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Doctor of Philosophy with a Major in Physics
Doctor of Philosophy with a Major in Physics
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ItemDynamics in an Ultracold Quantum Gas System for Mixtures(Georgia Institute of Technology, 2024-08-05) Wang, KaiyueUltracold 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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ItemDevelopment of the Cherenkov Camera for the EUSO-SPB2 Mission and Analysis of Above-the-Limb Observations of Cosmic-Ray Particle Showers(Georgia Institute of Technology, 2024-07-30) Gazda, Eliza AnnaCosmic rays and neutrinos are particles that provide insights into high-energy events in the universe. These events take place beyond our Milky Way and have the power to accelerate charged particles to energies exceeding 1 ZeV. Detecting high-energy particles holds the key to understanding the distribution of gases and matter throughout the universe, the dynamics and laws governing the sources of these particles, and the particles themselves. These fundamental questions are subject to contemporary research, necessitating technological advancements for detecting and observing particles at increasingly higher energies. New methods and technologies improve detection sensitivity, and as detectors increase in size and efficiency, they collect more data. These data enable deeper insights into the phenomena driving cosmic-ray acceleration and propagation. Recent advancements in detectors and telescopes, such as the Telescope Array or the Pierre Auger Observatory, have led to numerous breakthroughs in detecting Ultra-High-Energy (UHE) particles, including cosmic rays and Very-High-Energy (VHE) gamma rays. These discoveries have enhanced our understanding of the origins and acceleration mechanisms of cosmic rays and the nature of astrophysical accelerators like supernova remnants and active galactic nuclei. They have also provided valuable insights into the environments where these processes take place. The detection of VHE gamma rays has enabled the investigation of extreme astrophysical phenomena such as gamma-ray bursts and pulsar wind nebulae, shedding light on high-energy processes and their impact on cosmic environments. These discoveries drive efforts for observatories like IceCube to detect UHE neutrinos. Neutrinos are neutral, weakly interacting particles capable of traveling vast distances through space without being absorbed or deflected by magnetic fields, offering direct information about their sources. The detection of UHE neutrinos could unveil the most energetic and distant astrophysical sources, including active galactic nuclei, gamma-ray bursts, and potentially undiscovered sources. This would provide a fresh perspective on the universe's most extreme environments and astrophysical processes, complementing the information obtained from cosmic rays and gamma rays. One method for studying UHE cosmic rays and UHE neutrinos is with a Cherenkov detector from a balloon, satellite, or high-altitude ground observatory. A telescope positioned at high altitudes above the Earth and pointed at the Earth's horizon can utilize the Earth as part of the detector. Particles interact within the Earth, leading to the observation of air showers. I designed, built, tested, and integrated a Cherenkov camera for the Extreme Universe Space Observatory (EUSO) on board the Super Pressure Balloon 2 (SPB2). My main contribution was to develop the camera front-end electronics and integrating the camera, thermal vacuum testing, and characterizing the performance of the camera in the field. Together with the rest of the team, we deployed the payload to fly as part of a NASA pathfinder mission. We operated the payload for two days before the balloon crash-landed in the Pacific. Despite the mission being cut short due to a balloon leak, we recorded air-shower data, validating the functionality of the design and the experiment. This data includes images of cosmic ray air showers within the energy range of 1PeV to 100PeV. This optical Cherenkov telescope was the first of its type to operate and successfully take data at such altitudes as a balloon payload. From the observed flight data, my primary objective was to analyze 45 minutes of data collected while we tilted the telescope above the horizon. The goal was to search for detected UHE cosmic ray air showers since pointing the instrument above the limb allows the detection of cosmic rays of energies above 1PeV, to 100PeV. I have developed techniques for calibrating, cleaning, and identifying UHE cosmic ray candidates. Initially, we studied the data to characterize our telescope's behavior and response. I contributed to developing calibration methods to flatfield our detector response and identify different types of noise events. Subsequently, I devised image-cleaning algorithms to differentiate between air shower images and events caused by the light fluctuations in the night sky background. For the analysis of this 45-minute period, I also established and executed a simulation chain to determine the UHE cosmic ray flux. The number of detected cosmic air showers matches flux predictions and verifies the performance of the telescope.
