| Notes: | Advisor: Cheng Chin.
Thesis (Ph.D.)--The University of Chicago, Division of the Physical Sciences, Department of Physics, 2011.
Dissertation Abstracts International, Volume: 72-12, Section: B, page: 7426.
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| Summary: | This thesis reports on in situ probing of two-dimensional (2D) quantum gases of 133Cs atoms with tunable inter-atomic interactions. With spatially resolved in situ density measurements, the experimental work described in this thesis presents detailed studies on local equilibrium properties, near-equilibrium fluctuations and correlations, and non-equilibrium transport in 2D samples prepared near the critical points of continuous phase transitions. Specifically, we investigated the Berezinskii-Kosterlitz-Thouless (BKT) superfluid transition in the bulk and the superfluid-to-Mott insulator transition in an optical lattice.
The enabling experimental techniques include a new vacuum chamber design which permits a large numerical aperture for high resolution microscopy, a new approach of implementing all-optical cooling of cesium atoms to Bose-Einstein condensation (BEC), and the fabrication of a novel 2D optical trap. In particular, a fast and runaway evaporative cooling is realized using a tilted optical potential, allowing the production of a large atom number BEC in only 2∼4 s. A novel two-dimensional "pancake"-like optical trap is subsequently employed to convert a BEC into a monolayer of 2D quantum gas. This trap can be smoothly transformed into a 2D square lattice potential, simulating the paradigmatic Bose-Hubbard model.
Using this 2D trapping potential, we realize the superfluid-to-Mott insulator quantum phase transition in two dimensions and report the direct observation of incompressible Mott-insulating domains in deep lattices. Investigations on dynamics across the superfluid-insulator transition are presented, in which we observed anomalously slow mass transport and statistical evolution, indicating prolonged global many-body time scales across the insulator quantum phase transition.
For weakly interacting 2D Bose gases without the 2D lattice potential, we report on the observation of universal scaling behaviors in samples prepared at different temperatures and various interaction strengths. We confirm the scale invariance due to the intrinsic scaling symmetry of 2D gases and the universality near the BKT superfluid transition. A growing density-density correlation in the BKT critical region was observed and analyzed, and the static structure factors were extracted.
The experimental schemes and analysis methods we developed in this thesis to determine the universal scaling behaviors, fluctuations, correlations, and transport properties can be applied to other strongly correlated many-body atomic systems near a continuous phase transition. They form an important set of tools for our future objectives to study both the static and dynamic properties of quantum critical gases in optical lattices.
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