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- Optical Control of Coherent Quantum Systems
- Optical control of coherent quantum systems has many methods and applications. In this defense we will discuss the effects of an electric field interacting with molecules with dipole moments. The theoretical study of such molecules will consist of two-level atom and a three-level atom in the λ configuration. The methods that will be discussed are population trapping using both bright and dark starts obtained by both STIRAP and CHIRAP pulses. The application to be discussed is how to create a room temperature maser.
- Investigating Accretion Mechanisms and Host Galaxy Environments of z~4 Quasars
- Observations of quasars at the highest accessible redshifts have revealed supermassive black holes (SMBHs) with masses much too massive to be accounted for by the growth mechanisms observed in the local universe. Masses up to 10 10 M ⊙ up to z~7 seem to suggest some type of secular evolution or external influence to feed the earliest SMBHs at extremely high rates. Observations at such redshifts come at expensive technical cost and require significant dedicated space-telescope observing time. However, in the z~4 regime, SMBHs are still relatively young, exhibit extreme growth rates, and are economically accessible for both frequent shallow snapshots as well as deep observations. In this dissertation, the accretion mechanisms of z~4 quasars and the structure of their host galaxies and nearby companions are investigated to search for evolution over cosmic time as well as outside influence on star formation rates (SFRs) and SMBH growth. Building the longest available X-ray light curves of four representative radio-quiet quasars, X-ray variability is evaluated at timescales from days to years in the rest frame, and robust simulations allow both qualitative and quantitate measurements of variability to compare with samples at lower redshifts. At all timescales, X-ray variability is consistent with or lower than lower-redshift samples and no evolution is observed. To investigate regions outside the central quasar, deep rest-frame UV observations of six similar quasars whose hosts exhibit highly varying SFRs are used to map the structure of star forming regions in the host galaxy and investigate the sky density of nearby sources. Despite the suggested hypothesis that major galactic mergers influence high SFRs, no evidence of merger scenarios is shown in the high-SFR sources, and the lower-SFR, which were thought to reside in sparse environments, also reside in dense environments.
- Ultrasonic Wave Propagation and Localization in a Nonreciprocal Phononic Crystal
- Ultrasonic wave propagation through a two-dimensional nonreciprocal phononic crystal with asymmetric aluminum rods in viscous water is studied for its application in Anderson localization and trapping of acoustic energy. A one-dimensional disorder in the otherwise 2D periodic crystal is introduced by disorienting the asymmetric rods along the rows and by keeping them equally oriented along the columns. An exponential decay of sound waves travelling along the direction of disorder is observed demonstrating Anderson localization whereas sound propagates as extended wave along the ordered direction. Localization length for the case of strong disorder with high randomness in the orientation of rods and weak disorder with weak fluctuations in the orientation of rods is evaluated. The degree of randomness in the orientation of the rods controls the localization length of the wave. Thouless's theoretical prediction for the scaling of Lyapunov exponent with disorder is experimentally observed for weak disorder at frequency in the transmission band and anomalous scaling is observed for band edge frequency. Transmission spectra of acoustic waves is also measured for opposite direction of propagation and nonreciprocity is observed for the exponentially weak transmission in the disordered direction as well as for extended states in the ordered direction. Breaking of reciprocity in the current structure is due to the broken PT symmetry. The T symmetry or the time reversal symmetry is broken by the viscous dissipation at the boundaries of scatterers and the water, and the P symmetry is broken by the asymmetric shape of the rods. Acoustic energy trapping inside a nonreciprocal phononic crystal cavity is studied by creating three configurations of cavities. These configurations are based on the orientation of the asymmetric scatterers on each side of the cavity. Only one of these configuration utilizes the nonreciprocal property of the structure. Enhancement of energy trapping in the cavity …
- Scaling, Power-Law First Return Times, and Non-Ergodicity
- This dissertation is a collection of papers on anomalous phenomena in physics, biology, and sociology. These phenomena are primarily analyzed in terms of their temporal and spatiotemporal statistical properties. The analysis is based on both numerical simulations and, in some cases, real-world physiological and sociological data. The primary methods of analysis are diffusion entropy analysis, power spectral analysis, multifractal analysis, and survival (or waiting-time) analysis.
- Developing Ultra-Fast Plasmonic Spiking Neuron via Integrated Photonics
- This research provides a proof of concept and background theory for the physics behind the state-of-the-art ultra-fast plasmonic spiking neurons (PSN), which can serve as a primary synaptic device for developing a platform for fast neural computing. Such a plasmonic-powered computing system allows localized AI with ultra-fast operation speed. The designed architecture for a plasmonic spiking neuron (PSN) presented in this thesis is a photonic integrated nanodevice consisting of two electro-optic and optoelectronic active components and works based on their coupling. The electro-optic active structure incorporated a periodic array of seeded quantum nanorods sandwiched between two electrodes and positioned at a near-field distance from the topmost metal layer of a sub-wavelength metal-oxide multilayer metamaterial. Three of the metal layers of the metamaterials form the active optoelectronic component. The device operates based on the coupling of the two active components through optical complex modes supported by the multilayer and switching between two of them. Both action and resting potentials occur through subsequent quantum and extraordinary photonics phenomena. These phenomena include the generation of plasmonic high-k complex modes, switching between the modes by enhanced quantum-confined stark effect, decay of the plasmonic excitations in each metal layer into hot-electrons, and collecting hot-electrons by the optoelectronic component. The underlying principles and functionality of the plasmonic spiking neuron are illustrated using computer simulation.
