152 research outputs found
"Supersolid" self-bound Bose condensates via laser-induced interatomic forces
We show that the dipole-dipole interatomic forces induced by a single
off-resonant running laser beam can lead to a self-bound pencil-shaped Bose
condensate, even if the laser beam is a plane-wave. For an appropriate laser
intensity the ground state has a quasi-one dimensional density modulation --- a
Bose "supersolid".Comment: 4 pages, 3 eps figure
I CONSIGLI DI PREFETTURA DELL'ITALIA NAPOLEONICA. ACQUE E STRADE TRA AMMINISTRAZIONE E DISCIPLINAMENTO
An institutional approach on the study of the prefecture councils of the napoleonic Ital
Dipolar Relaxation in an ultra-cold Gas of magnetically trapped chromium atoms
We have investigated both theoretically and experimentally dipolar relaxation
in a gas of magnetically trapped chromium atoms. We have found that the large
magnetic moment of 6 results in an event rate coefficient for dipolar
relaxation processes of up to cms at a magnetic
field of 44 G. We present a theoretical model based on pure dipolar coupling,
which predicts dipolar relaxation rates in agreement with our experimental
observations. This very general approach can be applied to a large variety of
dipolar gases.Comment: 9 pages, 9 figure
Expansion dynamics of a dipolar Bose-Einstein condensate
Our recent measurements on the expansion of a chromium dipolar condensate
after release from an optical trapping potential are in good agreement with an
exact solution of the hydrodynamic equations for dipolar Bose gases. We report
here the theoretical method used to interpret the measurement data as well as
more details of the experiment and its analysis. The theory reported here is a
tool for the investigation of different dynamical situations in time-dependent
harmonic traps.Comment: 12 pages. Submitted to PR
Strong dipolar effects in a quantum ferrofluid
We report on the realization of a Chromium Bose-Einstein condensate (BEC)
with strong dipolar interaction. By using a Feshbach resonance, we reduce the
usual isotropic contact interaction, such that the anisotropic magnetic
dipole-dipole interaction between 52Cr atoms becomes comparable in strength.
This induces a change of the aspect ratio of the cloud, and, for strong dipolar
interaction, the inversion of ellipticity during expansion - the usual "smoking
gun" evidence for BEC - can even be suppressed. These effects are accounted for
by taking into account the dipolar interaction in the superfluid hydrodynamic
equations governing the dynamics of the gas, in the same way as classical
ferrofluids can be described by including dipolar terms in the classical
hydrodynamic equations. Our results are a first step in the exploration of the
unique properties of quantum ferrofluids.Comment: Final, published versio
Depolarisation cooling of an atomic cloud
We propose a cooling scheme based on depolarisation of a polarised cloud of
trapped atoms. Similar to adiabatic demagnetisation, we suggest to use the
coupling between the internal spin reservoir of the cloud and the external
kinetic reservoir via dipolar relaxation to reduce the temperature of the
cloud. By optical pumping one can cool the spin reservoir and force the cooling
process. In case of a trapped gas of dipolar chromium atoms, we show that this
cooling technique can be performed continuously and used to approach the
critical phase space density for BECComment: 8 pages, 5 figure
Observation of dipole-dipole interaction in a degenerate quantum gas
We have investigated the expansion of a Bose-Einstein condensate (BEC) of
strongly magnetic chromium atoms. The long-range and anisotropic magnetic
dipole-dipole interaction leads to an anisotropic deformation of the expanding
Cr-BEC which depends on the orientation of the atomic dipole moments. Our
measurements are consistent with the theory of dipolar quantum gases and show
that a Cr-BEC is an excellent model system to study dipolar interactions in
such gases.Comment: 4 pages, 2 figure
On an exact solution of the Thomas-Fermi equation for a trapped Bose-Einstein condensate with dipole-dipole interactions
We derive an exact solution to the Thomas-Fermi equation for a Bose-Einstein
condensate which has dipole-dipole interactions as well as the usual s-wave
contact interaction, in a harmonic trap. Remarkably, despite the non-local
anisotropic nature of the dipolar interaction the solution is an inverted
parabola, as in the pure s-wave case, but with a different aspect ratio.
Various properties such as electrostriction and stability are discussed.Comment: 11 pages, 5 figure
Production of a chromium Bose-Einstein condensate
The recent achievement of Bose-Einstein condensation of chromium atoms [1]
has opened longed-for experimental access to a degenerate quantum gas with
long-range and anisotropic interaction. Due to the large magnetic moment of
chromium atoms of 6 {}B, in contrast to other Bose- Einstein condensates
(BECs), magnetic dipole-dipole interaction plays an important role in a
chromium BEC. Many new physical properties of degenerate gases arising from
these magnetic forces have been predicted in the past and can now be studied
experimentally. Besides these phenomena, the large dipole moment leads to a
breakdown of standard methods for the creation of a chromium BEC. Cooling and
trapping methods had to be adapted to the special electronic structure of
chromium to reach the regime of quantum degeneracy. Some of them apply
generally to gases with large dipolar forces. We present here a detailed
discussion of the experimental techniques which are used to create a chromium
BEC and alow us to produce pure condensates with up to {} atoms in an
optical dipole trap. We also describe the methods used to determine the
trapping parameters.Comment: 17 pages, 9 figure
Structure and far-infrared edge modes of quantum antidots at zero magnetic field
We have investigated edge modes of different multipolarity sustained by
quantum antidots at zero magnetic field. The ground state of the antidot is
described within a local density functional formalism. Two sum rules, which are
exact within this formalism, have been derived and used to evaluate the energy
of edge collective modes as a function of the surface density and the size of
the antidot.Comment: Typeset using Revtex, 8 pages and 6 Postscript figure
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