5,193 research outputs found
Measurement of atomic diffraction phases induced by material gratings
Atom-surface interactions can significantly modify the intensity and phase of
atom de Broglie waves diffracted by a silicon nitride grating. This affects the
operation of a material grating as a coherent beam splitter. The phase shift
induced by diffraction is measured by comparing the relative phases of serveral
interfering paths in a Mach-Zehnder Na atom interferometer formed by three
material gratings. The values of the diffraction phases are consistent with a
simple model which includes a van der Waals atom-surface interaction between
the Na atoms and the silicon nitride grating bars.Comment: 4 pages, 5 figures, submitted to PR
Si3N4 emissivity and the unidentified infrared bands
Infrared spectroscopy of warm (about 150 to 750 K), dusty astronomical sources has revealed a structured emission spectrum which can be diagnostic of the composition, temperature, and in some cases, even size and shape of the grains giving rise to the observed emission. The identifications of silicate emission in oxygen rich objects and SiC in carbon rich object are two examples of this type of analysis. Cometary spectra at moderate resolution have similarly revealed silicate emission, tying together interstellar and interplanetary dust. However, Goebel has pointed out that some astronomical sources appear to contain a different type of dust which results in a qualitatively different spectral shape in the 8 to 13 micron region. The spectra shown make it appear unlikely that silicon nitride can be identified as the source of the 8 to 13 micron emission in either NGC 6572 or Nova Aql 1982. The similarity between the general wavelength and shape of the 10 micron emission from some silicates and that from the two forms of silicon nitride reported could allow a mix of cosmic grains which include some silicon nitride if only the 8 to 13 micron data are considered
Observing the Profile of an Atom Laser Beam
We report on an investigation of the beam profile of an atom laser extracted
from a magnetically trapped Rb Bose-Einstein condensate. The transverse
momentum distribution is magnified by a curved mirror for matter waves and a
momentum resolution of 1/60 of a photon recoil is obtained. We find the
transverse momentum distribution to be determined by the mean-field potential
of the residing condensate, which leads to a non-smooth transverse density
distribution. Our experimental data are compared with a full 3D simulation of
the output coupling process and we find good agreement.Comment: 4 pages, 4 figure
Mass and Spin of Poincare Gauge Theory
We discuss two expressions for the conserved quantities (energy momentum and
angular momentum) of the Poincar\'e Gauge Theory. We show, that the variations
of the Hamiltonians, of which the expressions are the respective boundary
terms, are well defined, if we choose an appropriate phase space for asymptotic
flat gravitating systems. Furthermore, we compare the expressions with others,
known from the literature.Comment: 16 pages, plain-tex; to be published in Gen. Rel. Gra
Image Storage in Hot Vapors
We theoretically investigate image propagation and storage in hot atomic
vapor. A system is adopted for imaging and an atomic vapor cell is placed
over the transform plane. The Fraunhofer diffraction pattern of an object in
the object plane can thus be transformed into atomic Raman coherence according
to the idea of ``light storage''. We investigate how the stored diffraction
pattern evolves under diffusion. Our result indicates, under appropriate
conditions, that an image can be reconstructed with high fidelity. The main
reason for this procedure to work is the fact that diffusion of opposite-phase
components of the diffraction pattern interfere destructively.Comment: 11 pages, 3 figure
Weak Value in Wave Function of Detector
A simple formula to read out the weak value from the wave function of the
measuring device after the postselection with the initial Gaussian profile is
proposed. We apply this formula for the weak value to the classical experiment
of the realization of the weak measurement by the optical polarization and
obtain the weak value for any pre- and post-selections. This formula
automatically includes the interference effect which is necessary to yields the
weak value as an outcome of the weak measurement.Comment: 3 pages, no figures, Published in Journal of the Physical Society of
Japa
Diffraction limit of the sub-Planck structures
The orthogonality of cat and displaced cat states, underlying Heisenberg
limited measurement in quantum metrology, is studied in the limit of large
number of states. The asymptotic expression for the corresponding state overlap
function, controlled by the sub-Planck structures arising from phase space
interference, is obtained exactly. The validity of large phase space support,
in which context the asymptotic limit is achieved, is discussed in detail. For
large number of coherent states, uniformly located on a circle, it identically
matches with the diffraction pattern for a circular ring with uniform angular
source strength. This is in accordance with the van Cittert-Zernike theorem,
where the overlap function, similar to the mutual coherence function matches
with a diffraction pattern.Comment: 5 pages, 3 figure
Nucleon mass and pion loops: Renormalization
Using Dyson--Schwinger equations, the nucleon propagator is analyzed
nonperturbatively in a field--theoretical model for the pion--nucleon
interaction. Infinities are circumvented by using pion--nucleon form factors
which define the physical scale. It is shown that the correct, finite,
on--shell nucleon renormalization is important for the value of the mass--shift
and the propagator. For physically acceptable forms of the pion--nucleon form
factor the rainbow approximation together with renormalization is inconsistent.
Going beyond the rainbow approximation, the full pion--nucleon vertex is
modelled by its bare part plus a one--loop correction including an effective
. It is found that a consistent value for the nucleon mass--shift can
be obtained as a consequence of a subtle interplay between wave function and
vertex renormalization. Furthermore, the bare and renormalized pion--nucleon
coupling constant are approximately equal, consistent with results from the
Cloudy Bag Model.Comment: 14 pages, 6 figure
A Stability Diagram for Dense Suspensions of Model Colloidal Al2O3-Particles in Shear Flow
In Al2O3 suspensions, depending on the experimental conditions very different
microstructures can be found, comprising fluid like suspensions, a repulsive
structure, and a clustered microstructure. For technical processing in
ceramics, the knowledge of the microstructure is of importance, since it
essentially determines the stability of a workpiece to be produced. To
enlighten this topic, we investigate these suspensions under shear by means of
simulations. We observe cluster formation on two different length scales: the
distance of nearest neighbors and on the length scale of the system size. We
find that the clustering behavior does not depend on the length scale of
observation. If inter-particle interactions are not attractive the particles
form layers in the shear flow. The results are summarized in a stability
diagram.Comment: 15 pages, 10 figures, revised versio
Rigorous formulation of oblique incidence scattering from dispersive media
We formulate a finite-difference time-domain (FDTD) approach to simulate
electromagnetic wave scattering from scatterers embedded in layered dielectric
or dispersive media. At the heart of our approach is a derivation of an
equivalent one-dimensional wave propagation equation for dispersive media
characterized by a linear sum of Debye-, Drude- and Lorentz-type poles. The
derivation is followed by a detailed discussion of the simulation setup and
numerical issues. The developed methodology is tested by comparison with
analytical reflection and transmission coefficients for scattering from a slab,
illustrating good convergence behavior. The case of scattering from a
sub-wavelength slit in a dispersive thin film is explored to demonstrate the
applicability of our formulation to time- and incident angle-dependent analysis
of surface waves generated by an obliquely incident plane wave.Comment: 35 pages, 8 figures, 4 table
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