Quantum Physics Commons^™

Photon Counting Statistics Of Classical And Quantum Light Sources, Luis Felipe Morales Bultron

Graduate Theses and Dissertations

Multiple sources of light, including coherent light, thermal light, light from a degenerate parametric oscillation and resonance fluorescence from a two level coherently driven atom are considered for the analysis of their wait time statistics. We include the second order normalized correlation function and Mandel's Q parameter for brief discussion. A general framework to analyze the generalized conditional and unconditional wait time distributions is also obtained in order to understand the photo-count statistics of the light sources included in this work. Average and variance of wait times with respect to both unconditional and conditional wait time distribution are also obtained …

Gate-Controlled Quantum Dots In Two-Dimensional Tungsten Diselenide And One-Dimensional Tellurium Nanowires, Shiva Davari Dolatabadi

Graduate Theses and Dissertations

This work focuses on the investigation of gate-defined quantum dots in two-dimensional transition metal dichalcogenide tungsten diselenide (WSe2) as a means to unravel mesoscopic physical phenomena such as valley-contrasting physics in WSe2 flakes and its potential application as qubit, as well as realizing gate-controlled quantum dots based on elementaltellurium nanostructures which may unlock the topological nature of the host material carriers such as Weyl states in tellurium nanowires.The fabrication and characterization of gate-defined hole quantum dots in monolayer and bilayer WSe2 are reported. The gate electrodes in the device design are located above and below the WSe2 nanoflakes to accumulate …

Quantum Dots In Two-Dimensional Tungsten Diselenide, Jeb Allen Michael Stacy

Graduate Theses and Dissertations

This work focuses on the investigation of single and double quantum dots in two-dimensional transition metal dichalcogenide tungsten diselenide (WSe_2) as a means to evaluate the valley degree of freedom as a potential qubit and ambipolar tungsten diselenide monolayers as single photon sources. Gate-defined quantum dots in monolayer and bilayer WSe_2 were fabricated and characterized. Single dot devices are gated from above and below the WSe_2 to accumulate a hole gas. Temperature dependence of Coulomb-blockade peak height is consistent with single-level transport. Excited-state transport in the quantum dot is shown for both monolayer and bilayer devices. Magnetic field dependence of …

Quantum Transport And Electric-Field Effects In Layered Topological Semimetals And Magnetic Materials, Arash Fereidouni Ghaleh Minab

Graduate Theses and Dissertations

This dissertation describes transport experiments on quantum devices in layered Dirac nodal line topological semimetals and antiferromagnetic materials down to a few layers. We used gate-induced effects to alter the transport properties of these materials.

First, we introduced current annealing in topological semimetals to achieve high-quality devices. We demonstrate current annealing to substantially improve the electronic transport properties of 2D topological semimetal flakes. Contact resistance and resistivity were improved by factors up to 2,000,000 and 20,000, respectively, in devices based on exfoliated flakes of two topological semimetals, ZrSiSe and BaMnSb2. Using this method, carrier mobility in ZrSiSe improved by a …

Crystal Growth And Property Tuning Of Layered Magnetic Topological Semimetals, Krishna Pandey

Graduate Theses and Dissertations

The demand for energy-efficient devices has been growing rapidly due to the need for data-driven technologies and the global energy crisis. As device size approaches the atomic scale, the miniaturization of electronic devices may stop in the near future unless fundamentally new materials or device concepts are developed. The emergent topological materials with exotic properties show remarkable robustness against crystal lattice defects, which are promising for next-generation technology. These materials host exotic properties such as high mobility, large magnetoresistance, chiral anomaly, and surface Fermi arcs, etc. Among various topological materials, the ZrSiS-family materials exhibit two types of Dirac states, which …

Hybrid Two Dimensional Quantum Devices, Joshua Patrick Thompson

Graduate Theses and Dissertations

This thesis describes measurements on hybrid material systems involving two dimensional (2D) materials and phenomena along with the development of a small, hermetically sealed cell. The hermetic cell is designed to assist with analyzing sensitive 2D materials outside of an inert environment. When working with van der Waals materials that are especially sensitive to oxygen or water, it can be difficult to identify usable thin flakes without exposing them to air. To help preserve materials for analysis in air, a capsule was designed that isolates the material in an inert environment. Although the capsule is hermetically sealed, the encapsulated material …

Quantum Dynamical Phenomena In Non-Hermitian And Magnomechanical Systems, Saeid Vashahri Ghamsari

Graduate Theses and Dissertations

In this dissertation, we have investigated quantum dynamics via three case studies. First, we studied a system of two coupled waveguides respectively carrying optical damping and optical gain in addition to squeezing elements in one or both waveguides. Such a system is expected to generate highly entangled light fields in the two waveguides. We, however, show that the degree of the created entanglement is significantly affected by the quantum noises associated with the amplification and dissipation. Because of the noise effect, one can only have nonzero entanglement for a limited time interval. Second, we generalized the first project by considering …

