151 research outputs found
Production of Long-Lived Ultracold Li2 Molecules from a Fermi gas
We create weakly-bound Li2 molecules from a degenerate two component Fermi
gas by sweeping a magnetic field across a Feshbach resonance. The atom-molecule
transfer efficiency can reach 85% and is studied as a function of magnetic
field and initial temperature. The bosonic molecules remain trapped for 0.5 s
and their temperature is within a factor of 2 from the Bose-Einstein
condensation temperature. A thermodynamical model reproduces qualitatively the
experimental findings
A quasi-pure Bose-Einstein condensate immersed in a Fermi sea
We report the observation of co-existing Bose-Einstein condensate and Fermi
gas in a magnetic trap. With a very small fraction of thermal atoms, the 7Li
condensate is quasi-pure and in thermal contact with a 6Li Fermi gas. The
lowest common temperature is 0.28 muK = 0.2(1) T_C = 0.2(1) T_F where T_C is
the BEC critical temperature and T_F the Fermi temperature. Behaving as an
ideal gas in the radial trap dimension, the condensate is one-dimensional.Comment: 4 pages, 5 figure
Formation of a Matter-Wave Bright Soliton
We report the production of matter-wave solitons in an ultracold lithium 7
gas. The effective interaction between atoms in a Bose-Einstein condensate is
tuned with a Feshbach resonance from repulsive to attractive before release in
a one-dimensional optical waveguide. Propagation of the soliton without
dispersion over a macroscopic distance of 1.1 mm is observed. A simple
theoretical model explains the stability region of the soliton. These
matter-wave solitons open fascinating possibilities for future applications in
coherent atom optics, atom interferometry and atom transport.Comment: 11 pages, 5 figure
Experimental Study of the BEC-BCS Crossover Region in Lithium 6
We report Bose-Einstein condensation of weakly bound Limolecules in a
crossed optical trap near a Feshbach resonance. We measure a molecule-molecule
scattering length of nm at 770 G, in good agreement with
theory.We study the expansion of the cloud in the BEC-BCS crossoverregion.Comment: 4 pages, 3 figures, submitted to PR
Pure Gas of Optically Trapped Molecules Created from Fermionic Atoms
We report on the production of a pure sample of up to 3x10^5 optically
trapped molecules from a Fermi gas of 6Li atoms. The dimers are formed by
three-body recombination near a Feshbach resonance. For purification a
Stern-Gerlach selection technique is used that efficiently removes all trapped
atoms from the atom-molecule mixture. The behavior of the purified molecular
sample shows a striking dependence on the applied magnetic field. For very
weakly bound molecules near the Feshbach resonance, the gas exhibits a
remarkable stability with respect to collisional decay.Comment: 4 pages, 5 figure
Expansion of a lithium gas in the BEC-BCS crossover
We report on experiments in Li Fermi gases near Feshbach resonances. A
broad s-wave resonance is used to form a Bose-Einstein condensate of weakly
bound Li molecules in a crossed optical trap. The measured
molecule-molecule scattering length of nm at 770 G is found
in good agreement with theory. The expansion energy of the cloud in the BEC-BCS
crossover region is measured. Finally we discuss the properties of p-wave
Feshbach resonances observed near 200 Gauss and new s-wave resonances in the
heteronuclear Li- Li mixture.Comment: 10 pages, 3 figures, Proceedings of ICAP 200
Measurement of interaction energy near a Feshbach resonance in a 6Li Fermi gas
We investigate the strongly interacting regime in an optically trapped Li
Fermi mixture near a Feshbach resonance. The resonance is found at G
in good agreement with theory. Anisotropic expansion of the gas is interpreted
by collisional hydrodynamics. We observe an unexpected and large shift (G)
between the resonance peak and both the maximum of atom loss and the change of
sign of the interaction energy.Comment: 4 pages, 4 figure
Repulsively bound atom pairs in an optical lattice
Throughout physics, stable composite objects are usually formed via
attractive forces, which allow the constituents to lower their energy by
binding together. Repulsive forces separate particles in free space. However,
in a structured environment such as a periodic potential and in the absence of
dissipation, stable composite objects can exist even for repulsive
interactions. Here we report on the first observation of such an exotic bound
state, comprised of a pair of ultracold atoms in an optical lattice. Consistent
with our theoretical analysis, these repulsively bound pairs exhibit long
lifetimes, even under collisions with one another. Signatures of the pairs are
also recognised in the characteristic momentum distribution and through
spectroscopic measurements. There is no analogue in traditional condensed
matter systems of such repulsively bound pairs, due to the presence of strong
decay channels. These results exemplify on a new level the strong
correspondence between the optical lattice physics of ultracold bosonic atoms
and the Bose-Hubbard model, a correspondence which is vital for future
applications of these systems to the study of strongly correlated condensed
matter systems and to quantum information.Comment: 5 pages, 4 figure
New Directions in Degenerate Dipolar Molecules via Collective Association
We survey results on the creation of heteronuclear Fermi molecules by tuning
a degenerate Bose-Fermi mixture into the neighborhood of an association
resonance, either photoassociation or Feshbach, as well as the subsequent
prospects for Cooper-like pairing between atoms and molecules. In the simplest
case of only one molecular state, corresponding to either a Feshbach resonance
or one-color photoassociation, the system displays Rabi oscillations and rapid
adiabatic passage between a Bose-Fermi mixture of atoms and fermionic
molecules. For two-color photoassociation, the system admits stimulated Raman
adiabatic passage (STIRAP) from a Bose-Fermi mixture of atoms to stable Fermi
molecules, even in the presence of particle-particle interactions. By tailoring
the STIRAP sequence it is possible to deliberately convert only a fraction of
the initial atoms, leaving a finite fraction of bosons behind to induce
atom-molecule Cooper pairing via density fluctuations; unfortunately, this
enhancement is insufficient to achieve a superfluid transition with present
ultracold technology. We therefore propose the use of an association resonance
that converts atoms and diatomic molecules (dimers) into triatomic molecules
(trimers), which leads to a crossover from a Bose-Einstein condensate of
trimers to atom-dimer Cooper pairs. Because heteronuclear dimers may possess a
permanent electric dipole moment, this overall system presents an opportunity
to investigate novel microscopic physics.Comment: 10 pages, 5 figures, 77+ references, submitted to Euro. Phys. J.
topical issue on "Ultracold Polar Molecules: Formation and Collisions
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