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Weichselbaum, Andreas. "Nanoscale Quantum Dynamics and Electrostatic Coupling." Ohio University / OhioLINK, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1091115085.
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Chenaghlou, Alireza. "Quantum corrections to the classical reflection factor of the sinh-Gordon model." Thesis, Durham University, 2000. http://etheses.dur.ac.uk/4347/.
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This thesis studies the quantum reflection factor of the sinh-Gordon model under boundary conditions consistent with integrability. First, we review the affine Toda field theory in Chapter One. In particular, the classical and quantum integrability of the theory are reviewed on the whole line and on the half-line as well, that is, in the presence of a boundary. We next consider the sinh-Gordon model which is restricted to a half-line by boundary conditions maintaining integrability in Chapter Two. A perturbative calculation of the reflection factor is given to one loop order in the bulk coupling and to first order in the difference of the two parameters introduced at the boundary. The result provides a further verification of Ghoshal's formula. The calculation is consistent with a conjecture for the general dependence of the reflection factor on the boundary parameters and the bulk coupling. In Chapter Three, quantum corrections to the classical reflection factor of the sinh-Gordon model are studied up to second order in the difference of boundary data and to one loop order in the bulk coupling. Chapter Four deals with the quantum reflection factor for the sinh-Gordon model with general boundary conditions. The model is studied under boundary conditions which are compatible with integrability and in the framework of the conventional perturbation theory generalised to the affine Toda field theory. It is found that the general form of a subset of the related quantum corrections are hypergeometric functions. Finally, we sum up this thesis in Chapter Five along with some conclusions and suggestions for further future studies.
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Ablikim, Medina. "Boundary sinh-Gordon model and its supersymmetric extension." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4853/.
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Three different aspects of the sinh-Gordon model are explored in this thesis. We begin, in chapter one, with a summary of the model and the necessary background. Chapter two studies the model with two boundary conditions. Two approaches are presented to investigate the reflection factors off the boundaries and the energy of the theory. In chapter three, perturbation theory is developed to study the theory with one general boundary condition. A contribution to the quantum reflection factor is obtained and compared with the result obtained for the special boundary condition. Chapters four and five investigate the supersymmetric extension of the model in the presence of a single boundary. Firstly, the classical limits of the supersymmetric reflection matrices are checked. The exact reflection factors are studied perturbatively up to the second order of the coupling constant. Secondly, the perturbation theory and the path integral formalism are employed in the supersymmetric model to study the quantum reflection factors. We conclude with a brief sixth chapter describing the outlook for further investigations.
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Niemi, David. "Coupling down converted light into single mode fibers /." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1827.pdf.
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Restrepo, Juan Sebastián. "Theory of quantum optomechanics with unconventional nonlinear coupling schemes." Paris 7, 2014. http://www.theses.fr/2014PA077228.
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Ces dernières années la zoologie de systèmes quantiques apprivoisés a vu l'entrée d'un nouveau membre. Dans le domaine des cavités optomécaniques on a démontré qu'il est possible d'amener des résonateurs micro et nanométriques vers leur état quantique fondamental. Ce fait est rendu possible par la capacité de ces cavités à refroidir optiquement les fluctuations browniennes des degrés de liberté mécaniques. Nous étudions des mécanismes non conventionnels de refroidissement optique dans des cavités optomécaniques. En particulier nous discutons comment les forces photothermiques (ou bolométriques) pourraient permettre d'atteindre l'état quantique fondamental d'un résonateur mécanique, et ce dans des régimes de paramètres où le refroidissement usuel par pression de radiation est limité. D'autre part la maturité expérimentale des cavités optomécaniques •Permet aujourd'hui d'explorer des régimes de couplage fort où un seul photon est suffisant pour perturber le résonateur mécanique au delà de ses fluctuations de point zéro. Suivant cette tendance nous présentons nos prédictions théoriques concernant un système qui combine l'électrodynamique quantique de cavité et l'optomécanique quantique. Nous démontrons que l'introduction d'un atome artificiel à deux niveaux dans la cavité optomécanique mène à des régimes de refroidissement et d'amplification inédits. Par ailleurs nous montrons comment la non-linéarité intrinsèque du système à deux niveaux permet d'atteindre des états non-classiques du résonateur mécaniqueIn recent years the zoology of tamed quantum systems has witnessed the arrival of a new member. In the field of optomechanical cavities it has been proven that it is possible to lead micro and nano mechanical resonators to their vibrational quantum ground state. This feat is made possible by the ability of optomechanical resonators to optically cool down the brownian motion of the mechanical degrees of freedom. We study the cooling mechanisms in optomechanical cavities subject to unconventional coupling schemes. In particular we discuss how pfiotothermal cooling leads the mechanical resonator to its ground state in regimes of parameters for which the more usual radiation pressure based cooling is unable to quench effectively enough the thermal brownian motion. On the other hand the maturity of experimental optomechanics has opened the path for the exploration of strong coupling regimes where a single photon is enough to modify the mechanical properties beyond the zero point fluctuations. Following this trend we present as well our predictions for a system combining quantum electrodynamics and quantum optomechanics. We show that by introducing an artificial two level atom inside the optomechanical cavity the cooling and amplification of mechanical motion are greatly modified. We also show how the intrinsic non-linearity of the artificial atom leads to non-classical states of the mechanical resonator
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Niemi, David A. "Coupling Down Converted Light Into Single Mode Fibers." BYU ScholarsArchive, 2007. https://scholarsarchive.byu.edu/etd/893.
