504 research outputs found
Magnetic field control of elastic scattering in a cold gas of fermionic lithium atoms
We study elastic collisions in an optically trapped spin mixture of fermionic
lithium atoms in the presence of magnetic fields up to 1.5kG by measuring
evaporative loss. Our experiments confirm the expected magnetic tunability of
the scattering length by showing the main features of elastic scattering
according to recent calculations. We measure the zero crossing of the
scattering length that is associated with a predicted Feshbach resonance at
530(3)G. Beyond the resonance we observe the expected large cross section in
the triplet scattering regime
Observation of the Pairing Gap in a Strongly Interacting Fermi Gas
We study fermionic pairing in an ultracold two-component gas of Li atoms
by observing an energy gap in the radio-frequency excitation spectra. With
control of the two-body interactions via a Feshbach resonance we demonstrate
the dependence of the pairing gap on coupling strength, temperature, and Fermi
energy. The appearance of an energy gap with moderate evaporative cooling
suggests that our full evaporation brings the strongly interacting system deep
into a superfluid state.Comment: 18 pages, 3 figure
Endpoint thermodynamics of an atomic Fermi gas subject to a Feshbach resonance
The entropy and kinetic, potential, and interaction energies of an atomic
Fermi gas in a trap are studied under the assumption of thermal equilibrium for
finite temperature. A Feshbach resonance can cause the fermions to pair into
diatomic molecules. The entropy and energies of mixtures of such molecules with
unpaired atoms are calculated, in relation to recent experiments on molecular
Bose-Einstein condensates produced in this manner. It is shown that, starting
with a Fermi gas of temperature , where is the
non-interacting Fermi temperature, an extremely cold degenerate Fermi gas of
temperature may be produced without further evaporative
cooling. This requires adiabatic passage of the resonance, subsequent sudden
removal of unpaired atoms, and adiabatic return. We also calculate the ratio of
the interaction energy to the kinetic energy, a straightforward experimental
signal which may be used to determine the temperature of the atoms and indicate
condensation of the molecules.Comment: 12 pages, 5 figure
Exploring the BEC-BCS Crossover with an Ultracold Gas of Li Atoms
We present an overview of our recent measurements on the crossover from a
Bose-Einstein condensate of molecules to a Bardeen-Cooper-Schrieffer
superfluid. The experiments are performed on a two-component spin-mixture of
Li atoms, where a Fesh\-bach resonance serves as the experimental key to
tune the s-wave scattering length and thus to explore the various interaction
regimes. In the BEC-BCS crossover, we have characterized the interaction energy
by measuring the size of the trapped gas, we have studied collective excitation
modes, and we have observed the pairing gap. Our observations provide strong
evidence for superfluidity in the strongly interacting Fermi gas.Comment: Proceedings of ICAP-2004 (Rio de Janeiro). Review on Innsbruck
BEC-BCS crossover experiments with updated Feshbach resonance positio
Collisional stability of a three-component degenerate Fermi gas
We report on the creation of a degenerate Fermi gas consisting of a balanced
mixture of atoms in three different hyperfine states of Li. This new system
consists of three distinguishable Fermions with different and tunable
interparticle scattering lengths , and . We are able
to prepare samples containing atoms in each state at a
temperature of about nK, which corresponds to . We
investigated the collisional stability of the gas for magnetic fields between 0
and 600 G and found a prominent loss feature at 130 G. From lifetime
measurements we determined three-body loss coefficients, which vary over nearly
three orders of magnitude
Efficient and robust initialization of a qubit register with fermionic atoms
We show that fermionic atoms have crucial advantages over bosonic atoms in
terms of loading in optical lattices for use as a possible quantum computation
device. After analyzing the change in the level structure of a non-uniform
confining potential as a periodic potential is superimposed to it, we show how
this structure combined with the Pauli principle and fermion degeneracy can be
exploited to create unit occupancy of the lattice sites with very high
efficiency.Comment: 4 pages, 3 figure
Antiferromagnetic Heisenberg Spin Chain of a Few Cold Atoms in a One-Dimensional Trap
We report on the deterministic preparation of antiferromagnetic Heisenberg
spin chains consisting of up to four fermionic atoms in a one-dimensional trap.
These chains are stabilized by strong repulsive interactions between the two
spin components without the need for an external periodic potential. We
independently characterize the spin configuration of the chains by measuring
the spin orientation of the outermost particle in the trap and by projecting
the spatial wave function of one spin component on single-particle trap levels.
Our results are in good agreement with a spin-chain model for fermionized
particles and with numerically exact diagonalizations of the full few-fermion
system
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