6 research outputs found
Observation of Feshbach resonances between two different atomic species
We have observed three Feshbach resonances in collisions between lithium-6
and sodium-23 atoms. The resonances were identified as narrow loss features
when the magnetic field was varied. The molecular states causing these
resonances have been identified, and additional lithium-sodium resonances are
predicted. These resonances will allow the study of degenerate Bose-Fermi
mixtures with adjustable interactions, and could be used to generate ultracold
heteronuclear molecules
Formation Time of a Fermion Pair Condensate
The formation time of a condensate of fermionic atom pairs close to a
Feshbach resonance was studied. This was done using a phase-shift method in
which the delayed response of the many-body system to a modulation of the
interaction strength was recorded. The observable was the fraction of condensed
molecules in the cloud after a rapid magnetic field ramp across the Feshbach
resonance. The measured response time was slow compared to the rapid ramp,
which provides final proof that the molecular condensates reflect the presence
of fermion pair condensates before the ramp.Comment: 5 pages, 4 figure
Observation of Bose-Einstein Condensation of Molecules
We have observed Bose-Einstein condensation of molecules. When a spin mixture
of fermionic Li-6 atoms was evaporatively cooled in an optical dipole trap near
a Feshbach resonance, the atomic gas was converted into Li_2 molecules. Below
600 nK, a Bose-Einstein condensate of up to 900,000 molecules was identified by
the sudden onset of a bimodal density distribution. This condensate realizes
the limit of tightly bound fermion pairs in the crossover between BCS
superfluidity and Bose-Einstein condensation.Comment: 4 pages, 3 figure
Condensation of Pairs of Fermionic Atoms Near a Feshbach Resonance
We have observed Bose-Einstein condensation of pairs of fermionic atoms in an
ultracold ^6Li gas at magnetic fields above a Feshbach resonance, where no
stable ^6Li_2 molecules would exist in vacuum. We accurately determined the
position of the resonance to be 822+-3 G. Molecular Bose-Einstein condensates
were detected after a fast magnetic field ramp, which transferred pairs of
atoms at close distances into bound molecules. Condensate fractions as high as
80% were obtained. The large condensate fractions are interpreted in terms of
pre-existing molecules which are quasi-stable even above the two-body Feshbach
resonance due to the presence of the degenerate Fermi gas.Comment: submitted to PRL. v3: clarifying revisions, added referenc
Feshbach Resonances in Fermionic Lithium-6
Feshbach resonances in lithium-6 were experimentally studied and
theoretically analyzed. In addition to two previously known s-wave resonances,
we found three p-wave resonances. Four of these resonances are narrow and yield
a precise value of the singlet scattering length, but do not allow us to
accurately predict the location of the broad resonance near 83 mT. Its position
was previously measured in a molecule-dissociation experiment for which we,
here, discuss systematic shifts
Diatomic molecules in ultracold Fermi gases - Novel composite bosons
We give a brief overview of recent studies of weakly bound homonuclear
molecules in ultracold two-component Fermi gases. It is emphasized that they
represent novel composite bosons, which exhibit features of Fermi statistics at
short intermolecular distances. In particular, Pauli exclusion principle for
identical fermionic atoms provides a strong suppression of collisional
relaxation of such molecules into deep bound states. We then analyze
heteronuclear molecules which are expected to be formed in mixtures of
different fermionic atoms. It is found how an increase in the mass ratio for
the constituent atoms changes the physics of collisional stability of such
molecules compared to the case of homonuclear ones. We discuss Bose-Einstein
condensation of these composite bosons and draw prospects for future studies.Comment: 10 pages, 5 figure