468 research outputs found
Damping and frequency shift in the oscillations of two colliding Bose-Einstein condensates
We have investigated the center-of-mass oscillations of a Rb87 Bose-Einstein
condensate in an elongated magneto-static trap. We start from a trapped
condensate and we transfer part of the atoms to another trapped level, by
applying a radio-frequency pulse. The new condensate is produced far from its
equilibrium position in the magnetic potential, and periodically collides with
the parent condensate. We discuss how both the damping and the frequency shift
of the oscillations are affected by the mutual interaction between the two
condensates, in a wide range of trapping frequencies. The experimental data are
compared with the prediction of a mean-field model.Comment: 5 RevTex pages, 7 eps figure
Counterflow of spontaneous mass currents in trapped spin-orbit coupled Fermi gases
We use the Bogoliubov-de Gennes formalism and study the ground-state phases
of trapped spin-orbit coupled Fermi gases in two dimensions. Our main finding
is that the presence of a symmetric (Rashba type) spin-orbit coupling
spontaneously induces counterflowing mass currents in the vicinity of the trap
edge, i.e. and particles circulate in opposite
directions with equal speed. These currents flow even in noninteracting
systems, but their strength decreases toward the molecular BEC limit, which can
be achieved either by increasing the spin-orbit coupling or the interaction
strength. These currents are also quite robust against the effects of
asymmetric spin-orbit couplings in and directions, gradually reducing
to zero as the spin-orbit coupling becomes one dimensional. We compare our
results with those of chiral p-wave superfluids/superconductors.Comment: 6 pages with 4 figures; to appear in PR
Multi-band spectroscopy of inhomogeneous Mott-insulator states of ultracold bosons
In this work, we use inelastic scattering of light to study the response of
inhomogeneous Mott-insulator gases to external excitations. The experimental
setup and procedure to probe the atomic Mott states are presented in detail. We
discuss the link between the energy absorbed by the gases and accessible
experimental parameters as well as the linearity of the response to the
scattering of light. We investigate the excitations of the system in multiple
energy bands and a band-mapping technique allows us to identify band and
momentum of the excited atoms. In addition the momentum distribution in the
Mott states which is spread over the entire first Brillouin zone enables us to
reconstruct the dispersion relation in the high energy bands using a single
Bragg excitation with a fixed momentum transfer.Comment: 19 pages, 7 figure
Boltzmann equation simulation for a trapped Fermi gas of atoms
The dynamics of an interacting Fermi gas of atoms at sufficiently high
temperatures can be efficiently studied via a numerical simulation of the
Boltzmann equation. In this work we describe in detail the setup we used
recently to study the oscillations of two spin-polarised fermionic clouds in a
trap. We focus here on the evaluation of interparticle interactions. We compare
different ways of choosing the phase space coordinates of a pair of atoms after
a successful collision and demonstrate that the exact microscopic setup has no
influence on the macroscopic outcome
Association of ultracold double-species bosonic molecules
We report on the creation of heterospecies bosonic molecules, associated from
an ultracold Bose-Bose mixture of 41K and 87Rb, by using a resonantly modulated
magnetic field close to two Feshbach resonances. We measure the binding energy
of the weakly bound molecular states versus the Feshbach field and compare our
results to theoretical predictions. We observe the broadening and asymmetry of
the association spectrum due to thermal distribution of the atoms, and a
frequency shift occurring when the binding energy depends nonlinearly on the
Feshbach field. A simple model is developed to quantitatively describe the
association process. Our work marks an important step forward in the
experimental route towards Bose-Einstein condensates of dipolar molecules.Comment: 5 pages, 4 figure
Double species condensate with tunable interspecies interactions
We produce Bose-Einstein condensates of two different species, Rb and
K, in an optical dipole trap in proximity of interspecies Feshbach
resonances. We discover and characterize two Feshbach resonances, located
around 35 and 79 G, by observing the three-body losses and the elastic
cross-section. The narrower resonance is exploited to create a double species
condensate with tunable interactions. Our system opens the way to the
exploration of double species Mott insulators and, more in general, of the
quantum phase diagram of the two species Bose-Hubbard model.Comment: 4 pages, 4 figure
Superradiant light scattering from a moving Bose-Einstein condensate
We investigate the interaction of a moving BEC with a far detuned laser beam.
Superradiant Rayleigh scattering arises from the spontaneous formation of a
matter-wave grating due to the interference of two wavepackets with different
momenta. The system is described by the CARL-BEC model which is a
generalization of the Gross-Pitaevskii model to include the self-consistent
evolution of the scattered field. The experiment gives evidence of a damping of
the matter-wave grating which depends on the initial velocity of the
condensate. We describe this damping in terms of a phase-diffusion decoherence
process, in good agreement with the experimental results
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