1,025 research outputs found
Intensity correlations and mesoscopic fluctuations of diffusing photons in cold atoms
We study the angular correlation function of speckle patterns that result
from multiple scattering of photons by cold atomic clouds. We show that this
correlation function becomes larger than the value given by Rayleigh law for
classical scatterers. These large intensity fluctuations constitute a new
mesoscopic interference effect specific to atom-photon interactions, that could
not be observed in other systems such as weakly disordered metals. We provide a
complete description of this behavior and expressions that allow for a
quantitative comparison with experiments.Comment: 4 pages, 2 figure
The Feshbach-Kerman-Koonin multistep direct reaction theory
The multistep direct reaction theory of Feshbach, Kerman and Koonin (1980) is described in detail and compared with other theories. The results of several analyses of experimental cross-sections are described, and the validity and usefulness of the theory assessed
Non-Gaussian fluctuations of mesoscopic persistent currents
The persistent current in an ensemble of normal-metal rings shows Gaussian
distributed sample-to-sample fluctuations with non-Gaussian corrections, which
are precursors of the transition into the Anderson localized regime. We here
report a calculation of the leading non-Gaussian correction to the current
autocorrelation function, which is of third order in the current. Although the
third-order correlation function is small, inversely proportional to the
dimensionless conductance of the ring, the mere fact that it is nonzero is
remarkable, since it is an odd moment of the current distribution.Comment: 4+ pages, 2 figure
Near-field interactions and non-universality in speckle patterns produced by a point source in a disordered medium
A point source in a disordered scattering medium generates a speckle pattern
with non-universal features, giving rise to the so-called C_0 correlation. We
analyze theoretically the relationship between the C_0 correlation and the
statistical fluctuations of the local density of states, based on simple
arguments of energy conservation. This derivation leads to a clear physical
interpretation of the C_0 correlation. Using exact numerical simulations, we
show that C_0 is essentially a correlation resulting from near-field
interactions. These interactions are responsible for the non-universality of
C_0, that confers to this correlation a huge potential for sensing and imaging
at the subwavelength scale in complex media
Three-dimensionality in quasi-two dimensional flows: recirculations and barrel effects
A scenario is put forward for the appearance of three-dimensionality both in
quasi-2D rotating flows and quasi-2D magnetohydrodynamic (MHD) flows. We show
that 3D recirculating flows and currents originate in wall boundary layers and
that, unlike in ordinary hydrodynamic flows, they cannot be ignited by
confinement alone. They also induce a second form of three-dimensionality with
quadratic variations of velocities and current across the channel. This
scenario explains both the common tendency of these flows to two-dimensionality
and the mechanisms of the recirculations through a single formal analogy
covering a wide class of flow including rotating and MHD flows. These
trans-disciplinary effects are thus active in atmospheres, oceans or the
cooling blankets of nuclear fusion reactors.Comment: 6 pages, 1 Figur
Vortex nucleation through edge states in finite Bose-Einstein condensates
We study the vortex nucleation in a finite Bose-Einstein condensate. Using a
set of non-local and chiral boundary conditions to solve the
Schrdinger equation of non-interacting bosons in a rotating trap, we
obtain a quantitative expression for the characteristic angular velocity for
vortex nucleation in a condensate which is found to be 35% of the transverse
harmonic trapping frequency.Comment: 24 pages, 8 figures. Both figures and the text have been revise
An electronic Mach-Zehnder interferometer in the Fractional Quantum Hall effect
We compute the interference pattern of a Mach-Zehnder interferometer
operating in the fractional quantum Hall effect. Our theoretical proposal is
inspired by a remarkable experiment on edge states in the Integer Quantum Hall
effect (IQHE). The Luttinger liquid model is solved via two independent
methods: refermionization at nu=1/2 and the Bethe Ansatz solution available for
Laughlin fractions. The current differs strongly from that of single electrons
in the strong backscattering regime. The Fano factor is periodic in the flux,
and it exhibits a sharp transition from sub-Poissonian (charge e/2) to
Poissonian (charge e) in the neighborhood of destructive interferences
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