Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Development of the Cold Atom Vacuum Standard(2023) Scherschligt, Julia; Porto, Trey; Rolston, Steven; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We describe the inception, design, development, and initial results of The Cold Atom Vacuum Standard (CAVS). It has been known for many years that vacuum level limits the lifetime of a cold atom cloud; we invert this to create a vacuum pressure measurement tool based on the trapped cloud lifetime. The difference between a standard and a sensor is of great concern to metrologists: a primary standard defines a unit, and a sensor transduces it. To have a device capable of both functions is to have a calibration-free measurement tool, which is of interest to many stakeholders in academia, industry, and defense. We describe all aspects of construction of the CAVS, including a lengthy investigation of vacuum technology. We ultimately demonstrate that the device is traceable to pressure through the fundamental physics of collision cross sections, thereby elevating it to status as not just a sensor, but a standard.Item Generation and Uses of Distributed Entanglement in Quantum Information(2019) Eldredge, Zachary David; Rolston, Steven L; Gorshkov, Alexey V; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this thesis, we focus on the questions of how quantum entanglement can be generated between two or more spatially separated systems and, once generated, how it can be applied in quantum technology. First we will discuss a protocol, which we conjecture to be optimal in some regimes, that quickly creates entangled states across long distances in systems with power-law interactions. We will discuss how this protocol compares with currently known bounds on entangled state generation and how it might be implemented in a three-dimensional lattice of Rydberg atoms. Next, we will turn our attention to more general questions of how the Lieb-Robinson bound and other limitations on entanglement can be used to inform the design of quantum computers. Quantum computers will be required to create entanglement if they are to realize significant advantages over classical computers, meaning that the generation of entanglement is an important question. First, we will discuss the implications of the Lieb-Robinson bound on graph descriptions of quantum computer architectures, and how the relevant graph parameter (diameter) compares to likely cost functions for architectures, such as maximum graph degree and total number of necessary connections. We will present a proposed graph architecture, the hierarchical product, which we believe provides excellent balance between these considerations. We will then introduce new methods of evaluating graphs that allow us to include quantum architectures capable of measurement and feedback operations. After doing so, we will show that the generation of entanglement entropy becomes a limit on computation. We will show that, for several possible physical models of computation, the generation of entanglement can be bounded by simple graph properties. We demonstrate a connection between worst-case scenarios for entanglement generation and a graph quantity called the Cheeger constant or isoperimetric number, which we evaluate for several proposed quantum computing architectures. Finally, we will look at the scenario of quantum sensing. In particular, we will examine protocols for quantum function estimation, where quantum sensors are available to measure all of the inputs to the function. We will demonstrate that entangled sensors are more capable than non-entangled ones by first deriving a new lower bound on measurement error and then presenting protocols that saturate these bounds. We will first do so for linear functions of the measured quantities and then extend this to general functions using a two-step linearizing protocol.Item Assessing 16S rRNA Marker-Gene Survey Measurement Process Using Mixtures of Environmental Samples(2018) Olson, Nathan D; Corrada Bravo, Héctor; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microbial communities play a fundamental role in environmental and human health. Targeted sequencing of the 16S rRNA gene, 16S rRNA marker-gene surveys, is used to measure and thus characterize these communities. The 16S rRNA marker- gene survey measurement process includes a number of molecular laboratory and computational steps. A rigorous measurement assessment framework can evaluate measurement method performance, in turn improving the validity of marker-gene survey study conclusions. In this dissertation, I present a novel framework and mixture dataset for assessing 16S rRNA marker-gene survey bioinformatic methods. Additionally, I developed software to facilitate working with 16S rRNA reference sequence databases and 16S rRNA marker-gene survey feature data. Computational steps, collectively referred to as bioinformatic pipelines, combine multiple algorithms to convert raw sequence data into a count table, which is subsequently used to test biological hypotheses. Algorithm choice and parameters can significantly impact pipeline results. The assessment framework and software developed for this dissertation improve upon existing assessment methods and can be used to evaluate new computational methods and optimize existing pipelines. Furthermore, the assessment framework presented here can be applied to other microbial community measurement methods such as shotgun metagenomics.Item Development of a display screen correlation metric for thermal imaging cameras(2007-05-11) Dinaburg, Joshua Benjamin; Jackson, Gregory; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Thermal imaging cameras detect infrared radiation to semi-quantitatively determine the thermal profile of the surroundings. Previously, no standard performance measurements have been established for thermal imaging cameras applications such as search and rescue and firefighting. The spatial contrast resolution in realistic atmospheric conditions was assessed through various full scale fires. Absorbing gas-phase combustion products greatly affected the ability of the TIC to measure local contrast in temperatures as a function of spatial frequency. A test was developed using a thermal gradient target to relate the voltage ramp output signal recorded in 8 bit digital tape format to the luminance projected by the LCD screen profile measured by a 16 bit CCD camera array with an IR filter. These relationship were nonlinear and unique to each imager tested. Measurements of the output signal only do not describe the final performance and a complete standard performance evaluation must measure the display luminance.