Tg Tiecke

Exploring an ultracold fermi-fermi mixture: Interspecies feshbach resonances and scattering properties of 6Li and 40K

We report on the observation of Feshbach resonances in an ultracold mixture of two fermionic species, (6)Li and (40)K. The experimental data are interpreted using a simple asymptotic bound state model and full coupled channels calculations. This unambiguously assigns the observed resonances in terms of various s- and p-wave molecular states and fully characterizes the ground-state scattering properties in any combination of spin states.

Bose-Einstein Condensation into Nonequilibrium States Studied by Condensate Focusing

We report the formation of Bose-Einstein condensates into nonequilibrium states. Our condensates are much longer than equilibrium condensates with the same number of atoms, show strong phase fluctuations, and have a dynamical evolution similar to that of quadrupole shape oscillations of regular condensates. The condensates emerge in elongated traps as the result of local thermalization when the nucleation time is short compared to the axial oscillation time. We introduce condensate focusing as a new method to extract the phase-coherence length of Bose-Einstein condensates.

Atom-dimer scattering and long-lived trimers in fermionic mixtures

We consider a heteronuclear fermionic mixture on the molecular side of an interspecies Feshbach resonance and discuss atom-dimer scattering properties in uniform space and in the presence of an external confining potential, restricting the system to a quasi-two-dimensional geometry. We find that there is a peculiar atom-dimer p-wave resonance which can be tuned by changing the frequency of the confinement. Our results have implications for the ongoing experiments on lithium-potassium mixtures, where this mechanism allows for switching the p-wave interaction between a K atom and Li-K dimer from attractive to repulsive, and forming a weakly bound trimer with unit angular momentum. We show that such trimers are long lived and the atom-dimer resonance does not enhance inelastic relaxation in the mixture, making it an outstanding candidate for studies of p-wave resonance effects in a many-body system.

Broad Feshbach resonance in the 6Li-40K mixture.

We study the widths of interspecies Feshbach resonances in a mixture of the fermionic quantum gases 6Li and 40K. We develop a model to calculate the width and position of all available Feshbach resonances for a system. Using the model, we select the optimal resonance to study the {6}Li/{40}K mixture. Experimentally, we obtain the asymmetric Fano line shape of the interspecies elastic cross section by measuring the distillation rate of 6Li atoms from a potassium-rich 6Li/{40}K mixture as a function of magnetic field. This provides us with the first experimental determination of the width of a resonance in this mixture, DeltaB=1.5(5) G. Our results offer good perspectives for the observation of universal crossover physics using this mass-imbalanced fermionic mixture.

Bose–Einstein condensation in a magnetic double-well potential

We present the first experimental realization of Bose–Einstein condensation in a purely magnetic double-well potential. This has been achieved by combining a static Ioffe–Pritchard trap with a time orbiting potential. The double trap can be rapidly switched to a single-harmonic trap of identical oscillation frequencies, thus accelerating the two condensates towards each other. Furthermore, we show that time-averaged potentials can be used as a means to control the radial confinement of the atoms. Manipulation of the radial confinement allows vortices and radial quadrupole oscillations to be excited.

Asymptotic-bound-state model for Feshbach resonances

We present an asymptotic-bound-state model which can be used to accurately describe all Feshbach resonance positions and widths in a two-body system. With this model we determine the coupled bound states of a particular two-body system. The model is based on analytic properties of the two-body Hamiltonian and on asymptotic properties of uncoupled bound states in the interaction potentials. In its most simple version, the only necessary parameters are the least bound state energies and actual potentials are not used. The complexity of the model can be stepwise increased by introducing threshold effects, multiple vibrational levels, and additional potential parameters. The model is extensively tested on the {sup 6}Li-{sup 40}K system and additional calculations on the {sup 40}K-{sup 87}Rb system are presented.

Feshbach resonances in 3He*-4He* mixtures

We discuss the stability of homonuclear and heteronuclear mixtures of

Feshbach resonances inHe3*-He4*mixtures

^{3}\mathrm{He}

Feshbach resonances in {sup 3}He*-{sup 4}He* mixtures

and

Search for broad Feshbach resonances un mixtures of fermionic quantun gases

^{4}\mathrm{He}