Effects of Mean-Field Interactions and Raman-Induced Spin-Orbit Coupling in Bose-Einstein Condensates

Md Kamrul Hoque Ome

doi:10.7273/000005200

The experimental realization of dilute-gas Bose-Einstein condensates (BECs) has established an extremely versatile and powerful platform for exploring uncharted territories of modern physics. The dynamics of a BEC are strongly influenced by mean-field interactions and can further be manipulated by external coupling schemes, such as Raman-induced spin-orbit coupling (SOC). This dissertation reports a series of experiments exploring the effects of mean-field interactions and additional couplings in new regimes. In the first set of experiments, the non-exponential tunneling of a BEC in an accelerating optical lattice is investigated. Mean-field interaction leads to loop formation at the Brillouin zone edges of the band structure, causing atomic tunneling to the excited states. The non-exponential nature of the tunneling is experimentally and theoretically confirmed. Next, a set of experiments is described where, instead of an optical lattice, a more intricate lattice structure is generated: a spin-dependent effective optical lattice called the Zeeman lattice. This lattice is created by the simultaneous application of SOC and an external radio frequency field. Lattice dynamics, such as Bloch oscillations, are studied, and band spectroscopy is performed. Furthermore, experimental evidence is provided supporting the restoration of Galilean symmetry in the lattice, even though SOC alone breaks this symmetry. Third, supplementing SOC with a weak optical lattice provides experimental access to an interesting stripe phase. Its excitation spectrum is experimentally probed in the weak anisotropic spin interaction regime. A pseudo-Nambu-Goldstone gap in the zero-momentum limit of the Bogoliubov spectrum is measured and characterized with respect to the lattice strength. An excellent agreement between experimental observations and theoretical predictions is found. Finally, an alternative, independent way of generating structures and dynamics in a BEC is explored in the form of dark-antidark (DAD) solitons. A microwave drive is used to couple two hyperfine states of the ground state, and a spatially varying Rabi winding is employed. The mean-field dynamics cause DAD array formation during time evolution. This dissertation showcases the richness of the dynamics observable with BECs and opens the door to further advanced explorations with close connections to atomic physics, condensed matter physics, nonlinear science, and dispersive hydrodynamics.

Effects of Mean-Field Interactions and Raman-Induced Spin-Orbit Coupling in Bose-Einstein Condensates

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