2,406 research outputs found
Laser scattering by density fluctuations of ultra-cold atoms in a magneto-optical trap
We study the spectrum of density fluctuations in the ultra-cold gas of
neutral atoms, confined in a magneto-optical trap. We determine the
corresponding amplitude and spectra of laser light scattered by this medium. We
derive an expression for the dynamical structure function, by using a test
particle method. We propose to use the collective laser scattering as a
diagnostic method for the microscopic properties of the ultra-cold matter. This
will also allow us to check on the atomic correlations which are mediated by
the collective mean field inside the gas.Comment: J. Phys. B (in press
Classical Rotons in Cold Atomic Traps
We predict the emergence of a roton minimum in the dispersion relation of
elementary excitations in cold atomic gases in the presence of diffusive light.
In large magneto-topical traps, multiple-scattering of light is responsible for
the collective behavior of the system, which is associated to an effective
Coulomb-like interaction between the atoms. In optically thick clouds, the
re-scattered light undergoes diffusive propagation, which is responsible for a
stochastic short-range force acting on the atoms. We show that the dynamical
competition between these two forces results on a new polariton mode, which
exhibits a roton minimum. Making use of Feynman's formula for the static
structure factor, we show that the roton minimum is related to the appearance
of long-range order in the system.Comment: 5 pages, 3 figure
Rossby waves in rapidly rotating Bose-Einstein condensates
We predict and describe a new collective mode in rotating Bose-Einstein
condensates, which is very similar to the Rossby waves in geophysics. In the
regime of fast rotation, the Coriolis force dominates the dynamics and acts as
a restoring force for acoustic-drift waves along the condensate. We derive a
nonlinear equation that includes the effects of both the zero-point pressure
and the anharmonicity of the trap. It is shown that such waves have negative
phase speed, propagating in the opposite sense of the rotation. We discuss
different equilibrium configurations and compare with those resulting from the
Thomas-Fermi approximation.Comment: 4 pages, 2 figures (submitted to PRL
Photon Orbital Angular Momentum and Mass in a Plasma Vortex
We analyse the Anderson-Higgs mechanism of photon mass acquisition in a
plasma and study the contribution to the mass from the orbital angular momentum
acquired by a beam of photons when it crosses a spatially structured charge
distribution. To this end we apply Proca-Maxwell equations in a static plasma
with a particular spatial distribution of free charges, notably a plasma
vortex, that is able to impose orbital angular momentum (OAM) onto light. In
addition to the mass acquisition of the conventional Anderson-Higgs mechanism,
we find that the photon acquires an additional mass from the OAM and that this
mass reduces the Proca photon mass.Comment: Four pages, no figures. Error corrections, improved notation, refined
derivation
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