Designing Cryogenic Strain Device For 2d Materials, Jake Carter

Mechanical Engineering Undergraduate Honors Theses

The Churchill lab working within the Physics Department at the University of Arkansas is working to create important quantum states including weak topological insulators (TIs) through the use of symmetry engineering and topological electronic states in two-dimensional (2D) crystals of WHM materials. Experimental results of these topological states have been obstructed due to the difficulty to perform controlled in situ strain. This project strives to create a mount to utilize a piezoelectric nanopositioner within cryostats achieving an in situ strain that creates the quantum states the lab is looking to observe. This report also examines the necessary equations to determine …

Optical Properties Of Ultrathin In(Ga)As/Gaas And In(Ga)N/Gan Quantum Wells, Yurii Maidaniuk

Graduate Theses and Dissertations

Recently, structures based on ultrathin quantum wells (QWs) began to play a critical role in modern devices, such as lasers, solar cells, infrared photodetectors, and light-emitting diodes. However, due to the lack of understanding of the formation mechanism of ultrathin QWs during the capping process, scientists and engineers cannot fully explore the potential of such structures. This study aims to investigate how structural parameters of ultrathin QWs affect their emission properties by conducting a systematic analysis of the optical properties of In(Ga)As/GaAs and In(Ga)N/GaN ultrathin QWs. Specifically, the analysis involved photoluminescence measurements combined with effective bandgap simulation, x-ray diffraction, and …

An Update On The Computational Theory Of Hamiltonian Period Functions, Bradley Joseph Klee

Graduate Theses and Dissertations

Lately, state-of-the-art calculation in both physics and mathematics has expanded to include the field of symbolic computing. The technical content of this dissertation centers on a few Creative Telescoping algorithms of our own design (Mathematica implementations are given as a supplement). These algorithms automate analysis of integral period functions at a level of difficulty and detail far beyond what is possible using only pencil and paper (unless, perhaps, you happen to have savant-level mental acuity). We can then optimize analysis in classical physics by using the algorithms to calculate Hamiltonian period functions as solutions to ordinary differential equations. The simple …

A Study Of Optical Nonlinearities At The Single-Photon Level For Quantum Logic, Balakrishnan Viswanathan

Graduate Theses and Dissertations

In this dissertation, we shall focus on theoretically studying quantum nonlinear optical schemes to construct a conditional phase gate at the single-photon level. With an aim to develop analytical models, we shall carry out a rigorous quantized multimode field analysis of some of these schemes involving only the interacting field operators. More specifically, we shall first study the three-wave mixing process involving two single-photons in a second-order nonlinear medium (x(2)) under two different cases viz. when the photons are traveling with equal velocities and when they are traveling with different velocities, and explore the possibility of using them for building …

Acoustics To Quantum Materials: A Centennial History Of The Department Of Physics, University Of Arkansas, Rajendra Gupta, Paul C. Sharrah

Physics Faculty Publications and Presentations

The department of physics at the University of Arkansas was established in the 1907-08 academic year, although physics was taught from the very start of the University in 1872. The department celebrated its centennial in 2007-2008. Acoustics to Quantum Materials is a centennial history of the department covering the period 1907-08 to 2007-08. While the emphasis is on this period, instruction of physics over the period 1872-1907 is covered in two prologues, and the period 2009-18 is briefly covered in an epilogue. The first research laboratory to be established was in the area of acoustics. Subsequently, the department’s faculty have …

Theoretical Investigations Of The Electronic, Magnetic, And Thermoelectric Properties Of Transition-Metal Based Compounds, Haleoot Edaan Raad

Graduate Theses and Dissertations

The electronic, magnetic, and thermoelectric properties of transition-metal based compounds were investigated by using the density functional theory and Boltzmann transport formalism. It was found that the Co-based Heusler compounds and InSe monochalcogenide are among the materials that may be used for future thermoelectric devices. Furthermore, the investigation showed that the quaternary Heusler compounds, such as, CoFeYGe, where Y is Ti or Cr, are half-metallic ferromagnetic materials with full electron spin polarization. The lattice thermal conductivity (κL) was found to decrease for these alloys as the temperature increases. The present investigation indicated that the phonon optical modes have a major …

Possible Schemes For A Single Photon Switch, Hemlin Swaran Rag

Graduate Theses and Dissertations

I consider the effectiveness of a single control photon to route a target photon using two processes: the first one uses the transient excitation of a two-level system and the second one which uses the permanent population transfer in a three-level Λ-system to route the target photon. In the absence of a single control photon and when the system has additional decay channels, I find ways to optimize the success probability of routing with an increasing number of photons in the control field.