- Nonreciprocal and Non-Spreading Transmission of Acoustic Beams through Periodic Dissipative Structures
- Propagation of a Gaussian beam in a layered periodic structure is studied analytically, numerically, and experimentally. It is demonstrated that for a special set of parameters the acoustic beam propagates without diffraction spreading. This propagation is also accompanied by negative refraction of the direction of phase velocity of the Bloch wave. In the study of two-dimensional viscous phononic crystals with asymmetrical solid inclusions, it was discovered that acoustic transmission is nonreciprocal. The effect of nonreciprocity in a static viscous environment is due to broken PT symmetry of the system as a whole. The difference in transmission is caused by the asymmetrical transmission and dissipation. The asymmetrical transmission is caused solely by broken mirror symmetry and could appear even in a lossless system. Asymmetrical dissipation of sound is a time-irreversible phenomenon that arises only if both energy dissipation and broken parity symmetry are present in the system. The numerical results for both types of phononic crystals were verified experimentally. Proposed devices could be exploited as collimation, rectification, and isolation acoustic devices.
- Ionized Molecular Hydrogen Confinement Using Electron Space-Charge: A Plasma Trap
- An ion trap has been constructed that creates a potential well suitable for confining ions with the space charge of an electron cloud. The trap uses the concept of artificially structured boundaries, regions of overlapping electric and magnetic fields, to confine particles in a relatively field free volume. Measurements are presented from the build-up of ionized molecular hydrogen over time. Molecular hydrogen is introduced into the confinement volume by direct electron bombardment ionization of neutral background H2 leaked into the trap. Detailed analysis of the data is conducted using particle-in-cell simulations of trap operation and rate mechanics analysis. Pressure dependent estimates of ion lifetimes in the trap are on the order of milliseconds. Along with discussion of the trap a full introduction to the particle-in-cell technique is conducted through an original code implementation.
- Ongoing Developments on Continuum Solvation Models
- This work explores a continuum representation for diffuse layer models, thereby endowing continuum embedding models the ability to capture electrostatic phenomena in the environment such as the existence of electrolyte ions, and the nature of ionic liquids. It introduces a new field-aware continuum model that adjusts the size of the quantum regime per atom based on the distribution of charge in a system. The model accounts for the asymmetric nature of solvent distribution when applied to cations versus anions; it also overcomes the need to parameterize continuum interface models for different charged systems. The continuum representation of cavitation in water does not account for the tendency for water to form a hydrogen bonding network that is broken due to the formation of cavities. This effect is a major contributor to hydrophobic solvation and is an important precondition to the investigation of solvated proteins with continuum embedding. A new model inspired by machine learning advances is trained on molecular dynamics simulations due to the difficulty of isolating the cavitation energy term in experiment. Thermodynamic integration is used to calculate the energy from a step-like repulsive potential from cavities in TIP4P water, cavities ranging from small organic molecules, to small proteins. Predictions from this new model show a small improvement for small molecules and scale much better with respect to the size of the system.
- Band Theory and Beyond: Applications of Quantum Algorithms for Quantum Chemistry
- In the past two decades, myriad algorithms to elucidate the characteristics and dynamics of molecular systems have been developed for quantum computers. In this dissertation, we explore how these algorithms can be adapted to other fields, both to closely related subjects such as materials science, and more surprising subjects such as information theory. Special emphasis is placed on the Variational Quantum Eigensolver algorithm adapted to solve band structures of a periodic system; three distinct implementations are developed, each with its own advantages and disadvantages. We also see how unitary quantum circuits designed to model individual electron excitations within a molecule can be modified to prepare a quantum states strictly orthogonal to a space of known states, an important component to solve problems in thermodynamics and spectroscopy. Finally, we see how the core behavior in several quantum algorithms originally developed for quantum chemistry can be adapted to implement compressive sensing, a protocol in information theory for extrapolating large amounts of information from relatively few measurements. This body of work demonstrates that quantum algorithms developed to study molecules have immense interdisciplinary uses in fields as varied as materials science and information theory.
- Defect Modulated Properties of Molybdenum Disulfide Monolayer Films
- In this dissertation work, the study focuses on large areal growth of MoS2 monolayers and a study of the structural, optical and electrical properties of such monolayers before and after transfer using a polymer-lift off technique. This work will discuss the issue of contact resistance and the effect of defects (both intrinsic and extrinsic) on the overall quality of the monolayer films. The significance of this dissertation work is that a reproducible strategy for monolayer MoS2 film growth and quantification of areal coverage as well as the detrimental effects of processing on device performance is presented.
- Relaxation Time Approximations in PAOFLOW 2.0
- Electronic transport properties have been used to classify and characterize materials and describe their functionality. Recent surge in computational power has enabled computational modelling and accelerated theoretical studies to complement and accelerate experimental discovery of novel materials. This work looks at methods for theoretical calculations of electronic transport properties and addresses the limitations of a common approximation in the calculation of these properties, namely, the constant relaxation time approximation (CRTA). This work takes a look at the limitations of this approximation and introduces energy and temperature dependent relaxation times. This study is carried out on models and real systems and compared with experiments.