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ItemProbing Physics Beyond the Standard Model: Searching for ANITA Anomalous events with EUSO-SPB2(Georgia Institute of Technology, 2024-07-26) Romero Matamala, Oscar FernandoNeutrinos in the Very-High Energy (VHE) range (>10 PeV) and Ultra-High Energy (UHE) range (>EeV) have not been detected. In the past decade, multiple neutrino observatories have been proposed and developed. This has been driven by the discovery of astrophysical neutrinos by the IceCube Observatory and the potential identification of their sources. The Antarctic Impulsive Transient Antenna (ANITA) monitors the Antarctic ice in search of neutrinos using the Askaryan effect. During their 4th flight, they reported anomalous observations. The number of events consistent with upward-going extended air showers observed predicts a flux in tension with non-detection by IceCube, opening the possibility of Beyond Standard Model Physics. Using EUSO-SPB2, we attempt to follow up on these observations using an alternate channel: Cherenkov emission from extended air showers using the neutrino Earth skimming technique. This extends the observation of neutrinos at the VHE and UHE ranges, would enable exploring the most energetic processes in the Universe, testing the limits of the Standard Model, and potentially providing evidence related to the nature of Dark Matter.
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ItemDensity-Induced Spin-Nematic Squeezing in a Spin-1 Bose-Einstein Condensate(Georgia Institute of Technology, 2024-04-28) Barrios, MaryroseDensity or pressure modulation of materials is an important method for tuning and engineering interactions within materials studied in condensed matter systems. This tuning is often used to alter or modify the underlying properties of the material, leading to the crossing of a phase transition or enhanced chemical or mechanical properties. This thesis investigates the possibility of whether a similar approach might be employed in the study of ultracold atoms present within a spinor condensate. In our system we use the confining trap potential to modulate and increase the density of the system in such a way as to push the cloud of atoms from non-interacting to interacting, and across a quantum critical point. By crossing over into this new phase, we are able to perform a constant magnetic field quench to observe both spin mixing and spin-nematic squeezing. This allows us to achieve -8.4 ± 0.8 dB of squeezing and shows promise for future density-driven interactions.
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ItemUnraveling the Knot-so-Simple Behavior of Knitted Fabrics(Georgia Institute of Technology, 2024-04-27) Singal, KrishmaKnitted fabrics are a ubiquitous part of our day-to-day lives. Although we primarily interact with it through clothing, the programmable nature of knitted fabrics lends to its potential in a myriad of fields. Knitting is made by manipulating yarn, which is often inelastic, into a lattice of slipknots with emergent elastic properties. How the yarn is manipulated throughout the fabric, what stitches it forms and how they’re patterned, impacts the resultant fabric behavior under mechanical deformation. Traditionally, this elastic response of knitted fabrics is qualitatively determined, but this study works to systematically understand and quantify the programmable nature of knitted materials. We find that small scale changes in the topology of the yarn between stitches, the boundaries between stitches, have large scale impacts on the bulk fabric response. Not only on the stitch level, but the lengthscale of these boundaries further influences the fabric behavior. We probe the multi-scale behavior and application of knitting through several experimental studies: varying constituent yarn type composing the fabrics, comparing behaviors of classic periodic knitting patterns, exploring the impact of aperiodic patterned fabrics, and testing applications of knitting in biomimicry and biomechanics via known pattern composites.