Plasmonic Enhancement Of Photoluminescence And Photobrightening In Cdse Quantum Dots, David Alan French

Graduate Theses and Dissertations

Quantum dots are gaining recognition not just in the physics and chemistry community, but in the public eye as well. Quantum dot technologies are now being used in sensors, detectors, and even television displays. By exciting quantum dots with light or electricity, they can be made to emit light, and by altering the quantum dot characteristics the wavelength can be finely tuned. The light emitted can be also be made more intense by an increase in the excitation energy. The excitation light can be increased via plasmonic enhancement, leading to increased luminescence. Aside from the relatively steady-state response, quantum dots …

Scattering Of Few Photon Fields By Two Level Systems In A One Dimensional Geometry, William Konyk

Graduate Theses and Dissertations

Recent experimental progress has realized strong, efficient coupling of effective two level systems to waveguides. We study the scattering of multimode photons from such emitters coupled losslessly to the confined geometry of a one dimensional waveguide. We develop novel techniques for describing the scattered state of both single and multi-photon wavepackets and explore how such wavepackets interact with arrays of emitters coupled to a one dimensional waveguide. Finally, we apply these techniques and analyze the capability of two particular systems to act as a quantum conditional logic gate.

Discord And Global Discord In Systems Of Coupled Quantum Dots In Driven Cavities With Dissipation, And A Method For The Calculation Of Global Discord, Willa Danielle Rawlinson

Graduate Theses and Dissertations

In the field of quantum information, which is subdivided into quantum computing and quantum cryptography, quantum correlations are essential for a performance or security boost not achievable with classical means. Various quantum correlation measures exist for evaluating a state’s potential to be a qubit (quantum bit). Entanglement, or nonseparability of quantum states, is the older, better known class of measures. However, for a mixed state, quantum entanglement is an incomplete measure of quantumness. Quantum discord, and its multibody extension global discord, encompass all quantum correlations. We study systems of coupled quantum dots using these measures.

We study the discord of …

Interactive Physics And Characteristics Of Photons And Photoelectrons In Hyperbranched Zinc Oxide Nanostructures, Garrett Edward Torix

Graduate Theses and Dissertations

As is commonly known, the world is full of technological wonders, where a multitude of electronic devices and instruments continuously help push the boundaries of scientific knowledge and discovery. These new devices and instruments of science must be utilized at peak efficiency in order to benefit humanity with the most advanced scientific knowledge. In order to attain this level of efficiency, the materials which make up these electronics, or possibly more important, the fundamental characteristics of these materials, must be fully understood. The following research attempted to uncover the properties and characteristics of a selected family of materials. Herein, zinc …

Static And Dynamical Properties Of Ferroelectrics And Related Material In Bulk And Nanostructure Forms, Zhigang Gui

Graduate Theses and Dissertations

Ferroelectrics (FE) and multiferroics (MFE) have attracted a lot of attentions due to their rich and novel properties. Studies towards FE and MFE are of both fundamental and technological importance. We use a first-principles-based effective Hamiltonian method, conventional ab-initio packages and linear-scale three-dimension fragment method to investigate several important issues about FE and MFE. Tuning the properties of FE and MFE films are essential for miniaturized device applications, which can be realized through epitaxial strain and growth direction. In this dissertation, we use the effective Hamiltonian method to study (i) BaTiO 3 films grown along the (110) pseudocubic direction on …

Mirror Buckling Transitions In Freestanding Graphene Membranes Induced Through Scanning Tunneling Microscopy, James Kevin Schoelz

Graduate Theses and Dissertations

Graphene has the ability to provide for a technological revolution. First isolated and characterized in 2004, this material shows promise in the field of flexible electronics. The electronic properties of graphene can be tuned by controlling the shape of the membrane. Of particular interest in this endeavor are the thermal ripples in graphene membranes. Years of theoretical work by such luminaries as Lev Landau, Rudolf Peierls, David Mermin and Herbert Wagner have established that 2D crystals should not be thermodynamically stable. Experimental research on thin films has supported this finding. Yet graphene exists, and freestanding graphene films have been grown …

The Role Of Quantum Dot Size On The Performance Of Intermediate Band Solar Cells, Najla Alnami

Graduate Theses and Dissertations

The goal of this thesis is to understand possible mechanisms for the reported decrease of the open circuit voltage and solar cell efficiency in quantum dot (QD) intermediate band solar cells (IBSCs). More specifically, the effect of indium arsenide (InAs) QD height on the open circuit voltage and solar cell efficiency was studied in a systematic way. To explore this effect in QD solar cells, several solar cells (SCs) were grown with varying InAs QD heights. All experimental characteristics of the QD solar cells were compared to a reference structure without QDs. All samples were grown by Molecular Beam Epitaxy …

