Dynamics in an Ultracold Quantum Gas System for Mixtures
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Wang, Kaiyue
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Abstract
Ultracold gases of a mixture of species has drawn great interest in its prospective applications in quantum simulation. It is one step ahead of the traditional single-species ultracold systems with its complexities and its approaches to synthesize novel quantum matters. In particular, a mixture of bosons and fermion with large mass imbalance, along with artificial potentials such as optical lattices and box potentials, are anticipated to provide a versatile playground for mimicking the interactions between bosonic impurities and fermionic electrons transporting in solid states. This kind of system can provide insights into some questions and models that have been intriguing physicists for several decades, for example, the competing mechanisms of the Kondo screening and the RKKY interactions, explaining and predicting high-T_c superconductors, or even potentially providing new building blocks for quantum computers.
This thesis presents our work surrounding the construction and application of an experimental platform for ultracold gases mixtures of Cs-133 and Li-6. An important part of the work is to design and build a modular Cs atom source. The module features a multi-path, elongated 2D Magneto-Optical Trap (2D-MOT) for forming a concentrated atom stream to deliver the atoms into the science chamber. Bench tests and simulations are performed to understand and improve the module, which eventually provides a loading rate of up to 10E8 atoms/s. The thesis also reports the merging of the two existing systems, previously designated for each species, including installing the Cs source module, as well as laying out a complex optical system surrounding our science chamber that prepares the light required for manipulating the atoms of both species. To enable controlling each experiment cycle in the mixture platform through of a variety of signals, we have also developed a customizable modular control system as programmable signal sources. The control system can be operated from the desktop with a user-friendly interface, while it maintains sufficient performance and great extensibility fitting for our experiments. The system relies on a set of software and hardware protocols that has undergone several iterations and is being standardized.
This thesis also features the study of an intriguing dynamic process of Li_2 mBEC. The condensate is initially placed in an unstable point in a Floquet-engineered exotic dispersion, where it exhibits solitonic bifurcations in the momentum space. Through various experiments, numeric GPE simulations and discussions, we determine that the bifurcation trajectory can be understood semi-classically, while the solitonic behavior is related to the strong interactions. The work reveals possibilities for new types of solitons in higher dimensions, and provides possible solutions for preparing fermions in the ground state of an exotic dispersion through counter-diabatic processes, exploring the possible methods for realizing unconventional electronic pairings in a cold atom system.
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Date
2024-08-05
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Dissertation