1,873 research outputs found
Sonoluminescence: Bogolubov coefficients for the QED vacuum of a time-dependent dielectric bubble
We extend Schwinger's ideas regarding sonoluminescence by explicitly
calculating the Bogolubov coefficients relating the QED vacuum states
associated with changes in a dielectric bubble. Sudden (non-adiabatic) changes
in the refractive index lead to an efficient production of real photons with a
broadband spectrum, and a high-frequency cutoff that arises from the asymptotic
behaviour of the dielectric constant.Comment: 4 pages, RevTeX, 2 figures (.eps file) included with graphics.sty.
Major revisions: physical scenario clarified, additional numerical estimate
Relativistic, Causal Description of Quantum Entanglement and Gravity
A possible solution to the problem of providing a spacetime description of
the transmission of signals for quantum entangled states is obtained by using a
bimetric spacetime structure, in which quantum entanglement measurements alter
the structure of the classical relativity spacetime. A bimetric gravity theory
locally has two lightcones, one which describes classical special relativity
and a larger lightcone which allows light signals to communicate quantum
information between entangled states, after a measurement device detects one of
the entangled states. The theory would remove the tension that exists between
macroscopic classical, local gravity and macroscopic nonlocal quantum
mechanics.Comment: 12 pages. LaTex file. 1 figure. Additional text. To be published in
Int. J. Mod. Phys.
Sonoluminescence as a QED vacuum effect. II: Finite Volume Effects
In a companion paper [quant-ph/9904013] we have investigated several
variations of Schwinger's proposed mechanism for sonoluminescence. We
demonstrated that any realistic version of Schwinger's mechanism must depend on
extremely rapid (femtosecond) changes in refractive index, and discussed ways
in which this might be physically plausible. To keep that discussion tractable,
the technical computations in that paper were limited to the case of a
homogeneous dielectric medium. In this paper we investigate the additional
complications introduced by finite-volume effects. The basic physical scenario
remains the same, but we now deal with finite spherical bubbles, and so must
decompose the electromagnetic field into Spherical Harmonics and Bessel
functions. We demonstrate how to set up the formalism for calculating Bogolubov
coefficients in the sudden approximation, and show that we qualitatively retain
the results previously obtained using the homogeneous-dielectric (infinite
volume) approximation.Comment: 23 pages, LaTeX 209, ReV-TeX 3.2, five figure
A method to measure vacuum birefringence at FCC-ee
It is well-known that the Heisenberg-Euler-Schwinger effective Lagrangian
predicts that a vacuum with a strong static electromagnetic field turns
birefringent. We propose a scheme that can be implemented at the planned
FCC-ee, to measure the nonlinear effect of vacuum birefringence in
electrodynamics arising from QED corrections. Our scheme employs a pulsed laser
to create Compton backscattered photons off a high energy electron beam, with
the FCC-ee as a particularly interesting example. These photons will pass
through a strong static magnetic field, which changes the state of polarization
of the radiation - an effect proportional to the photon energy. This change
will be measured by the use of an aligned single-crystal, where a large
difference in the pair production cross-sections can be achieved. In the
proposed experimental setup the birefringence effect gives rise to a difference
in the number of pairs created in the analyzing crystal, stemming from the fact
that the initial laser light has a varying state of polarization, achieved with
a rotating quarter wave plate. Evidence for the vacuum birefringent effect will
be seen as a distinct peak in the Fourier transform spectrum of the
pair-production rate signal. This tell-tale signal can be significantly above
background with only few hours of measurement, in particular at high energies.Comment: Presented by UIU at the International Symposium on "New Horizons in
Fundamental Physics: From Neutrons Nuclei via Superheavy Elements and
Supercritical Fields to Neutron Stars and Cosmic Rays," held to honor Walter
Greiner on his 80th birthday at Makutsi Safari Farm, South Africa, November
23-29, 201
Unitary equivalence between ordinary intelligent states and generalized intelligent states
Ordinary intelligent states (OIS) hold equality in the Heisenberg uncertainty
relation involving two noncommuting observables {A, B}, whereas generalized
intelligent states (GIS) do so in the more generalized uncertainty relation,
the Schrodinger-Robertson inequality. In general, OISs form a subset of GISs.
However, if there exists a unitary evolution U that transforms the operators
{A, B} to a new pair of operators in a rotation form, it is shown that an
arbitrary GIS can be generated by applying the rotation operator U to a certain
OIS. In this sense, the set of OISs is unitarily equivalent to the set of GISs.
