Magnetic Dynamics and Nematic Phenomena in Spinor Antiferromagnetic Bose-Einstein Condensates
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Lao, Di
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Abstract
Magnetic and nematic phenomena are ubiquitous in nature such as the spontaneous magnetization of magnetite and the formation of liquid crystals. Ultracold atoms provide unique platforms for exploring multi-faceted quantum magnetic behavior associated with spin. The interplay between magnetic interaction and the interaction entangling spins and spatial motion (as known as spin-orbit coupling) gives rise to rich phase diagrams and phase transitions between different phases, which are ideal tools for understanding universal dynamics in the non-equilibrium system. Therefore in my work, we use sodium spinor Bose-Einstein condensates (BECs) to study two different aspects of nematic and magnetic phenomena, nematic-orbit coupling and magnetic solitons.
On one hand, complex Hamiltonians can be engineered in spinor BECs to simulate condensed matter physics, such as spin-orbit coupling. Spin-orbit coupling mechanism, a crucial element in the spin Hall effect, couples the atomic spins to the spatial degrees of freedom. As an analogy to spin-orbit coupling, a nematic-orbit coupling mechanism is proposed, which couples the spin-nematic tensors to the spatial motion of the atoms. To investigate the nematic-orbit coupling, we come up with an experimental proposal by using coplanar microwave arrays. And the phase diagram is carried out and two new striped phases are found theoretically. This opens a new realm for studying complex spin-nematic objects in spinor BECs.
On the other hand, a spinor BEC is a nonlinear magnetic system for defects to exist, such as vector solitons. A vector soliton is a type of solitary wave packet occurring in a nonlinear medium composed of multiple components. In our experiments, a new type of soliton called magnetic solitons is observed in a spinor BEC beyond the usual Manakov limit of the 1-dimensional Gross-Pitaevskii (GP) equations due to the magnetic interactions. By using a phase imprinting technique with magic wavelength, we created a pair of magnetic solitons in an antiferromagnetic spinor BEC. Besides, multiple solitons can be created by spatially modulating the pattern of the phase imprinting beams, which allows the future investigation of the bound state (Flemish strings), which turns out to be a potential candidate accounting for the universal dynamics of the non-equilibrium system generated after a quench from the polar phase to the antiferromagnetic phase of sodium BECs.
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2022-05-02
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Dissertation