In this thesis, I present a novel experimental system and an optimal experimental scheme for an all-optical production of a sodium spinor Bose-Einstein condensate (BEC). With this scheme, I demonstrate that the number of atoms in a pure BEC can be greatly boosted by a factor of 5 over some widely used schemes in a simple single-beam or crossed-beam optical trap. Our scheme avoids technical challenges associated with some all-optical BEC methods and may be applicable to other optically trappable atomic species. I also discuss an upper limit for evaporative cooling efficiency in all-optical BEC approaches, and a good agreement between our theoretical model and experimental data.;In addition, we study the spin-mixing dynamics and phase diagrams of spinor BECs immersed in a microwave dressing field. Due to the interplay of spin-dependent interactions and the quadratic Zeeman energy induced by the microwave field, two types of quantum phase transitions are observed in our F=1 antiferromagnetic sodium spinor BEC system. We also demonstrate that many previously unexplored regions in the phase diagram of spinor condensates can be investigated by adiabatically tuning the microwave field across one of the observed quantum phase transitions. This method overcomes two major experimental challenges associated with some widely used methods, and is applicable to other atomic species. Agreements between our data and the mean-field theory for spinor Bose gases are also discussed.
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