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Singularity Resolution In Anisotropic And Black Hole Spacetimes In Loop Quantum Cosmology, Sahil Saini

LSU Doctoral Dissertations

Loop quantum cosmology (LQC) has in recent years led to successful resolution of singularities in cosmological models while agreeing with general relativity in low curvature limit. Existence of a bounce and the possibility of an effective continuum description closely approximating the quantum evolution have been notable features of this singularity resolution. The effective spacetimes of loop quantized isotropic and Bianchi-I models have been shown to be geodesically complete and free from strong singularities. In this dissertation, we extend these results to effective loop quantized Bianchi-II, Bianchi-IX and Kantowski--Sachs models with arbitrary minimally coupled matter, and also explore the possibility of …

The Effects Of Pressure And Magnetic Field On Phase Transitions And Related Physical Properties In Solid State Caloric Materials, Ahmad Ikhwan Us Saleheen

LSU Doctoral Dissertations

Solid-state caloric effects, such as the magnetocaloric (MCE) and barocaloric (BCE) effects, may be utilized in future cooling technologies that are more efficient and environment-friendly. Large caloric effects often occur near phase transitions, especially near coupled first-order magnetostructural transitions (MST), and are initiated by external parameters, such as magnetic field or hydrostatic pressure. In this dissertation, the effects of pressure, temperature, and magnetic field on the phase transitions in three material systems are studied in order to elucidate how the respective caloric effects are affected.

In the first study, the realization of a coupled MST in a MnNiSi-based system through …

Beam Theory For Classical And Quantum Nonlinear Optics---Exposing Classical And Quantum Correlations Of Transverse-Spatial Modes, Robert Nicholas Lanning

LSU Doctoral Dissertations

Optics is arguably the most important branch of physics that has ever been studied. It is not only an essential ingredient of many other branches of physics that we study, it governs how we see, how we measure, and how we communicate in the modern world. And as the world continues to change, so do our tools and resources. In a relatively short amount of time, we have progressed from rudimentary tools that shape the world around us, to tools that harness the fundamental laws of nature. Unsurprisingly, the laws of nature governing optics remain paramount. This is because many …

Bipartite Quantum Interactions: Entangling And Information Processing Abilities, Siddhartha Das

LSU Doctoral Dissertations

The aim of this thesis is to advance the theory behind quantum information processing tasks, by deriving fundamental limits on bipartite quantum interactions and dynamics. A bipartite quantum interaction corresponds to an underlying Hamiltonian that governs the physical transformation of a two-body open quantum system. Under such an interaction, the physical transformation of a bipartite quantum system is considered in the presence of a bath, which may be inaccessible to an observer. The goal is to determine entangling abilities of such arbitrary bipartite quantum interactions. Doing so provides fundamental limitations on information processing tasks, including entanglement distillation and secret key …

Theoretical Studies Of Ultrafast Electron Dynamics In Atoms And Molecules Via High-Order Harmonic Generation, Paul Vincent Abanador

LSU Doctoral Dissertations

The interaction of atoms and molecules with strong laser pulses is of fundamental interest in physics and chemistry. Notably, the process known as high-order harmonic generation (HHG) refers to the production of extreme-ultraviolet (XUV) light, which occurs when an ensemble of atoms or molecules is subjected to a strong infrared laser field. Characterized by an attosecond time scale (1 as = 10^-18 s), the HHG process provides the capability for experimental measurements to capture the ultrafast motion of electrons in these target atoms and molecules. The underlying physical mechanism behind this process naturally leaves imprints in the properties of …

Broadband Measurement And Reduction Of Quantum Radiation Pressure Noise In The Audio Band, Jonathan Daniel Cripe

LSU Doctoral Dissertations

One hundred years after Albert Einstein predicted the existence of gravitational waves in his general theory of relativity, the Laser Interferometer Gravitational-Wave Observatory (LIGO) made the first direct detection of gravitational waves. Since the first detection of gravitational waves from a binary black hole merger, LIGO has gone on to detect gravitational waves from multiple binary black hole mergers, and more recently from a binary neutron star merger in collaboration with telescopes around the world. The detection of gravitational waves has opened a new window to the universe and has launched the era of gravitational wave astronomy.

With the first …

Accelerated Broadband Spectra And Attosecond Charge Migration Simulations Using Real-Time Time-Dependent Density Functional Theory, Adam S. Bruner

LSU Doctoral Dissertations

In this dissertation, the calculations of light-matter interactions offer insight into the structure and dynamical response of electrons in molecular systems. Such information is useful for characterizing molecules, electronic structure, photochemistry, photomaterials, and a host of other applications. In the first part of this work, simulations of broadband absorption spectra are accelerated by the use of Pad´e approximanants of Fourier Transforms and dipole decomposition. Electronic absorption spectra from valence and core levels are obtained using time-dependent methods and compared to results from established perturbative techniques. In addition, core level absorption spectra are calculated for a nickel porphyrin and shown to …

Development Of A Slab-Based Monte Carlo Proton Dose Algorithm With A Robust Material-Dependent Nuclear Halo Model, John Wesley Chapman Jr

LSU Doctoral Dissertations

Pencil beam algorithms (PBAs) are often utilized for dose calculation in proton therapy treatment planning because they are fast and accurate under most conditions. However, as discussed in Chapman et al (2017), the accuracy of a PBA can be limited under certain conditions because of two major assumptions: (1) the central-axis semi-infinite slab approximation; and, (2) the lack of material dependence in the nuclear halo model. To address these limitations, we transported individual protons using a class II condensed history Monte Carlo and added a novel energy loss method that scaled the nuclear halo equation in water to arbitrary geometry. …

Endorectal Digital Prostate Tomosynthesis, Joseph Robert Steiner

LSU Doctoral Dissertations

Several areas of prostate cancer (PCa) management, such as imaging permanent brachytherapy implants or small, aggressive lesions, benefit from high image resolution. Current PCa imaging methods can have inadequate resolution for imaging these areas. Endorectal digital prostate tomosynthesis (endoDPT), an imaging method that combines an external x-ray source and an endorectal x-ray sensor, can produce three-dimensional images of the prostate region that have high image resolution compared to typical methods. This high resolution may improve PCa management and increase positive outcomes in affected men.

This dissertation presents the initial development of endoDPT, including system design, image quality assessment, and examples …

Entropic Bounds On Two-Way Assisted Secret-Key Agreement Capacities Of Quantum Channels, Noah Anthony Davis

LSU Doctoral Dissertations

In order to efficiently put quantum technologies into action, we must know the characteristics of the underlying quantum systems and effects. An interesting example is the use of the secret-key-agreement capacity of a quantum channel as a guide and measure for the implementation of quantum key distribution (QKD) and distributed quantum computation. We define the communication task of establishing a secret key over a quantum channel subject to an energy constraint on the input state and while allowing for unlimited local operations and classical communication (LOCC) between a sender and receiver. We then use the energy-constrained squashed entanglement to bound …