We present the production of dual-species Bose-Einstein condensates (BECs) of
39K and
87Rb. Preparation of both species in the $\left|F=1,{m}_{F}=\ensuremath{-}1\right\ensuremath{\rangle}$ state enabled us to exploit a total of three Feshbach resonances, which allows for simultaneous Feshbach tuning of the
39K intraspecies and the $^{39}\mathrm{K}\text{\ensuremath{-}}^{87}\mathrm{Rb}$ interspecies scattering length. Thus dual-species Bose-Einstein condensates were produced by sympathetic cooling of
39K with
87Rb. A dark spontaneous force optical trap was used for
87Rb to reduce the losses in
39K due to light-assisted collisions in the optical trapping phase, which can be of benefit for other dual-species experiments. The tunability of the scattering length was used to perform precision spectroscopy of the interspecies Feshbach resonance located at 117.56(2) G and to determine the width of the resonance to 1.21(5) G by rethermalization measurements. The transition region from miscible to immiscible dual-species condensates was investigated and the interspecies background scattering length was determined to
28.5a0 using an empirical model. This paves the way for dual-species experiments with
39K and
87Rb BECs ranging from molecular physics to precision metrology.
This thesis describes the production of molecular Bose-Einstein condensates (BEC) of 6Li2 dimers and binding energy measurements of p-wave Feshbach molecules. A σ− Zeeman slower is used to produce a continuous beam of isotopically enriched 6Li atoms at speeds low enough to load a magneto-optical trap (MOT). We currently have a flux of slowed atoms of ~ 5 · 106 atoms/s loading the MOT with more than 108 atoms. We then transfer up to 106 atoms in an almost equal spin mixture of the two lowest hyperfine states into an optical dipole trap. We achieved condensates in three different crossed optical dipole trap geometries. The initial low power optical dipole trap was formed using light from a 25WVersaDisk Yb:YAG laser at 1030 nm. It consisted of a 15 W beam crossed with a 13 W beam at about 80 degrees with a waist of approximately 30 μm in each beam. By translating the focus of the second beam we could change the trap geometry from near symmetric to elongated. Nowadays, we produce condensates in a crossed dipole trap formed by a 100 W fibre laser. Both arms are focussed to a waist of 40 μm, cross each other at 14 degrees and have laser powers of ~80 W and ~70 W, respectively. Evaporative cooling is achieved by reducing the laser power near the broad s-wave Feshbach resonance at 834 G. By tuning to the low magnetic field side (770 G) of the Feshbach resonance molecules are formed through three-body recombination at sufficiently low temperatures. Further evaporation leads to the creation of a molecular BEC. After reducing the laser power by a factor of about 1000 in approximately 3 s we have observed more than 30 000 condensed molecules. During the evaporation the temperature decreases from about 100 μK to below 100 nK. We present measurements of the binding energies of 6Li p-wave Feshbach molecules formed in combinations of the |F = 1/2,mF = +1/2i (|1i) and |F = 1/2,mF = −1/2i (|2i) states. The binding energies scale linearly with magnetic field detuning for all three resonances. The relative molecular magnetic moments are found to be 113 ± 7 μK/G, 111 ± 6 μK/G and 118 ± 8 μK/G for the |1i − |1i, |1i − |2i and |2i − |2i resonances, respectively, in good agreement with theoretical predictions.