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 lin⊥\perplin bright optical lattice

We present a detailed experimental study of a three-dimensional lin$\perp$lin 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.