It is the case, for example, with the su(2) and the su(1,1) algebra that have
been extensively studied particularly in quantum optics. When these algebras
are represented by two bosonic operators (nondegenerate case), or by a single
bosonic operator (degenerate case), the rotation, or pseudo-rotation, operator
U corresponds to phase shift, beam splitting, or parametric amplification,
depending on two observables {A, B}.Comment: published version, 4 page
Unitary equivalence between ordinary intelligent states and generalized intelligent states
Ordinary intelligent states (OIS) hold equality in the Heisenberg uncertainty
relation involving two noncommuting observables {A, B}, whereas generalized
intelligent states (GIS) do so in the more generalized uncertainty relation,
the Schrodinger-Robertson inequality. In general, OISs form a subset of GISs.
However, if there exists a unitary evolution U that transforms the operators
{A, B} to a new pair of operators in a rotation form, it is shown that an
arbitrary GIS can be generated by applying the rotation operator U to a certain
OIS. In this sense, the set of OISs is unitarily equivalent to the set of GISs.
It is the case, for example, with the su(2) and the su(1,1) algebra that have
been extensively studied particularly in quantum optics. When these algebras
are represented by two bosonic operators (nondegenerate case), or by a single
bosonic operator (degenerate case), the rotation, or pseudo-rotation, operator
U corresponds to phase shift, beam splitting, or parametric amplification,
depending on two observables {A, B}.Comment: published version, 4 page
Sonoluminescence as a QED vacuum effect: Probing Schwinger's proposal
Several years ago Schwinger proposed a physical mechanism for
sonoluminescence in terms of photon production due to changes in the properties
of the quantum-electrodynamic (QED) vacuum arising from a collapsing dielectric
bubble. This mechanism can be re-phrased in terms of the Casimir effect and has
recently been the subject of considerable controversy. The present paper probes
Schwinger's suggestion in detail: Using the sudden approximation we calculate
Bogolubov coefficients relating the QED vacuum in the presence of the expanded
bubble to that in the presence of the collapsed bubble. In this way we derive
an estimate for the spectrum and total energy emitted. We verify that in the
sudden approximation there is an efficient production of photons, and further
that the main contribution to this dynamic Casimir effect comes from a volume
term, as per Schwinger's original calculation. However, we also demonstrate
that the timescales required to implement Schwinger's original suggestion are
not physically relevant to sonoluminescence. Although Schwinger was correct in
his assertion that changes in the zero-point energy lead to photon production,
nevertheless his original model is not appropriate for sonoluminescence. In
other works (see quant-ph/9805023, quant-ph/9904013, quant-ph/9904018,
quant-ph/9905034) we have developed a variant of Schwinger's model that is
compatible with the physically required timescales.Comment: 18 pages, ReV_TeX 3.2, 9 figures. Major revisions: This document is
now limited to providing a probe of Schwinger's original suggestion for
sonoluminescence. For details on our own variant of Schwinger's ideas see
quant-ph/9805023, quant-ph/9904013, quant-ph/9904018, quant-ph/990503
Schwinger, Pegg and Barnett approaches and a relationship between angular and Cartesian quantum descriptions II: Phase Spaces
Following the discussion -- in state space language -- presented in a
preceding paper, we work on the passage from the phase space description of a
degree of freedom described by a finite number of states (without classical
counterpart) to one described by an infinite (and continuously labeled) number
of states. With that it is possible to relate an original Schwinger idea to the
Pegg and Barnett approach to the phase problem. In phase space language, this
discussion shows that one can obtain the Weyl-Wigner formalism, for both
Cartesian {\em and} angular coordinates, as limiting elements of the discrete
phase space formalism.Comment: Subm. to J. Phys A: Math and Gen. 7 pages, sequel of quant-ph/0108031
(which is to appear on J.Phys A: Math and Gen
Vacuum polarization induced by a uniformly accelerated charge
We consider a point charge fixed in the Rindler coordinates which describe a
uniformly accelerated frame. We determine an integral expression of the induced
charge density due to the vacuum polarization at the first order in the fine
structure constant. In the case where the acceleration is weak, we give
explicitly the induced electrostatic potential.Comment: 13 pages, latex, no figures, to appear in Int. J. Theor. Phys
Exact 1-D Model for Coherent Synchrotron Radiation with Shielding and Bunch Compression
Coherent Synchrotron Radiation has been studied effectively using a
1-dimensional model for the charge distribution in the realm of small angle
approximations and high energies. Here we use Jefimenko's form of Maxwell's
equations, without such approximations, to calculate the exact wake-fields due
to this effect in multiple bends and drifts. It has been shown before that the
influence of a drift can propagate well into a subsequent bend. We show, for
reasonable parameters, that the influence of a previous bend can also propagate
well into a subsequent bend, and that this is especially important at the
beginning of a bend. Shielding by conducting parallel plates is simulated using
the image charge method. We extend the formalism to situations with compressing
and decompressing distributions, and conclude that simpler approximations to
bunch compression usually overestimates the effect. Additionally, an exact
formula for the coherent power radiated by a Gaussian bunch is derived by
considering the coherent synchrotron radiation spectrum, and is used to check
the accuracy of wake-field calculations
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