453 research outputs found
Quantum erasure within the Optical Stern-Gerlach Model
In the optical Stern-Gerlach effect the two branches in which the incoming
atomic packet splits up can display interference pattern outside the cavity
when a field measurement is made which erases the which-way information on the
quantum paths the system can follow. On the contrary, the mere possibility to
acquire this information causes a decoherence effect which cancels out the
interference pattern. A phase space analysis is also carried out to investigate
on the negativity of the Wigner function and on the connection between its
covariance matrix and the distinguishability of the quantum paths.Comment: 7 pages, 3 figure
Non-perturbative results for the spectrum of surface-disordered waveguides
We calculated the spectrum of normal scalar waves in a planar waveguide with
absolutely soft randomly rough boundaries beyond the perturbation theories in
the roughness heights and slopes, basing on the exact boundary scattering
potential. The spectrum is proved to be a nearly real non-analytic function of
the dispersion of the roughness heights (with square-root
singularity) as . The opposite case of large boundary defects is
summarized.Comment: REVTEX 3, OSA style, 9 pages, no figures. Submitted to Optics Letter
Analytical Modeling and Multiphysics Simulation of Acousto-Electromagnetic Interaction
A model for interaction between acoustic and elec- tromagnetic waves based on photoelasticity is presented. A radar equation based on physical, geometric and system parameters is shown, as well as a condition for maximizing interaction (equivalent to the Bragg condition in acousto-optics). The photoelastic model is used to implement a multiphysics simulation of the problem. The Bragg condition is shown to hold for the simulated case. Additionally, simulations are used to show how a contrast in material properties in a small inclusion affects the interaction
Ambiguities in the HBT approach to determine the interaction regions
The necessary and sufficient condition for a quantity to be measurable by the
HBT method is given and discussed.Comment: Report at the conference QCD08, July 2008, LateX 8 pages, no figure
Scattering of Gravitational Waves by the Weak Gravitational Fields of Lens Objects
We consider the scattering of the gravitational waves by the weak
gravitational fields of lens objects. We obtain the scattered gravitational
waveform by treating the gravitational potential of the lens to first order,
i.e. using the Born approximation. We find that the effect of scattering on the
waveform is roughly given by the Schwarzschild radius of the lens divided by
the wavelength of gravitational wave for a compact lens object. If the lenses
are smoothly distributed, the effect of scattering is of the order of the
convergence field along the line of sight to the source. In the short
wavelength limit, the amplitude is magnified by , which is consistent
with the result in weak gravitational lensing.Comment: 4 pages, 2 figures, A&A Letters, in press, minor changes, references
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Effective Dielectric Tensor for Electromagnetic Wave Propagation in Random Media
We derive exact strong-contrast expansions for the effective dielectric
tensor \epeff of electromagnetic waves propagating in a two-phase composite
random medium with isotropic components explicitly in terms of certain
integrals over the -point correlation functions of the medium. Our focus is
the long-wavelength regime, i.e., when the wavelength is much larger than the
scale of inhomogeneities in the medium. Lower-order truncations of these
expansions lead to approximations for the effective dielectric constant that
depend upon whether the medium is below or above the percolation threshold. In
particular, we apply two- and three-point approximations for \epeff to a
variety of different three-dimensional model microstructures, including
dispersions of hard spheres, hard oriented spheroids and fully penetrable
spheres as well as Debye random media, the random checkerboard, and
power-law-correlated materials. We demonstrate the importance of employing
-point correlation functions of order higher than two for high
dielectric-phase-contrast ratio. We show that disorder in the microstructure
results in an imaginary component of the effective dielectric tensor that is
directly related to the {\it coarseness} of the composite, i.e., local
volume-fraction fluctuations for infinitely large windows. The source of this
imaginary component is the attenuation of the coherent homogenized wave due to
scattering. We also remark on whether there is such attenuation in the case of
a two-phase medium with a quasiperiodic structure.Comment: 40 pages, 13 figure
Atmosphere-like turbulence generation with surface-etched phase-screens
We built and characterized an optical system that emulates the optical
characteristics of an 8m-class telescope like the Very Large Telescope. The
system contains rotating glass phase-screens to generate realistic
atmosphere-like optical turbulence, as needed for testing multi-conjugate
adaptive optics systems. In this paper we present an investigation of the
statistical properties of two phase-screens etched on glass-plate surfaces,
obtained from Silios Technologies. Those etched screens are highly transmissive
(above 85%) from 0.45 to 2.5 microns. From direct imaging, their Fried
parameter r0 values (0.43+-0.04 mm and 0.81+-0.03 mm, respectively, at 0.633
microns) agree with the expectation to within 10%. This is also confirmed by a
comparison of measured and expected Zernike coefficient variances. Overall, we
find that those screens are quite reproducible, allowing sub-millimetre r0
values, which were difficult to achieve in the past. We conclude that the
telescope emulator and phase-screens form a powerful atmospheric turbulence
generator allowing systematic testing of different kinds of AO instrumentation.Comment: 10 pages, 8 figures, 3 mpeg movies. Submitted to Optics Expres
Exact positivity of the Wigner and P-functions of a Markovian open system
We discuss the case of a Markovian master equation for an open system, as it
is frequently found from environmental decoherence. We prove two theorems for
the evolution of the quantum state. The first one states that for a generic
initial state the corresponding Wigner function becomes strictly positive after
a finite time has elapsed. The second one states that also the P-function
becomes exactly positive after a decoherence time of the same order. Therefore
the density matrix becomes exactly decomposable into a mixture of Gaussian
pointer states.Comment: 11 pages, references added, typo corrected, to appear in J. Phys.
Statistics of dressed modes in a thermal state
By a Wigner-function calculation, we evaluate the trace of a certain Gaussian
operator arising in the theory of a boson system subject to both finite
temperature and (weak) interaction. Thereby we rederive (and generalize) a
recent result by Kocharovsky, Kocharovsky, and Scully [Phys. Rev. A, vol. 61,
art. 053606 (2000)] in a way that is technically much simpler. One step uses a
special case of the response of Wigner functions to linear transformations, and
we demonstrate the general case by simple means. As an application we extract
the counting statistics for each mode of the Bose gas.Comment: to appear in Optics Communications, 10 page
Accurate seeing measurements with MASS and DIMM
Astronomical seeing is quantified by a single parameter, turbulence integral,
in the framework of the Kolmogorov turbulence model. This parameter can be
routinely measured by a Differential Image Motion Monitor, DIMM. A new
instrument, Multi-Aperture Scintillation Sensor (MASS), permits to measure the
seeing in the free atmosphere above ~0.5km and, together with a DIMM, to
estimate the ground-layer seeing. The absolute accuracy of both methods is
studied here using analytical theory, numerical simulation, and experiments. A
modification of the MASS data processing to compensate for partially saturated
scintillation is developed. We find that the DIMM can be severely biased by
optical aberrations (e.g. defocus) and propagation. Seeing measurements with
DIMM and MASS can reach absolute accuracy of ~10% when their biases are
carefully controlled. Pushing this limit to 1% appears unrealistic because the
seeing itself is just a model-dependent parameter of a non-stationary random
process.Comment: 13 pages, 14 figures. Accepted for publication in MNRA
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