Physics and Astronomy, Department of
http://hdl.handle.net/2376/594
This community features research by faculty and students in the Department of Physics and Astronomy at Washington State University2021-06-16T08:22:13ZNonlinear dynamics and shock structures in elongated Bose-Einstein condensates
http://hdl.handle.net/2376/16756
Nonlinear dynamics and shock structures in elongated Bose-Einstein condensates
Dilute gas Bose-Einstein condensates are ultracold quantum gases that display many peculiar hydrodynamic properties, such as superfluidity, i.e. dissipation-less flow, a variety of solitonic textures and quantized vortex structures. Small amplitude excitations within a Bose-Einstein condensate are described by the Bogoliubov dispersion, and have been extensively studied in the past. This dissertation extends previous studies by focusing on strong, nonlinear excitations and shock structures generated in elongated Rb-87 Bose-Einstein condensates, elucidating novel dynamics in these quantum systems.
This dissertation is separated into two major parts. In the first part, the building and characterization of a new Bose-Einstein condensate apparatus at Washington State University is described. This apparatus has been built to generate ultracold clouds of Rb-87 and, more recently, K-41atoms. A description of the setups for both isotopes are provided. The apparatus reliably produces Bose-Einstein condensates of 7 x 10^5 Rb-87 atoms every 20 seconds.
In the second part of this dissertation, three experiments in a channel geometry are described that have been conducted with the new apparatus. In this part of the dissertation, quantum hydrodynamic properties are probed by using time-dependent optical potentials to generate nonlinear excitations and shock structures in an elongated Bose-Einstein condensate. An emergence of viscous-like shock dynamics, unidirectionality of a non-magnetic spin switch device, and the structure of dispersive shock waves in new types of higher order dispersions are observed. The work described in this dissertation establishes a novel platform for studying strong nonlinear effects in ultracold quantum gases.
2019-01-01T00:00:00ZA study of convex hull optimization and null-stream-based chi squared discrimination statistics for gravitational-wave signal analysis
http://hdl.handle.net/2376/16737
A study of convex hull optimization and null-stream-based chi squared discrimination statistics for gravitational-wave signal analysis
We develop data analysis methods to improve the sensitivity of searches for gravitational-wave signals from compact object binaries in networks of ground-based detectors, such as LIGO, Virgo and KAGRA. These are targeted for two different aspects of gravitational-wave data analysis. One focuses on blind searches in the sky, while the other improves the ability to veto triggers arising from spurious noise in detectors. The convex hull optimization focuses on maximizing the search statistic over the sky location parameters. This is done by bounding the search statistic by a convex function. This allows an all-sky search to effectively become a search over the convex set of detector data in the time delay parameter. We cut down on needed operations by searching the boundary (termed its convex hull) of this set of points, effectively searching over a smaller parameter space. We give the efficiency of such an algorithmic approach by comparing number of compute operations done to search the sky between current methods and our convex hull method. Our simulations show a gain in efficiency by a factor of seven or more, depending on the detector network used to perform a sky search. We also develop a veto for discriminating noise transients from compact binary coalescence signals. In some cases noise transients known as glitches match a signal search template well enough to generate a false trigger. We develop a network based statistic that distinguishes between gravitational-wave signal and noise triggers. This is done by combining a well known Chi-Squared statistic for single detectors with a null stream constructed veto for networks of detectors. The null stream is a linear combination of detector data constructed to remove any gravitational-wave signal content from it, leaving only detector noise. We then use this construction to compare data to signal template over smaller frequency windows in the detector band. Doing so allows for a more accurate test on how well a template matches over a given frequency range. Using simulated data, we show support for our null stream based statistic to perform as well, or better, than previous vetoing methods.
2019-01-01T00:00:00ZNONLINEAR PHENOMENA AND STRIPE PHASES IN BOSE-EINSTEIN CONDENSATES
http://hdl.handle.net/2376/17860
NONLINEAR PHENOMENA AND STRIPE PHASES IN BOSE-EINSTEIN CONDENSATES
Dilute-gas Bose-Einstein condensates offer a versatile testbed for the investigation of quantum phenomena. On the mean-field level, these ultracold atomic systems are described by the Gross-Pitaevskii equation which captures the nonlinearities induced by particle interactions. The analytical simplicity of behavior in the linear regime, i.e. in the absence of interparticle interactions, allows for the study of novel particle dispersions, generation of solid-state analogues, and the construction of atom interferometers. Nonlinearities lead to the formation of additional features such as solitonic matter-waves and dispersion loops.
The first two studies in this dissertation investigate strongly nonlinear phenomena in 87Rb Bose-Einstein condensates. The inherently nonlinear matter-wave structures known as solitons have been previously realized in one- and two-component systems, Here, that work is extended to three-component systems where two new species of soliton are observed. The second study considers the effects of interactions in optical lattice systems. Nonlinear behavior in an optical lattice is generally avoided, especially in atom interferometry applications. When nonlinear behavior dominates over the optical lattice potential a novel band loop appears in the lowest band of the dispersion. In this dissertation, Rabi oscillations and Bloch oscillations are observed in condensates in weak optical lattices and the resultant non-adiabatic behavior is discussed.
In the final two studies, novel quantum phases are generated by combining spin-orbit (SO) coupling with a second coupling type. For instance, supplementing the SO-coupling with optical lattice assisted hopping between the minima of the SO-coupled dispersion leads to the generation of the SO-coupled stripe phase. This phase is closely related to a supersolid, an exotic state of matter which simultaneously possesses the properties of a superfluid and a crystalline solid. By instead adding a radio-frequency field that also couples two Zeeman sublevels, an emergent lattice is formed which can exhibit Galilean invariant Kapitza-Dirac scattering and Bloch oscillations. Both of these compound coupling schemes are discussed.
Thesis (Ph.D.), Physics, Washington State University
2019-01-01T00:00:00ZSpectroscopy of Defects in Gallium Oxide
http://hdl.handle.net/2376/17887
Spectroscopy of Defects in Gallium Oxide
β-Gallium oxide (β-Ga2O3) is a promising semiconductor for its potential as a material in the field of power electronics. Magnesium doping of Ga2O3 has been shown to create a semi-insulating material, which could be utilized in ultrahigh-power devices. The properties of iridium impurities in undoped, magnesium-doped, and calcium-doped gallium oxides were investigated with IR spectroscopy. In undoped and Ca-doped β-Ga2O3, IR peaks at 3313, 3450, and 3500 cm-1 are tentatively assigned to O–H bond stretching modes of IrH complexes. Hydrogen-annealed Ga2O3:Mg shows an IR peak at 3492 cm-1, and H-annealed Ga2O3: Ca shows an IR peak at 3441 cm-1¬. These are assigned to an O-H bond-stretching mode of a neutral MgH and CaH complex, respectively. Polarization experiments were used to place the O-H bond of the MgH complex in the a-c plane. Mg, Ca, and Fe doped samples show an Ir4+ electronic transition feature at 5148 cm 1. By measuring the strength of this feature versus photoexcitation, the Ir3+/4+ donor level was determined to lie 2.2-2.3 eV below the conduction band minimum, which matches theory. Ga2O3:Mg also has a range of sidebands between 5100 and 5200 cm-1, attributed to IrMg pairs. Polarized IR measurements were used to show that the 5148 cm-1 peak is anisotropic, weakest for light polarized along the c axis.
Thesis (Ph.D.), Physics, Washington State University
2019-01-01T00:00:00Z