1,249 research outputs found
Alternative derivation of the Feigel effect and call for its experimental verification
A recent theory by Feigel [Phys. Rev. Lett. {\bf 92}, 020404 (2004)] predicts
the finite transfer of momentum from the quantum vacuum to a fluid placed in
strong perpendicular electric and magnetic fields. The momentum transfer arises
because of the optically anisotropic magnetoelectric response induced in the
fluid by the fields. After summarising Feigel's original assumptions and
derivation (corrected of trivial mistakes), we rederive the same result by a
simpler route, validating Feigel's semi-classical approach. We then derive the
stress exerted by the vacuum on the fluid which, if the Feigel hypothesis is
correct, should induce a Poiseuille flow in a tube with maximum speed m/s (2000 times larger than Feigel's original prediction). An experiment
is suggested to test this prediction for an organometallic fluid in a tube
passing through the bore of a high strength magnet. The predicted flow can be
measured directly by tracking microscopy or indirectly by measuring the flow
rate (ml/min) corresponding to the Poiseuille flow. A second
experiment is also proposed whereby a `vacuum radiometer' is used to test a
recent prediction that the net force on a magnetoelectric slab in the vacuum
should be zero.Comment: 20 pages, 1 figures. revised and improved versio
Quantum radiation in external background fields
A canonical formalism is presented which allows for investigations of quantum
radiation induced by localized, smooth disturbances of classical background
fields by means of a perturbation theory approach. For massless,
non-selfinteracting quantum fields at zero temperature we demonstrate that the
low-energy part of the spectrum of created particles exhibits a non-thermal
character. Applied to QED in varying dielectrics the response theory approach
facilitates to study two distinct processes contributing to the production of
photons: the squeezing effect due to space-time varying properties of the
medium and of the velocity effect due to its motion. The generalization of this
approach to finite temperatures as well as the relation to sonoluminescence is
indicated.Comment: 20 page
Prime decomposition and correlation measure of finite quantum systems
Under the name prime decomposition (pd), a unique decomposition of an
arbitrary -dimensional density matrix into a sum of seperable density
matrices with dimensions given by the coprime factors of is introduced. For
a class of density matrices a complete tensor product factorization is
achieved. The construction is based on the Chinese Remainder Theorem and the
projective unitary representation of by the discrete Heisenberg group
. The pd isomorphism is unitarily implemented and it is shown to be
coassociative and to act on as comultiplication. Density matrices with
complete pd are interpreted as grouplike elements of . To quantify the
distance of from its pd a trace-norm correlation index is
introduced and its invariance groups are determined.Comment: 9 pages LaTeX. Revised version: changes in the terminology, updates
in ref
Theory of quantum radiation observed as sonoluminescence
Sonoluminescence is explained in terms of quantum radiation by moving
interfaces between media of different polarizability. In a stationary
dielectric the zero-point fluctuations of the electromagnetic field excite
virtual two-photon states which become real under perturbation due to motion of
the dielectric. The sonoluminescent bubble is modelled as an optically empty
cavity in a homogeneous dielectric. The problem of the photon emission by a
cavity of time-dependent radius is handled in a Hamiltonian formalism which is
dealt with perturbatively up to first order in the velocity of the bubble
surface over the speed of light. A parameter-dependence of the zero-order
Hamiltonian in addition to the first-order perturbation calls for a new
perturbative method combining standard perturbation theory with an adiabatic
approximation. In this way the transition amplitude from the vacuum into a
two-photon state is obtained, and expressions for the single-photon spectrum
and the total energy radiated during one flash are given both in full and in
the short-wavelengths approximation when the bubble is larger than the
wavelengths of the emitted light. It is shown analytically that the spectral
density has the same frequency-dependence as black-body radiation; this is
purely an effect of correlated quantum fluctuations at zero temperature. The
present theory clarifies a number of hitherto unsolved problems and suggests
explanations for several more. Possible experiments that discriminate this from
other theories of sonoluminescence are proposed.Comment: Latex file, 28 pages, postscript file with 3 figs. attache
Casimir Energy for a Spherical Cavity in a Dielectric: Applications to Sonoluminescence
In the final few years of his life, Julian Schwinger proposed that the
``dynamical Casimir effect'' might provide the driving force behind the
puzzling phenomenon of sonoluminescence. Motivated by that exciting suggestion,
we have computed the static Casimir energy of a spherical cavity in an
