1,471 research outputs found
Casimir-Polder interaction between an atom and a small magnetodielectric sphere
On the basis of macroscopic quantum electrodynamics and point-scattering
techniques, we derive a closed expression for the Casimir-Polder force between
a ground-state atom and a small magnetodielectric sphere in an arbitrary
environment. In order to allow for the presence of both bodies and media,
local-field corrections are taken into account. Our results are compared with
the known van der Waals force between two ground-state atoms. To continuously
interpolate between the two extreme cases of a single atom and a macroscopic
sphere, we also derive the force between an atom and a sphere of variable
radius that is embedded in an Onsager local-field cavity. Numerical examples
illustrate the theory.Comment: 9 pages, 4 figures, minor addition
Spontaneous decay of an excited atom in an absorbing dielectric
Starting from the quantized version of Maxwell's equations for the
electromagnetic field in an arbitrary linear Kramers-Kronig dielectric,
spontaneous decay of the excited state of a two-level atom embedded in a
dispersive and absorbing medium is studied and the decay rate is calculated.
The calculations are performed for both the (Clausius-Mosotti) virtual cavity
model and the (Glauber-Lewenstein) real cavity model. It is shown that owing to
nonradiative decay associated with absorption the rate of spontaneous decay
sensitively depends on the cavity radius when the atomic transition frequency
approaches an absorption band of the medium. Only when the effect of absorption
is fully disregarded, then the familiar local-field correction factors are
recovered.Comment: 28 pages, 6 figures, typeset using RevTe
Atomic decay near a quantized medium of absorbing scatterers
The decay of an excited atom in the presence of a medium that both scatters
and absorbs radiation is studied with the help of a quantum-electrodynamical
model. The medium is represented by a half space filled with a randomly
distributed set of non-overlapping spheres, which consist of a linear
absorptive dielectric material. The absorption effects are described by means
of a quantized damped-polariton theory. It is found that the effective
susceptibility of the bulk does not fully account for the medium-induced change
in the atomic decay rate. In fact, surface effects contribute to the
modification of the decay properties as well. The interplay of scattering and
absorption in the total decay rate is discussed.Comment: 20 pages, 1 figur
Black Hole Area in Brans-Dicke Theory
We have shown that the dynamics of the scalar field
in Brans-Dicke theories of gravity makes the surface area of the black hole
horizon {\it oscillatory} during its dynamical evolution. It explicitly
explains why the area theorem does not hold in Brans-Dicke theory. However, we
show that there exists a certain non-decreasing quantity defined on the event
horizon which is proportional to the black hole entropy for the case of
stationary solutions in Brans-Dicke theory. Some numerical simulations have
been demonstrated for Oppenheimer-Snyder collapse in Brans-Dicke theory.Comment: 12 pages, latex, 5 figures, epsfig.sty, some statements clarified and
two references added, to appear in Phys. Rev.
Waveform propagation in black hole spacetimes: evaluating the quality of numerical solutions
We compute the propagation and scattering of linear gravitational waves off a
Schwarzschild black hole using a numerical code which solves a generalization
of the Zerilli equation to a three dimensional cartesian coordinate system.
Since the solution to this problem is well understood it represents a very good
testbed for evaluating our ability to perform three dimensional computations of
gravitational waves in spacetimes in which a black hole event horizon is
present.Comment: 13 pages, RevTeX, to appear in Phys. Rev.
Bose-Einstein Condensation on a Permanent-Magnet Atom Chip
We have produced a Bose-Einstein condensate on a permanent-magnet atom chip
based on periodically magnetized videotape. We observe the expansion and
dynamics of the condensate in one of the microscopic waveguides close to the
surface. The lifetime for atoms to remain trapped near this dielectric material
is significantly longer than above a metal surface of the same thickness. These
results illustrate the suitability of microscopic permanent-magnet structures
for quantum-coherent preparation and manipulation of cold atoms.Comment: 4 pages, 6 figures, Published in Phys. Rev. A, Rapid Com
Targeted large mass ratio numerical relativity surrogate waveform model for GW190814
Gravitational wave observations of large mass ratio compact binary mergers like GW190814 highlight the need for reliable, high-accuracy waveform templates for such systems. We present NRHybSur2dq15, a new surrogate model trained on hybridized numerical relativity (NR) waveforms with mass ratios , and aligned spins and . We target the parameter space of GW190814-like events as large mass ratio NR simulations are very expensive. The model includes the (2,2), (2,1), (3,3), (4,4), and (5,5) spin-weighted spherical harmonic modes, and spans the entire LIGO bandwidth (with Hz) for total masses . NRHybSur2dq15 accurately reproduces the hybrid waveforms, with mismatches below for total masses . This is at least an order of magnitude improvement over existing semi-analytical models for GW190814-like systems. Finally, we reanalyze GW190814 with the new model and obtain source parameter constraints consistent with previous work
Dynamical evolution of boson stars in Brans-Dicke theory
We study the dynamics of a self-gravitating scalar field solitonic object
(boson star) in the Jordan-Brans-Dicke (BD) theory of gravity. We show
dynamical processes of this system such as (i) black hole formation of
perturbed equilibrium configuration on an unstable branch; (ii) migration of
perturbed equilibrium configuration from the unstable branch to stable branch;
(iii) transition from excited state to a ground state. We find that the
dynamical behavior of boson stars in BD theory is quite similar to that in
general relativity (GR), with comparable scalar wave emission. We also
demonstrate the formation of a stable boson star from a Gaussian scalar field
packet with flat gravitational scalar field initial data. This suggests that
boson stars can be formed in the BD theory in much the same way as in GR.Comment: 13 pages by RevTeX, epsf.sty, 16 figures, comments added, refs
updated, to appear in Phys. Rev.
Bose-Einstein Condensation on a Permanent-Magnet Atom Chip
We have produced a Bose-Einstein condensate on a permanent-magnet atom chip
based on periodically magnetized videotape. We observe the expansion and
dynamics of the condensate in one of the microscopic waveguides close to the
surface. The lifetime for atoms to remain trapped near this dielectric material
is significantly longer than above a metal surface of the same thickness. These
results illustrate the suitability of microscopic permanent-magnet structures
for quantum-coherent preparation and manipulation of cold atoms.Comment: 4 pages, 6 figures, Published in Phys. Rev. A, Rapid Com
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