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ItemDynamics and Transport in Strongly Correlated Quantum Magnets(Georgia Institute of Technology, 2024-04-24) Hakani, SamiThis dissertation discusses Raman dynamics and chiral orbital currents in strongly correlated quantum magnets. Such spin systems can host exotic quantum liquid phenomena including fractional excitations, emergent gauge fields, and novel particle statistics. In addition to broadening basic scientific knowledge, understanding the dynamics and transport of these magnetic systems can further technological applications in quantum computing and electronics. This is demonstrated by probing quantum liquid phenomena using Raman scattering on the spin-1/2 quantum liquid candidate Ba4Ir3O10. In a collaborative study, Raman scattering provides three signatures for fractional spinon excitations: (1) a broad spectral hump consistent with a continuum arising from 4-body scattering of Luttinger spinons, (2) strong phonon damping due to spin-phonon coupling due to spin-orbit interactions, and (3) the absence of (1) and (2) and the precipitation of magnetic order due to a 2% non-magnetic chemical substitution. Transport phenomena is studied in ferrimagnetic Mn3Si2Te6 which demonstrates colossal magnetoresistance in absence of magnetic polarization. In a second collaborative study, a crystallographic symmetry analysis demonstrates chiral orbital current patterns are consistent with experimental transport measurements. The demonstrated control of chiral orbital current enabled colossal magnetoresistance provides potential utility for future quantum technological applications. Finally, a novel effect in Raman dynamics is explored in the presence of crystalline topological defects. Even when such defects do not couple to the low energy Hamiltonian, it is shown that they can produce qualitatively new effects by coupling to electric field probes. Such effects rely on an underlying spinon liquid state, and they are not observed for magnetically ordered or gapped phases. Potential applications include using crystalline topological defects to modify response-theory operators independently of the Hamiltonian and thereby generate new probes of quantum phases.
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ItemModeling Ganymede's Interaction with the Jovian Magnetosphere: Ionospheric Outflow and the Juno PJ34 Flyby(Georgia Institute of Technology, 2024-04-04) Stahl, Aaron M.Using a hybrid model (kinetic ions, fluid electrons), we provide a three-dimensional model of Ganymede’s interaction with the Jovian magnetosphere and the moon’s ionospheric outflow. We also provide context for plasma and magnetic field observations from Juno's PJ34 flyby of Ganymede on 07 June 2021. Using five model configurations that successively increase the complexity of Ganymede’s atmosphere and ionosphere through the inclusion of additional particle species and ionization mechanisms, we examine the density and flow patterns of pick-up ions with small (H2+), intermediate (H2O+), and large (O2+) masses in Ganymede’s interaction region. The results are validated by comparing the modeled magnetic field and ion densities against time series from Juno’s magnetometer and plasma instruments. The major findings are: (a) Ganymede’s internal dipole dominated the magnetic field signature observed inside the moon’s magnetosphere, while plasma currents shaped the field perturbations within the “wake” region detected along the Jupiter-averted magnetopause. (b) Ganymede’s pick-up tail leaves a subtle, but clearly discernible imprint in the magnetic field downstream of the moon. (c) Heavy pick-up ions dominate ionospheric outflow and form a tail with steep outer boundaries. (d) During the Juno flyby, the position of Ganymede’s Jupiter-facing magnetopause varied in time due to Kelvin-Helmholtz waves traveling along the boundary layer. As such, the location of the Jupiter-facing magnetopause observed by Juno represents only a single snapshot of this time-dependent process. (e) Ionospheric hydrogen ions are partially generated outside of Ganymede’s magnetopause, forming a dilute H2+ corona that surrounds the moon’s magnetosphere. (f) Most H2O+ ions are produced at low latitudes where field lines are closed, resulting in a very dilute pick-up tail for this species.
