3,688 research outputs found
Large scale EPR correlations and cosmic gravitational waves
We study how quantum correlations survive at large scales in spite of their
exposition to stochastic backgrounds of gravitational waves. We consider
Einstein-Podolski-Rosen (EPR) correlations built up on the polarizations of
photon pairs and evaluate how they are affected by the cosmic gravitational
wave background (CGWB). We evaluate the quantum decoherence of the EPR
correlations in terms of a reduction of the violation of the Bell inequality as
written by Clauser, Horne, Shimony and Holt (CHSH). We show that this
decoherence remains small and that EPR correlations can in principle survive up
to the largest cosmic scales.Comment: 5 figure
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Defining user perception of distributed multimedia quality
This article presents the results of a study that explored the human side of the multimedia experience. We propose a model that assesses quality variation from three distinct levels: the network, the media and the content levels; and from two views: the technical and the user perspective. By facilitating parameter variation at each of the quality levels and from each of the perspectives, we were able to examine their impact on user quality perception. Results show that a significant reduction in frame rate does not proportionally reduce the user's understanding of the presentation independent of technical parameters, that multimedia content type significantly impacts user information assimilation, user level of enjoyment, and user perception of quality, and that the device display type impacts user information assimilation and user perception of quality. Finally, to ensure the transfer of information, low-level abstraction (network-level) parameters, such as delay and jitter, should be adapted; to maintain the user's level of enjoyment, high-level abstraction quality parameters (content-level), such as the appropriate use of display screens, should be adapted
Transverse-mode coupling in a Kerr medium
We analyze nonlinear transverse mode coupling in a Kerr medium placed in an
optical cavity and its influence on bistability and different kinds of quantum
noise reduction. Even for an input beam that is perfectly matched to a cavity
mode, the nonlinear coupling produces an excess noise in the fluctuations of
the output beam. Intensity squeezing seems to be particularly robust with
respect to mode coupling, while quadrature squeezing is more sensitive.
However, it is possible to find a mode the quadrature squeezing of which is not
affected by the coupling.Comment: 11 pages, 6 figures, LaTe
Generation of three-dimensional prototype models based on cone beam computed tomography
Purpose: The purpose of this study was to generate three-dimensional models based on digital volumetric data that can be used in basic and advanced education. Methods: Four sets of digital volumetric data were established by cone beam computed tomography (CBCT) (Accuitomo, J. Morita, Kyoto, Japan). Datasets were exported as Dicom formats and imported into Mimics and Magic software programs to separate the different tissues such as nerve, tooth and bone. These data were transferred to a Polyjet 3D Printing machine (Eden 330, Object, Israel) to generate the models. Results: Three-dimensional prototype models of certain limited anatomical structures as acquired volumetrically were fabricated. Conclusions: Generating three-dimensional models based on CBCT datasets is possible. Automated routine fabrication of these models, with the given infrastructure, is too time-consuming and therefore too expensiv
Lateral Casimir-Polder force with corrugated surfaces
We derive the lateral Casimir-Polder force on a ground state atom on top of a
corrugated surface, up to first order in the corrugation amplitude. Our
calculation is based on the scattering approach, which takes into account
nonspecular reflections and polarization mixing for electromagnetic quantum
fluctuations impinging on real materials. We compare our first order exact
result with two commonly used approximation methods. We show that the proximity
force approximation (large corrugation wavelengths) overestimates the lateral
force, while the pairwise summation approach underestimates it due to the
non-additivity of dispersion forces. We argue that a frequency shift
measurement for the dipolar lateral oscillations of cold atoms could provide a
striking demonstration of nontrivial geometrical effects on the quantum vacuum.Comment: 12 pages, 6 figures, contribution to QFEXT07 proceeding
Quantum Effects in the Presence of Expanding Semi-Transparent Spherical Mirrors
We study quantum effects in the presence of a spherical semi-transparent
mirror or a system of two concentric mirrors which expand with a constant
acceleration in a flat D-dimensional spacetime. Using the Euclidean approach,
we obtain expressions for fluctuations and the renormalized value of
stress-energy tensor for a scalar non-minimally coupled massless field.
Explicit expressions are obtained for the energy fluxes at the null infinity
generated by such mirrors in the physical spacetime and their properties are
discussed.Comment: 28 pages, Paper is slightly reorganized, additional references are
adde
The Casimir force on a surface with shallow nanoscale corrugations: Geometry and finite conductivity effects
We measure the Casimir force between a gold sphere and a silicon plate with
nanoscale, rectangular corrugations with depth comparable to the separation
between the surfaces. In the proximity force approximation (PFA), both the top
and bottom surfaces of the corrugations contribute to the force, leading to a
distance dependence that is distinct from a flat surface. The measured Casimir
force is found to deviate from the PFA by up to 15%, in good agreement with
calculations based on scattering theory that includes both geometry effects and
the optical properties of the material
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.
Casimir-Polder induced Rabi oscillations
We show that the Casimir-Polder interaction may induce coherent oscillations
between degenerate atomic states. We illustrate this effect by computing the
Casimir-Polder induced Rabi frequency on a Rb atom as it interacts with
a reflecting surface. The atom oscillates between two Zeeman sublevels of its
ground state undergoing a periodic exchange of angular momentum with the vacuum
photons.Comment: minor corrections made to agree with the published versio
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