadays the best tool available
for accurate and reliable theory-experiment comparisons. We first recall the
main lines of this formalism when the mirrors can be considered to obey
specular reflection. We then discuss the more general case where non planar
mirrors give rise to non-specular reflection with wavevectors and field
polarisations mixed. The general formalism has already been fruitfully used for
evaluating the effect of roughness on the Casimir force as well as the lateral
Casimir force or Casimir torque appearing between corrugated surfaces. In this
short review, we focus our attention on the case of the lateral force which
should make possible in the future an experimental demonstration of the
nontrivial (i.e. beyond PFA) interplay of geometry and Casimir effect.Comment: corrected typos, added references, QFEXT'07 special issue in J. Phys.
Observation of the thermal Casimir force
Quantum theory predicts the existence of the Casimir force between
macroscopic bodies, due to the zero-point energy of electromagnetic field modes
around them. This quantum fluctuation-induced force has been experimentally
observed for metallic and semiconducting bodies, although the measurements to
date have been unable to clearly settle the question of the correct
low-frequency form of the dielectric constant dispersion (the Drude model or
the plasma model) to be used for calculating the Casimir forces. At finite
temperature a thermal Casimir force, due to thermal, rather than quantum,
fluctuations of the electromagnetic field, has been theoretically predicted
long ago. Here we report the experimental observation of the thermal Casimir
force between two gold plates. We measured the attractive force between a flat
and a spherical plate for separations between 0.7 m and 7 m. An
electrostatic force caused by potential patches on the plates' surfaces is
included in the analysis. The experimental results are in excellent agreement
(reduced of 1.04) with the Casimir force calculated using the Drude
model, including the T=300 K thermal force, which dominates over the quantum
fluctuation-induced force at separations greater than 3 m. The plasma
model result is excluded in the measured separation range.Comment: 6 page
Casimir-Polder force between an atom and a dielectric plate: thermodynamics and experiment
The low-temperature behavior of the Casimir-Polder free energy and entropy
for an atom near a dielectric plate are found on the basis of the Lifshitz
theory. The obtained results are shown to be thermodynamically consistent if
the dc conductivity of the plate material is disregarded. With inclusion of dc
conductivity, both the standard Lifshitz theory (for all dielectrics) and its
generalization taking into account screening effects (for a wide range of
dielectrics) violate the Nernst heat theorem. The inclusion of the screening
effects is also shown to be inconsistent with experimental data of Casimir
force measurements. The physical reasons for this inconsistency are elucidated.Comment: 10 pages, 1 figure; improved discussion; to appear in J. Phys. A:
Math. Theor. (Fast Track Communications
Conductivity of dielectric and thermal atom-wall interaction
We compare the experimental data of the first measurement of a temperature
dependence of the Casimir-Polder force by Obrecht et al. [Phys. Rev. Lett. {\bf
98}, 063201 (2007)] with the theory taking into account small, but physically
real, static conductivity of the dielectric substrate. The theory is found to
be inconsistent with the data. The conclusion is drawn that the conductivity of
dielectric materials should not be included in the model of the dielectric
response in the Lifshitz theory. This conclusion obtained from the long
separation measurement is consistent with related but different results
obtained for semiconductors and metals at short separations.Comment: 4 pages, 2 figures; page size is correcte
Low temperature Casimir-Lifshitz free energy and entropy: the case of poor conductors
The controversy concerning the temperature correction to the Casimir force
has been ongoing for almost a decade with no view to a solution and has
recently been extended to include semiconducting materials. We review some
theoretical aspects of formal violations of Nernst's heat theorem in the
context of Casimir Lifshitz thermodynamics and the role of the exponent of the
leading term of the dielectric permittivity with respect to imaginary
frequency. A general formalism for calculating the temperature corrections to
free energy at low temperatures is developed for systems which do not exhibit
such anomalies, and the low temperature behaviour of the free energy in a gap
between half-spaces of poorly conducting materials modelled with a Drude type
permittivity is calculated.Comment: Contributions to Proceedings of "60 Years of Casimir Effect"
Brasilia, June 200
Dynamical Casimir Effect in a Leaky Cavity at Finite Temperature
The phenomenon of particle creation within an almost resonantly vibrating
cavity with losses is investigated for the example of a massless scalar field
at finite temperature. A leaky cavity is designed via the insertion of a
dispersive mirror into a larger ideal cavity (the reservoir). In the case of
parametric resonance the rotating wave approximation allows for the
construction of an effective Hamiltonian. The number of produced particles is
then calculated using response theory as well as a non-perturbative approach.
In addition we study the associated master equation and briefly discuss the
effects of detuning. The exponential growth of the particle numbers and the
strong enhancement at finite temperatures found earlier for ideal cavities turn
out to be essentially preserved. The relevance of the results for experimental
tests of quantum radiation via the dynamical Casimir effect is addressed.
Furthermore the generalization to the electromagnetic field is outlined.Comment: 48 pages, 8 figures typos corrected & references added and update