161 research outputs found
Strongly inhibited transport of a 1D Bose gas in a lattice
We report the observation of strongly damped dipole oscillations of a quantum
degenerate 1D atomic Bose gas in a combined harmonic and optical lattice
potential. Damping is significant for very shallow axial lattices (0.25 photon
recoil energies), and increases dramatically with increasing lattice depth,
such that the gas becomes nearly immobile for times an order of magnitude
longer than the single-particle tunneling time. Surprisingly, we see no
broadening of the atomic quasimomentum distribution after damped motion. Recent
theoretical work suggests that quantum fluctuations can strongly damp dipole
oscillations of 1D atomic Bose gas, providing a possible explanation for our
observations.Comment: 5 pages, 4 figure
Cooling of a Bose-Einstein Condensate by spin distillation
We propose and experimentally demonstrate a new cooling mechanism leading to
purification of a spinor Bose-Einstein Condensate (BEC). Our scheme starts with
a BEC polarized in the lowest energy spin state. Spin excited states are
thermally populated by lowering the single particle energy gap set by the
magnetic field. Then these spin-excited thermal components are filtered out,
which leads to an increase of the BEC fraction. We experimentally demonstrate
such cooling for a spin 3 52Cr dipolar BEC. Our scheme should be applicable to
Na or Rb, with perspective to reach temperatures below 1 nK.Comment: 4 figure
Three-body recombination in a three-state Fermi gas with widely tunable interactions
We investigate the stability of a three spin state mixture of ultracold
fermionic Li atoms over a range of magnetic fields encompassing three
Feshbach resonances. For most field values, we attribute decay of the atomic
population to three-body processes involving one atom from each spin state and
find that the three-body loss coefficient varies by over four orders of
magnitude. We observe high stability when at least two of the three scattering
lengths are small, rapid loss near the Feshbach resonances, and two unexpected
resonant loss features. At our highest fields, where all pairwise scattering
lengths are approaching , we measure a three-body loss
coefficient and a trend
toward lower decay rates for higher fields indicating that future studies of
color superfluidity and trion formation in a SU(3) symmetric Fermi gas may be
feasible
Dipolar atomic spin ensembles in a double-well potential
We experimentally study the spin dynamics of mesoscopic ensembles of
ultracold magnetic spin-3 atoms located in two separated wells of an optical
dipole trap. We use a radio-frequency sweep to selectively flip the spin of the
atoms in one of the wells, which produces two separated spin domains of
opposite polarization. We observe that these engineered spin domains are
metastable with respect to the long-range magnetic dipolar interactions between
the two ensembles. The absence of inter-cloud dipolar spin-exchange processes
reveals a classical behavior, in contrast to previous results with atoms loaded
in an optical lattice. When we merge the two subsystems, we observe
spin-exchange dynamics due to contact interactions which enable the first
determination of the s-wave scattering length of 52Cr atoms in the S=0
molecular channel a_0=13.5^{+11}_{-10.5}a_B (where a_B is the Bohr radius).Comment: 9 pages, 7 figure
Universality in Three- and Four-Body Bound States of Ultracold Atoms
Under certain circumstances, three or more interacting particles may form
bound states. While the general few-body problem is not analytically solvable,
the so-called Efimov trimers appear for a system of three particles with
resonant two-body interactions. The binding energies of these trimers are
predicted to be universally connected to each other, independent of the
microscopic details of the interaction. By exploiting a Feshbach resonance to
widely tune the interactions between trapped ultracold lithium atoms, we find
evidence for two universally connected Efimov trimers and their associated
four-body bound states. A total of eleven precisely determined three- and
four-body features are found in the inelastic loss spectrum. Their relative
locations on either side of the resonance agree well with universal theory,
while a systematic deviation from universality is found when comparing features
across the resonance.Comment: 16 pages including figures and Supplementary Online Materia
Non-equilibrium quantum magnetism in a dipolar lattice gas
Research on quantum magnetism with ultra-cold gases in optical lattices is
expected to open fascinating perspectives for the understanding of fundamental
problems in condensed-matter physics. Here we report on the first realization
of quantum magnetism using a degenerate dipolar gas in an optical lattice. In
contrast to their non-dipolar counterparts, dipolar lattice gases allow for
inter-site spin-spin interactions without relying on super-exchange energies,
which constitutes a great advantage for the study of spin lattice models. In
this paper we show that a chromium gas in a 3D lattice realizes a lattice model
resembling the celebrated t-J model, which is characterized by a
non-equilibrium spinor dynamics resulting from inter-site Heisenberg-like
spin-spin interactions provided by non-local dipole-dipole interactions.
Moreover, due to its large spin, chromium lattice gases constitute an excellent
environment for the study of quantum magnetism of high-spin systems, as
illustrated by the complex spin dynamics observed for doubly-occupied sites.Comment: 10 pages, 5+5 figure
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