otherwise uniform material. As expected the result is divergent; yet a
plausible finite answer is extracted, in the leading uniform asymptotic
approximation. This result agrees with that found using zeta-function
regularization. Numerically, we find far too small an energy to account for the
large burst of photons seen in sonoluminescence. If the divergent result is
retained, it is of the wrong sign to drive the effect. Dispersion does not
resolve this contradiction. In the static approximation, the Fresnel drag term
is zero; on the mother hand, electrostriction could be comparable to the
Casimir term. It is argued that this adiabatic approximation to the dynamical
Casimir effect should be quite accurate.Comment: 23 pages, no figures, REVTe
Quantum radiation in a plane cavity with moving mirrors
We consider the electromagnetic vacuum field inside a perfect plane cavity
with moving mirrors, in the nonrelativistic approximation. We show that low
frequency photons are generated in pairs that satisfy simple properties
associated to the plane geometry. We calculate the photon generation rates for
each polarization as functions of the mechanical frequency by two independent
methods: on one hand from the analysis of the boundary conditions for moving
mirrors and with the aid of Green functions; and on the other hand by an
effective Hamiltonian approach. The angular and frequency spectra are discrete,
and emission rates for each allowed angular direction are obtained. We discuss
the dependence of the generation rates on the cavity length and show that the
effect is enhanced for short cavity lengths. We also compute the dissipative
force on the moving mirrors and show that it is related to the total radiated
energy as predicted by energy conservation.Comment: 17 pages, 1 figure, published in Physical Review
Dynamical Casimir effect without boundary conditions
The moving-mirror problem is microscopically formulated without invoking the
external boundary conditions. The moving mirrors are described by the quantized
matter field interacting with the photon field, forming dynamical cavity
polaritons: photons in the cavity are dressed by electrons in the moving
mirrors. The effective Hamiltonian for the polariton is derived, and
corrections to the results based on the external boundary conditions are
discussed.Comment: 12 pages, 2 figure
Identity of the van der Waals Force and the Casimir Effect and the Irrelevance of these Phenomena to Sonoluminescence
We show that the Casimir, or zero-point, energy of a dilute dielectric ball,
or of a spherical bubble in a dielectric medium, coincides with the sum of the
van der Waals energies between the molecules that make up the medium. That
energy, which is finite and repulsive when self-energy and surface effects are
removed, may be unambiguously calculated by either dimensional continuation or
by zeta function regularization. This physical interpretation of the Casimir
energy seems unambiguous evidence that the bulk self-energy cannot be relevant
to sonoluminescence.Comment: 7 pages, no figures, REVTe
Observability of the Bulk Casimir Effect: Can the Dynamical Casimir Effect be Relevant to Sonoluminescence?
The experimental observation of intense light emission by acoustically
driven, periodically collapsing bubbles of air in water (sonoluminescence) has
yet to receive an adequate explanation. One of the most intriguing ideas is
that the conversion of acoustic energy into photons occurs quantum
mechanically, through a dynamical version of the Casimir effect. We have argued
elsewhere that in the adiabatic approximation, which should be reliable here,
Casimir or zero-point energies cannot possibly be large enough to be relevant.
(About 10 MeV of energy is released per collapse.) However, there are
sufficient subtleties involved that others have come to opposite conclusions.
In particular, it has been suggested that bulk energy, that is, simply the
naive sum of , which is proportional to the volume, could
be relevant. We show that this cannot be the case, based on general principles
as well as specific calculations. In the process we further illuminate some of
the divergence difficulties that plague Casimir calculations, with an example
relevant to the bag model of hadrons.Comment: 13 pages, REVTe
Direct mode summation for the Casimir energy of a solid ball
The Casimir energy of a solid ball placed in an infinite medium is calculated
by a direct frequency summation using the contour integration. It is assumed
that the permittivity and permeability of the ball and medium satisfy the
condition . Upon deriving the general
expression for the Casimir energy, a dilute compact ball is considered
. In this case the
calculations are carried out which are of the first order in and take
account of the five terms in the Debye expansion of the Bessel functions
involved. The implication of the obtained results to the attempts of explaining
the sonoluminescence via the Casimir effect is shortly discussed.Comment: REVTeX, 7 pages, no figures and tables, treatment of a dilute
dielectric ball is revised, new references are adde
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