218 research outputs found
From Few to Many: Observing the Formation of a Fermi Sea One Atom at a Time
Knowing when a physical system has reached sufficient size for its
macroscopic properties to be well described by many-body theory is difficult.
We investigate the crossover from few to many-body physics by studying quasi
one-dimensional systems of ultracold atoms consisting of a single impurity
interacting with an increasing number of identical fermions. We measure the
interaction energy of such a system as a function of the number of majority
atoms for different strengths of the interparticle interaction. As we increase
the number of majority atoms one by one we observe the fast convergence of the
normalized interaction energy towards a many-body limit calculated for a single
impurity immersed in a Fermi sea of majority particles.Comment: 9 pages, 5 figure
Pairing in few-fermion systems with attractive interactions
We have studied quasi one-dimensional few-particle systems consisting of one
to six ultracold fermionic atoms in two different spin states with attractive
interactions. We probe the system by deforming the trapping potential and by
observing the tunneling of particles out of the trap. For even particle numbers
we observe a tunneling behavior which deviates from uncorrelated
single-particle tunneling indicating the existence of pair correlations in the
system. From the tunneling timescales we infer the differences in interaction
energies of systems with different number of particles which show a strong
odd-even effect, similar to the one observed for neutron separation experiments
in nuclei.Comment: 9 pages, 6 figure
Radio Frequency Association of Efimov Trimers
The quantum-mechanical three-body problem is one of the fundamental
challenges of few-body physics. When the two-body interactions become resonant,
an infinite series of universal three-body bound states is predicted to occur,
whose properties are determined by the strength of the two-body interactions.
We report on the association and direct observation of a trimer state
consisting of three distinguishable fermions using radio-frequency (RF)
spectroscopy. The measurements of its binding energy are consistent with
theoretical predictions which include non-universal corrections.Comment: 12 pages, 6 figure
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
Coherent molecule formation in anharmonic potentials near confinement-induced resonances
We perform a theoretical and experimental study of a system of two ultracold
atoms with tunable interaction in an elongated trapping potential. We show that
the coupling of center-of-mass and relative motion due to an anharmonicity of
the trapping potential leads to a coherent coupling of a state of an unbound
atom pair and a molecule with a center of mass excitation. By performing the
experiment with exactly two particles we exclude three-body losses and can
therefore directly observe coherent molecule formation. We find quantitative
agreement between our theory of inelastic confinement-induced resonances and
the experimental results. This shows that the effects of center-of-mass to
relative motion coupling can have a significant impact on the physics of
quasi-1D quantum systems.Comment: 7 pages, 4 figure
Fermionization of two distinguishable fermions
In this work we study a system of two distinguishable fermions in a 1D
harmonic potential. This system has the exceptional property that there is an
analytic solution for arbitrary values of the interparticle interaction. We
tune the interaction strength via a magnetic offset field and compare the
measured properties of the system to the theoretical prediction. At the point
where the interaction strength diverges, the energy and square of the wave
function for two distinguishable particles are the same as for a system of two
identical fermions. This is referred to as fermionization. We have observed
this phenomenon by directly comparing two distinguishable fermions with
diverging interaction strength with two identical fermions in the same
potential. We observe good agreement between experiment and theory. By adding
one or more particles our system can be used as a quantum simulator for more
complex few-body systems where no theoretical solution is available
Atom-Dimer Scattering in a Three-Component Fermi Gas
Ultracold gases of three distinguishable particles with large scattering
lengths are expected to show rich few-body physics related to the Efimov
effect. We have created three different mixtures of ultracold 6Li atoms and
weakly bound 6Li2 dimers consisting of atoms in three different hyperfine
states and studied their inelastic decay via atom-dimer collisions. We have
found resonant enhancement of the decay due to the crossing of Efimov-like
trimer states with the atom-dimer continuum in one mixture as well as minima of
the decay in another mixture, which we interpret as a suppression of exchange
reactions of the type |12>+|3> -> |23>+|1>. Such a suppression is caused by
interference between different decay paths and demonstrates the possiblity to
use Efimov physics to control the rate constants for molecular exchange
reactions in the ultracold regime.Comment: 5 pages, 3 figure
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