From Graphite To Graphene Via Scanning Tunneling Microscopy, Dejun Qi

Graduate Theses and Dissertations

The primary objective of this dissertation is to study both graphene on graphite and pristine freestanding grapheme using scanning tunneling microscopy (STM) and density functional theory (DFT) simulation technique. In the experiment part, good quality tungsten metalic tips for experiment were fabricated using our newly developed tip making setup. Then a series of measurements using a technique called electrostatic-manipulation scanning tunneling microscopy (EM-STM) of our own development were performed on a highly oriented pyrolytic graphite (HOPG) surface. The electrostatic interaction between the STM tip and the sample can be tuned to produce both reversible and irreversible large-scale movement of the …

Quantum Resonant Beats And Revivals In The Morse Oscillators And Rotors, Zhenhua Li

Graduate Theses and Dissertations

Analytical eigenfunctions and eigenvalues for the Morse oscillator were applied to investigate the quantum resonant beats and revivals of wave packet propagation. A concise way for exact prediction of the complete revival period of the Morse oscillator was given for the first time. It was suggested that any complete period was made of integer numbers of the minimum or fundamental period. Within the fundamental period, the anharmonicity of this oscillator appeared to cause interesting space-time phenomena that include relatively simple Farey-sum revival structures. In addition, a simple sum of two Morse oscillators led to a double-Morse well whose geometric symmetry …

Phase Control In Atomic Coherence, Utsab Khadka

Graduate Theses and Dissertations

In this thesis, atomic coherence is used to enhance nonlinear optical processes in multi-level atoms. The multi-photon transitions are driven resonantly, and at the same time without absorptive losses, by using electromagnetically induced transparency (EIT), thereby allowing the study of χ⁽³⁾ and χ⁽⁵⁾ nonlinearities using weak driving fields. The coherently modified probe beam(s) and the atom-radiated signal fields arising from four- and six- wave- mixing (FWM and SWM) processes are measured in the spectral, temporal and spatial domains.

In a three-level ladder-type atomic system, multiple peaks having spectral asymmetries are observed in the EIT window as well as …

Investigation Of Negative Differential Resistance Phenomena In Quantum Well Heterostructures, Nazariy Andrushchak

Graduate Theses and Dissertations

Increasing interest in entirely new possibilities for quantum mechanical description of carriers transport is becoming more evident with the developing advancements in epitaxial growth technique. Consequently, molecular beam epitaxy (MBE) technique is considered to be the most precise technique that allows the growth of ultra-thin layers of different compositions.

Those structures can be designed to investigate the wave-nature of carriers, which broadens the possibilities in device design and fabrication for a specific area. In this thesis the fundamental study of the real space charge transfer (RST) mechanism that took place in quantum well heterostructures and led to the negative differential …

Study Of Nanoidentation And Tip Geometry In Gaas (100) At Ultra-Low-Loads For The Patterning Of Quantum Dots, Robin Prince

Inquiry: The University of Arkansas Undergraduate Research Journal

In this study, nanoindentations were produced and characterized for the future patterning of quantum dots. Nanoindentation was performed on a Si-doped (n-type) Vertical Gradient Freeze (VGF) GaAs (100) wafer with a 700 nm GaAs (100) layer grown by molecular beam epitaxy (MBE). Nanoindentation was performed with a Berkovich diamond tip, a cube corner diamond tip, and a 600 conical diamond tip. Nanoindentation of GaAs has been studied in the past, but not at extremely low loads. Previous research has been done on high load (50-200 mN) and low load (200-8000 mN) nanoindentation. The applied load in this study ranges from …

Multiphoton Interaction In A System Of Two Quantum Dots, Brian Sawyer

Inquiry: The University of Arkansas Undergraduate Research Journal

As the size and proximity of components on modern computer chips approaches quantum mechanical limits, various novel solutions have been proposed to ensure further increases in processing speed and reliability. Of these, small semiconductor devices called quantum dots may constitute the logic gates of future quantum computers - processors taking advantage of phenomena such as entanglement and quantum teleportation to enable ultra-fast computation speeds. Quantum dots behave much like designer atoms in that their absorption/emission energies can be adjusted lo desired values. A quantum mechanical model of semiconductor quantum dots having equal size and interacting with a single-mode electric field …

Schroedinger Equation With Spherically Averaged Potentials, C. A. Hughes

Journal of the Arkansas Academy of Science

Using a method adapted from few—body hyperspherical techniques, an approach to the solution of the Schroedinger equation with nonspherical potentials is discussed. The method is to spherically average the potential over spherical angles and then solve the resulting set of coupled differential equations. A discussion of how this method is applied to the Stark effect is presented.

Design And Construction Of An Inexpensive Anechoic Chamber, Charles E. Hughes Jr.

Journal of the Arkansas Academy of Science

No abstract provided.