4,116 research outputs found
Rayleigh scattering and atomic dynamics in dissipative optical lattices
We investigate Rayleigh scattering in dissipative optical lattices. In particular, following recent proposals [S. Guibal et al., Phys. Rev. Lett. 78, 4709 (1997); C. Jurczak et al., Phys. Rev. Lett. 77, 1727 (1996)], we study whether the Rayleigh resonance originates from the diffraction on a density grating and is therefore a probe of transport of atoms in optical lattices. It turns out that this is not the case: the Rayleigh line is instead a measure of the cooling rate, while spatial diffusion contributes to the scattering spectrum with a much broader resonance
The ALICE Off-Line Strategy: A Successful Migration to OO
The ALICE Experiment has chosen to start developing its software directly in OO, using the services of the ROOT system, which is ALICE's official candidate for the common LHC framework. This had lead to the definition of a complete environment (AliRoot) where the software developed by the different experimental groups is being integrated. Different test-benches for I/O and Simulation have been set up based on real production code. This allows early assessment of technology, both software and hardware in a realistic production environment. Different codes, such as GEANT3, GEANT4 and FLUKA, or the reconstruction algorithms by the physicists developing the detectors, have been easily integrated in the framework, that has shown to be both evolutive and modular.The ALICE Collaboration has adopted this setup and we are now successfully migrating the users into it. This talk describes the AliRoot environment and its future evolution
Cold atom realizations of Brownian motors
Brownian motors are devices which "rectify" Brownian motion, i.e. they can
generate a current of particles out of unbiased fluctuations. Brownian motors
are important for the understanding of molecular motors, and are also promising
for the realization of new nanolelectronic devices. Among the different systems
that can be used to study Brownian motors, cold atoms in optical lattices are
quite an unusual one: there is no thermal bath and both the potential and the
fluctuations are determined by laser fields. In this article recent
experimental implementations of Brownian motors using cold atoms in optical
lattices are reviewed
Stochastic resonance in periodic potentials: realization in a dissipative optical lattice
We have observed the phenomenon of stochastic resonance on the Brillouin
propagation modes of a dissipative optical lattice. Such a mode has been
excited by applying a moving potential modulation with phase velocity equal to
the velocity of the mode. Its amplitude has been characterized by the
center-of-mass (CM) velocity of the atomic cloud. At Brillouin resonance, we
studied the CM-velocity as a function of the optical pumping rate at a given
depth of the potential wells. We have observed a resonant dependence of the CM
velocity on the optical pumping rate, corresponding to the noise strength. This
corresponds to the experimental observation of stochastic resonance in a
periodic potential in the low-damping regime
Shear-free perfect fluids with a solenoidal electric curvature
We prove that the vorticity or the expansion vanishes for any shear-free
perfect fluid solution of the Einstein field equations where the pressure
satisfies a barotropic equation of state and the spatial divergence of the
electric part of the Weyl tensor is zero.Comment: 9 page
Shearfree perfect fluids with solenoidal magnetic curvature and a gamma-law equation of state
We show that shearfree perfect fluids obeying an equation of state p=(gamma
-1) mu are non-rotating or non-expanding under the assumption that the spatial
divergence of the magnetic part of the Weyl tensor is zero.Comment: 11 page
Relationships between various characterisations of wave tails
One can define several properties of wave equations that correspond to the
absence of tails in their solutions, the most common one by far being Huygens'
principle. Not all of these definitions are equivalent, although they are
sometimes assumed to be. We analyse this issue in detail for linear scalar
waves, establishing some relationships between the various properties. Huygens'
principle is almost always equivalent to the characteristic propagation
property, and in two spacetime dimensions the latter is equivalent to the
zeroth order progressing wave propagation property. Higher order progressing
waves in general do have tails, and do not seem to admit a simple physical
characterisation, but they are nevertheless useful because of their close
association with exactly solvable two-dimensional equations.Comment: Plain TeX, 26 page
On the density of states and extinction mean free path of waves in random media: Dispersion relations and sum rules
We establish a fundamental relationship between the averaged density of
states and the extinction mean free path of wave propagating in random media.
From the principle of causality and the Kramers-Kronig relations, we show
that both quantities are connected by dispersion relations and are constrained
by a frequency sum rule. The results are valid under very general conditions
and should be helpful in the analysis of measurements of wave transport through
complex systems and in the design of randomly or periodically structured
materials with specific transport properties.Comment: 2 (double) figures, 8 page
Temperature and spatial diffusion of atoms cooled in a 3D linlin bright optical lattice
We present a detailed experimental study of a three-dimensional linlin
bright optical lattice. Measurements of the atomic temperature and spatial
diffusion coefficients are reported for different angles between the lattice
beams, i.e. for different lattice constants. The experimental findings are
interpretated with the help of numerical simulations. In particular we show,
both experimentally and theoretically, that the temperature is independent of
the lattice constant.Comment: accepted for publication in Eur. Phys. J.
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