A quantum gas apparatus for ultracold mixtures of K and Cs

-Since the first observation of Bose-Einstein condensation, the field of matter wave optics has progressed enormously and quantum degenerate mixtures of atoms have received special theoretical and experimental attention due to a variety of experiments not possible with single-species experiments. This thesis presents the setup of a new quantum gas apparatus for ultracold mixtures of K and Cs atoms with the capability of producing ultracold samples of KCs ground-state molecules. We describe the experimental apparatus and demonstrate its capabilities by producing Bose-Einstein condensates of 39K and 133Cs. The condensates are created independently without relying on sympathetic cooling. We introduce a sequential scheme that allows to mix degenerate samples of both species in an optical lattice. Our approach is universal and applicable to other species combinations when the two species show dramatically different behavior in terms of loss mechanisms and post laser cooling temperatures, i.e. species combinations that make parallel generation of quantum degenerate samples challenging. The preparation of heteronuclear molecules relies on precise knowledge of the interspecies scattering properties. We perform Feshbach spectroscopy for three different 39K-133Cs spin mixtures. We observe Feshbach resonances as joint atom loss and heating and improve the K-Cs interaction potentials to reproduce the resonance positions. The results open up the possibility to precisely tune the interspecies interaction and to associate free atoms to KCs molecules. We report on a first realization of sub-Doppler laser cooling of 39K atoms by employing degenerate three-dimensional Raman sideband cooling. The scheme takes advantage of the well-resolved excited hyperfine states on the D1 optical transition and results in a spin polarized sample with 1.4 x 10 8 atoms at temperatures of 1.8 K and with phase-space densities 10 (-4). The laser cooling scheme presented can be extended to far off-resonant lattice configurations and allows us to simplify existing high-resolution imaging techniques. Sets of different measurements present the latest results that have been obtained in the very end of this thesis work. We characterize the behavior of degenerate K and Cs samples loaded into a tunable lattice and a superlattice. We perform Kapitza-Dirac scattering to characterize the lattice depths and measure the period of a Bloch oscillation of K atoms confined in a 1D lattice. We show first results towards the production of a self-bound liquidlike droplet consisting of a K spin mixture. We also report on the ongoing work to create ground-state molecules and discuss home-built high-resolution objectives with single-site resolution.by Michael Gröbner, MSc. BSc.Kumulative Dissertation aus zwei ArtikelnIn den Artikeln ist 39 und 133 jeweils hochgestelltUniversity of Innsbruck, Dissertation, 2017OeBB(VLID)220271