1,520 research outputs found
Quantum Limits in Space-Time Measurements
Quantum fluctuations impose fundamental limits on measurement and space-time
probing. Although using optimised probe fields can allow to push sensitivity in
a position measurement beyond the "standard quantum limit", quantum
fluctuations of the probe field still result in limitations which are
determined by irreducible dissipation mechanisms. Fluctuation-dissipation
relations in vacuum characterise the mechanical effects of radiation pressure
vacuum fluctuations, which lead to an ultimate quantum noise for positions. For
macroscopic reflectors, the quantum noise on positions is dominated by
gravitational vacuum fluctuations, and takes a universal form deduced from
quantum fluctuations of space-time curvatures in vacuum. These can be
considered as ultimate space-time fluctuations, fixing ultimate quantum limits
in space-time measurements.Comment: 11 pages, to appear in Quantum and Semiclassical Optic
Test of Guttmann and Enting's conjecture in the eight-vertex model
We investigate the analyticity property of the partially resummed series
expansion(PRSE) of the partition function for the eight-vertex model.
Developing a graphical technique, we have obtained a first few terms of the
PRSE and found that these terms have a pole only at one point in the complex
plane of the coupling constant. This result supports the conjecture proposed by
Guttmann and Enting concerning the ``solvability'' in statistical mechanical
lattice models.Comment: 15 pages, 3 figures, RevTe
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
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
Radiation Pressure as a Source of Decoherence
We consider the interaction of an harmonic oscillator with the quantum field
via radiation pressure. We show that a `Schrodinger cat' state decoheres in a
time scale that depends on the degree of `classicality' of the state
components, and which may be much shorter than the relaxation time scale
associated to the dynamical Casimir effect. We also show that decoherence is a
consequence of the entanglement between the quantum states of the oscillator
and field two-photon states. With the help of the fluctuation-dissipation
theorem, we derive a relation between decoherence and damping rates valid for
arbitrary values of the temperature of the field. Coherent states are selected
by the interaction as pointer states.Comment: 14 pages, 3 figures, RevTex fil
Vacuum fluctuations, accelerated motion and conformal frames
Radiation from a mirror moving in vacuum electromagnetic fields is shown to
vanish in the case of a uniformly accelerated motion. Such motions are related
to conformal coordinate transformations, which preserve correlation functions
characteristic of vacuum fluctuations. As a result, vacuum fluctuations remain
invariant under reflection upon a uniformly accelerated mirror, which therefore
does not radiate and experiences no radiation reaction force. Mechanical
effects of vacuum fluctuations thus exhibit an invariance with respect to
uniformly accelerated motions.Comment: 7 page
Gravitational decoherence of planetary motions
We study the effect of the scattering of gravitational waves on planetary
motions, say the motion of the Moon around the Earth. Though this effect has a
negligible influence on dissipation, it dominates fluctuations and the
associated decoherence mechanism, due to the very high effective temperature of
the background of gravitational waves in our galactic environment.Comment: 6 pages, no figure, to appear in EuroPhysics Letters; needs `epl.cls
Inertial forces in the Casimir effect with two moving plates
We combine linear response theory and dimensional regularization in order to
derive the dynamical Casimir force in the low frequency regime. We consider two
parallel plates moving along the normal direction in dimensional space. We
assume the free-space values for the mass of each plate to be known, and obtain
finite, separation-dependent mass corrections resulting from the combined
effect of the two plates. The global mass correction is proportional to the
static Casimir energy, in agreement with Einstein's law of equivalence between
mass and energy for stressed rigid bodies.Comment: 9 pages, 1 figure; title and abstract changed; to appear in Physical
Review
Stochastic Spacetime and Brownian Motion of Test Particles
The operational meaning of spacetime fluctuations is discussed. Classical
spacetime geometry can be viewed as encoding the relations between the motions
of test particles in the geometry. By analogy, quantum fluctuations of
spacetime geometry can be interpreted in terms of the fluctuations of these
motions. Thus one can give meaning to spacetime fluctuations in terms of
observables which describe the Brownian motion of test particles. We will first
discuss some electromagnetic analogies, where quantum fluctuations of the
electromagnetic field induce Brownian motion of test particles. We next discuss
several explicit examples of Brownian motion caused by a fluctuating
gravitational field. These examples include lightcone fluctuations, variations
in the flight times of photons through the fluctuating geometry, and
fluctuations in the expansion parameter given by a Langevin version of the
Raychaudhuri equation. The fluctuations in this parameter lead to variations in
the luminosity of sources. Other phenomena which can be linked to spacetime
fluctuations are spectral line broadening and angular blurring of distant
sources.Comment: 15 pages, 3 figures. Talk given at the 9th Peyresq workshop, June
200
Post-Einsteinian tests of linearized gravitation
The general relativistic treatment of gravitation can be extended by
preserving the geometrical nature of the theory but modifying the form of the
coupling between curvature and stress tensors. The gravitation constant is thus
replaced by two running coupling constants which depend on scale and differ in
the sectors of traceless and traced tensors. When calculated in the solar
system in a linearized approximation, the metric is described by two
gravitation potentials. This extends the parametrized post-Newtonian (PPN)
phenomenological framework while allowing one to preserve compatibility with
gravity tests performed in the solar system. Consequences of this extension are
drawn here for phenomena correctly treated in the linear approximation. We
obtain a Pioneer-like anomaly for probes with an eccentric motion as well as a
range dependence of Eddington parameter to be seen in light deflection
experiments.Comment: 15 pages. Accepted version, to appear in Classical and Quantum
Gravit
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