183 research outputs found
An apparatus for the production of molecular Bose-Einstein condensates
This thesis reports on the construction of an apparatus capable of producing a molecular Bose-Einstein-Condensate (BEC) of 6Li2. To create a condensate fermionic lithium is first evaporated in an oven, slowed by a Zeeman slower and captured in a magneto-optical-trap (MOT). A scheme for creating time-averaged arbitrary optical potentials for optimized transfer of the atoms from the MOT to a high-power, far detuned optical dipole trap was implemented, as well as magnetic field coils to tune the interactions of the atoms via Feshbach resonances. The first experiments with the new machine include the characterization of the optical dipole trap and evaporative cooling of 6Li
Efimov Physics in a three-component Fermi gas
This thesis reports on experiments studying the few-body physics of three distinguishable fermionic atoms with large scattering lengths. The experiments were performed with ultracold gases of fermionic 6Li atoms in three different hyperfine states. By tuning the strength of the interactions between the atoms with Feshbach resonances and measuring the rate constants for inelastic three-atom and atom-dimer collisions the intersections of two universal trimer states with the three-atom and atom-dimer continuum could be located. Subsequently, one of these Efimov states was directly observed with RF-association spectroscopy. Using this technique the binding energy of this Efimov state was measured as a function of the strength of the interparticle interactions. The experiments presented in this thesis provide a nearly complete understanding of the universal few-body physics of three-component Fermi gases of 6Li atoms. This understanding will be the foundation for future studies of the many-body physics of three-component Fermi gases
Detecting Friedel oscillations in ultracold Fermi gases
Investigating Friedel oscillations in ultracold gases would complement the
studies performed on solid state samples with scanning-tunneling microscopes.
In atomic quantum gases interactions and external potentials can be tuned
freely and the inherently slower dynamics allow to access non-equilibrium
dynamics following a potential or interaction quench. Here, we examine how
Friedel oscillations can be observed in current ultracold gas experiments under
realistic conditions. To this aim we numerically calculate the amplitude of the
Friedel oscillations which a potential barrier provokes in a 1D Fermi gas and
compare it to the expected atomic and photonic shot noise in a density
measurement. We find that to detect Friedel oscillations the signal from
several thousand one-dimensional systems has to be averaged. However, as up to
100 parallel one-dimensional systems can be prepared in a single run with
present experiments, averaging over about 100 images is sufficient.Comment: 5 pages, 4 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
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
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
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
Efimov Physics in a three-component Fermi gas
This thesis reports on experiments studying the few-body physics of three distinguishable fermionic atoms with large scattering lengths. The experiments were performed with ultracold gases of fermionic 6Li atoms in three different hyperfine states. By tuning the strength of the interactions between the atoms with Feshbach resonances and measuring the rate constants for inelastic three-atom and atom-dimer collisions the intersections of two universal trimer states with the three-atom and atom-dimer continuum could be located. Subsequently, one of these Efimov states was directly observed with RF-association spectroscopy. Using this technique the binding energy of this Efimov state was measured as a function of the strength of the interparticle interactions. The experiments presented in this thesis provide a nearly complete understanding of the universal few-body physics of three-component Fermi gases of 6Li atoms. This understanding will be the foundation for future studies of the many-body physics of three-component Fermi gases
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
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