The study of BEC in weakly interacting system holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles, and may advance present understanding of superconductivity and superfluidity. By employing several new experimental techniques, the dark SPOT trap, rf induced evaporation, and the optically plugged magnetic trap, the authors were able to observe BEC in a gas of sodium atoms. The striking signature of Bose condensation was the sudden appearance of a bimodal velocity distribution below the critical temperature of {approximately} 2 {mu}K. The distribution consisted of an isotropic thermal distribution and an elliptical core attributed to the expansion of a dense condensate. Condensates contained up to 5 x 10{sup 5} atoms at densities exceeding 10{sup 14} cm{sup {minus}3}. Such high densities are unprecedented in cold atomic gases and open up new possibilities for studying a weakly interacting Bose gas over a broad range of densities and therefore strengths of interaction.
An ultracold Bose-Fermi gas mixture of 40K and 87Rb atoms has tunable interspecies interactions and therefore provides a fantastic platform for exploring not only few-body physics such as Feshbach molecule formation and Efimov trimers, but also many-body physics including Bose polarons, quantum Hall physics and so on. In this thesis, I present experimental evidence of Bose polarons in cold atoms obtained using radio-frequency spectroscopy to measure the excitation spectrum of fermionic 40K impurities resonantly interacting with a BEC of 87Rb atoms. These Bose polarons originate from the dressing of an impurity coupled to its environment, which is an important paradigm in quantum many-body physics. I also present initial work that launches an exciting new direction for our experiment, which is exploring rotating quantum gases. Goals for this work include studying both rotating Bose and Fermi superfluids with tunable interactions as well as working toward rapidly rotating quantum gases in the quantum Hall regime. For these goals, a new all-optical trap for rotating gases was designed, implemented, and tested using a 87Rb Bose-Einstein condensate.