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ItemExact coherent structures and non-universality in the direct cascade in two-dimensional turbulence(Georgia Institute of Technology, 2024-01-10) Zhigunov, DmitriyTurbulence is the most important problem in physics and applied mathematics, with applications ranging from astrophysics, to engineering, to plumbing, and more. Turbulent flows are often characterized by the presence of various cascades, which transport various quantities across length scales. This dissertation focuses on turbulence confined in two-dimensions, which has two cascades: an inverse (energy) cascade that moves energy towards increasingly larger scales, and a direct (enstrophy) cascade that moves the enstrophy towards smaller scales. The energy cascade leads to the formation of large-scale vortices, which often take up the largest length allowed by the domain. The first part of this dissertation flows focuses on the dynamics of these large scale vortices, where we find that these vortices behave for substantial time intervals like specific solutions of the Euler equation. These solutions are in many ways analogous to recurrent solutions of the Navier-Stokes equation which are often referred to as exact coherent structures. On the other hand, these solutions have a number of properties which distinguish them from their Navier-Stokes counterparts, such as the fact that they exist in continuous, multiparameter families. At the same time, the classical theory of the direct cascade by Kraichnan, Leith, and Batchelor fails to predict the proper scaling of the enstrophy spectrum found in numerical simulations and experiments. This discrepancy is often attributed to the presence of large-coherent vortices. We will provide a physically interpretable mechanism for the direct cascade that recovers KLB predictions in the absence of large-scale vortices, but leads to deviations in their presence. Finally, we return directly to the large-scale dynamics we explain in the first section, and investigate exactly how properties of the large-scale flow affect the scaling of the enstrophy spectrum.
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ItemAbstract and Physical Effects of Curvature on Dynamics of Extended Body Systems(Georgia Institute of Technology, 2023-12-07) Day, BrianThe presence of intrinsic curvature of an ambient space influences the dynamics of point particles moving through it as typically considered in applications of differential geometry in physical contexts, such as general relativity. We aim to utilize the mathematics of differential geometry to instead consider the collective curvature effects on extended body systems in some generic curved space. To this end we develop a mathematical framework which serves as the foundation of a general dynamics solver numerical toolkit in which users can simulate the dynamics of discrete extended body systems in generic curved spaces. Through analyzing the dynamics of such extended body systems we recognized a relationship between deformation of the body during its dynamics as a result of the ambient curvature. This led us to expand our mathematical model of extended bodies to include deformable bodies. We find that such deformable bodies can generate collective motion via deforming their body even in a ambient space lacking curvature. This is due to the presence of an abstract notion of curvature defined on the configuration space of the system via considering the system as being described by a mathematical object known as a fiber bundle. This revelation allows us to discuss the dynamics of such deformable control systems using the ideas of geometric mechanics. In particular, we consider recasting our system in a geometric mechanics framework to address the question of determining optimal controls of how to deform the system so as to minimize some cost function. This is based on considering the optimization problem as a variational problem whose solutions correspond to optimal controls of the system. We develop this variational approach into a numerical toolkit acting as the foundation of a more general purpose optimization toolkit for deformable control systems described by fibers bundles.
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ItemBiomolecules' conformational changes studied by simulations and enhanced sampling(Georgia Institute of Technology, 2023-11-17) Pang, Yui TikBiomolecules, ranging from small molecules like vitamins to proteins, play critical roles in sustaining cellular functions. Their functionality is closely tied to their ability to undergo conformational changes in response to environmental conditions or binding events. In drug design, understanding the conformational flexibility of small molecules is crucial. Small molecules can undergo conformational changes that affect their interactions with target proteins. This understanding is vital for predicting drug behavior and interactions in biological systems. Proteins, which are central to various biological processes, have intricate conformational dynamics. They can shift between various conformations to fulfill their functions, from subtle side chain rearrangements to extensive structural changes. Misfolded proteins can lead to diseases, making the study of protein conformational changes critical in both understanding biological processes and developing therapies. Molecular dynamics simulations offer a powerful tool for studying biomolecular dynamics. These simulations allow for precise control and measurement of various aspects of biomolecular systems, providing insights into their structural dynamics. However, some biological processes occur on long timescales, necessitating enhanced sampling techniques to accelerate simulations and capture rare events. In this thesis, we investigated three distinct biomolecular systems: capsid assembly modulator AT130, passenger domain of pertactin, and SARS-CoV-2 spike protein. Employing advanced simulation techniques and enhanced sampling methods, we delved into the intricate behaviors of these biomolecules, each representing a unique aspect of biological complexity. During this exploration, I also updated the open-source parameterization tool, Force Field Toolkit, to accommodate the novel sigma-hole particle (LP) introduced in CGenFF 4.0. Our research spanned a range of scales and complexities, showcasing the adaptability and relevance of simulations and enhanced sampling approaches in the study of diverse biological systems.