89,955 research outputs found
Gravitational Lensing Statistics as a Probe of Dark Energy
By using the comoving distance, we derive an analytic expression for the
optical depth of gravitational lensing, which depends on the redshift to the
source and the cosmological model characterized by the cosmic mass density
parameter , the dark energy density parameter and its
equation of state . It is shown that, the larger the
dark energy density is and the more negative its pressure is, the higher the
gravitational lensing probability is. This fact can provide an independent
constraint for dark energy.Comment: 9 pages, 2 figure
Time-dependent Fr\"ohlich transformation approach for two-atom entanglement generated by successive passage through a cavity
Time-dependent Fr\"ohlich transformations can be used to derive an effective
Hamiltonian for a class of quantum systems with time-dependent perturbations.
We use such a transformation for a system with time-dependent atom-photon
coupling induced by the classical motion of two atoms in an inhomogeneous
electromagnetic field. We calculate the entanglement between the two atoms
resulting from their motion through a cavity as a function of their initial
position difference and velocity.Comment: 7 pages, 3 figure
Gravitational lensing statistical properties in general FRW cosmologies with dark energy component(s): analytic results
Various astronomical observations have been consistently making a strong case
for the existence of a component of dark energy with negative pressure in the
universe. It is now necessary to take the dark energy component(s) into account
in gravitational lensing statistics and other cosmological tests. By using the
comoving distance we derive analytic but simple expressions for the optical
depth of multiple image, the expected value of image separation and the
probability distribution of image separation caused by an assemble of singular
isothermal spheres in general FRW cosmological models with dark energy
component(s). We also present the kinematical and dynamical properties of these
kinds of cosmological models and calculate the age of the universe and the
distance measures, which are often used in classical cosmological tests. In
some cases we are able to give formulae that are simpler than those found
elsewhere in the literature, which could make the cosmological tests for dark
energy component(s) more convenient.Comment: 14 pages, no figure, Latex fil
Entanglement in a two-identical-particle system
The definition of entanglement in identical-particle system is introduced.
The separability criterion in two-identical particle system is given. The
physical meaning of the definition is analysed. Applications to two-boson and
two-fermion systems are made. It is found new entanglement and correlation
phenomena in identical-boson systems exist, and they may have applications in
the field of quantum information.Comment: 4 page
Quantum anti-Zeno effect without rotating wave approximation
In this paper, we systematically study the spontaneous decay phenomenon of a
two-level system under the influences of both its environment and continuous
measurements. In order to clarify some well-established conclusions about the
quantum Zeno effect (QZE) and the quantum anti-Zeno effect (QAZE), we do not
use the rotating wave approximation (RWA) in obtaining an effective
Hamiltonian. We examine various spectral distributions by making use of our
present approach in comparison with other approaches. It is found that with
respect to a bare excited state even without the RWA, the QAZE can still happen
for some cases, e.g., the interacting spectra of hydrogen. But for a physical
excited state, which is a renormalized dressed state of the atomic state, the
QAZE disappears and only the QZE remains. These discoveries inevitably show a
transition from the QZE to the QAZE as the measurement interval changes.Comment: 14 pages, 8 figure
Modeling of the evolution of dielectric loss with processing temperature in ferroelectric and dielectric thin oxide films
It was experimentally found that the evolution of dielectric loss with
processing temperature displays a common trend in ferroelectric and dielectric
thin oxide films: firstly an increase and then a decrease in dielectric loss
when the processing temperature is gradually raised. Such a dielectric response
of ferroelectric/dielectric thin films has been theoretically addressed in this
work. We propose that at the initial stage of the crystallization process in
thin films, the transformation from amorphous to crystalline phase should
increase substantially the dielectric loss; then, with further increase in the
processing temperature, the coalescent growth of small crystalline grains into
big ones could be helpful in reducing the dielectric loss by lowering grain
boundary densities. The obtained experimental data for (Ba,Sr)TiO3 thin films
with 500 nm in thickness were analyzed in terms of the model developed and
shown to be in a reasonable agreement with the theoretical results.Comment: The experimentally observed dielectric loss responses in
ferroelectric and dielectric thin oxide films have been theoretically
addressed in this work, which paves the way for seeking methods in order to
tailor the dielectric loss effectively for practical applications. Accepted
for publication in Journal of Applied Physic
Evidence for spin-flip scattering and local moments in dilute fluorinated graphene
The issue of whether local magnetic moments can be formed by introducing
adatoms into graphene is of intense research interest because it opens the
window to fundamental studies of magnetism in graphene, as well as of its
potential spintronics applications. To investigate this question we measure, by
exploiting the well-established weak localization physics, the phase coherence
length L_phi in dilute fluorinated graphene. L_phi reveals an unusual
saturation below ~ 10 K, which cannot be explained by non-magnetic origins. The
corresponding phase breaking rate increases with decreasing carrier density and
increases with increasing fluorine density. These results provide strong
evidence for spin-flip scattering and points to the existence of adatom-induced
local magnetic moment in fluorinated graphene. Our results will stimulate
further investigations of magnetism and spintronics applications in
adatom-engineered graphene.Comment: 9 pages, 4 figures, and supplementary materials; Phys. Rev. Lett. in
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