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We investigate the influence of the pump and collection mode parameters on the collection efficiency of Type I down converted photons into single mode fibers. For best single and coincidence counting rates, we find that the mode sizes should be close to the same size and that the mode waists should be located near the down-conversion crystal. Larger collection waists give higher collection efficiencies, but lower singles counts.
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Voigtmann, Thomas. "Mode coupling theory of the glass transition in binary mixtures." [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=967122414.
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White, Thomas Patrick. "Theory of resonance and mode coupling in photonic crystal devices." University of Sydney, 2006. http://hdl.handle.net/2123/924.
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Doctor of Philosophy (PhD)In this thesis we consider several novel photonic crystal structures that derive their properties from optical resonances and mode coupling effects. We present first a theoretical analysis of a new class of photonic crystal device based on the combination of mode coupling and Fabry-Perot resonance effects. These structures exhibit characteristics that make them promising candidates as compact, integrated photonic components. The second aspect we consider is highly-efficient coupling into uniform photonic crystals. The results of this study identify inherent advantages of rod-type photonic crystals over the more common hole-type structures for in-band applications. The third contribution of this thesis is the demonstration of an efficient and powerful theoretical approach to studying photonic crystal devices. Throughout this work, we combine general numerical methods with simple physical models to develop physical insight into the behaviour of photonic crystal structures. We show that this can lead to novel device geometries with highly attractive properties.
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White, Thomas P. "Theory of resonance and mode coupling in photonic crystal devices." Connect to full text, 2005. http://hdl.handle.net/2123/924.
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Thesis (Ph. D.)--University of Sydney, 2006.Title from title screen (viewed 30 May 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Physics, Faculty of Science. "Centre for Ultrahigh-bandwidth Devices for Optical Systems" -- T.p. Degree awarded 2006; thesis submitted 2005. Includes bibliographical references. Also available in print form.
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White, Thomas Patrick. "Theory of resonance and mode coupling in photonic crystal devices." Thesis, The University of Sydney, 2005. http://hdl.handle.net/2123/924.
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In this thesis we consider several novel photonic crystal structures that derive their properties from optical resonances and mode coupling effects. We present first a theoretical analysis of a new class of photonic crystal device based on the combination of mode coupling and Fabry-Perot resonance effects. These structures exhibit characteristics that make them promising candidates as compact, integrated photonic components. The second aspect we consider is highly-efficient coupling into uniform photonic crystals. The results of this study identify inherent advantages of rod-type photonic crystals over the more common hole-type structures for in-band applications. The third contribution of this thesis is the demonstration of an efficient and powerful theoretical approach to studying photonic crystal devices. Throughout this work, we combine general numerical methods with simple physical models to develop physical insight into the behaviour of photonic crystal structures. We show that this can lead to novel device geometries with highly attractive properties.
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Lindmark, Eric Karl 1965. "Erbium-doped GaAs/AlGaAs quantum wells and normal mode coupling of semiconductor microcavities." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/282329.
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This dissertation investigated two different types of semiconductor heterostructures grown by molecular beam epitaxy. The first were erbium-doped GaAs/AlGaAs quantum well structures with concentrations of Er in the range of 10¹⁷-2 x 10¹⁹ cm⁻³. Photoluminescence (PL) of Er³⁺ ions and Er-induced defects were studied at liquid helium and higher temperatures. A strong diffusion of erbium and interdiffusion of gallium and aluminum ions were observed at the boundary of the GaAs/AlGaAs quantum wells which led, at high erbium concentrations, to the degradation of the quantum wells and macroscopic (average) leveling of the erbium and aluminum concentrations over the whole semiconductor structure. From high-resolution PL spectra the existence of three types of Er centers was deduced that differ by the positions of fine structure lines, PL lifetimes, and PL temperature dependence. Our results indicate that these centers are accompanied by the appearance of three types of carrier traps. Our experiments give evidence that the carriers captured into these traps control the Auger excitation of Er ions. Besides erbium luminescence at 1.54 μm, we have observed luminescence of erbium ions from upper excited states at 0.82 and 0.98 μm which demonstrates the possibility of realizing a three-level scheme of light emission. The second structures investigated were GaAs/AlAs microcavities containing different numbers of identical and non-identical quantum wells. The normal mode coupling behavior of these structures was studied, including the differences from the atomic case. For the identical quantum well structures we examined their linear and nonlinear behavior and modeled this behavior using a transfer matrix method. For the non-identical quantum well case we measured three-dip reflectivity spectra characteristic of three coupled oscillators. A theoretical model based on a nonlocal dielectric response and a transfer matrix method was used to model the microcavities and yielded good agreement with experiment. A simpler model using dispersion theory was also described that gave good qualitative agreement to the measurements.
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Schmid, Bernhard [Verfasser]. "Mode-coupling theory: generalizations, high dimensions and microscopic dynamics / Bernhard Schmid." Mainz : Universitätsbibliothek Mainz, 2011. http://d-nb.info/1026802563/34.
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Funk, Andrew Christopher. "Cryptography using two-mode quantum mechanically squeezed optical pulses /." view abstract or download file of text, 2004. http://wwwlib.umi.com/cr/uoregon/fullcit?p3120623.
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Thesis (Ph. D.)--University of Oregon, 2004.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 204-209). Also available for download via the World Wide Web; free to University of Oregon users.
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Ryan, James Patrick. "Coupling matter to quantum gravity in the group field theory approach." Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613184.
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Peall, Robert George. "The effects of strong coupling between waveguides in integrated optics." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257957.
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Clarke, John Nicholas. "Applications of modern valence bond theory to small molecules." Thesis, University of Liverpool, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260246.
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Liluashvili, Alexander [Verfasser], and Hartmut [Gutachter] Löwen. "Mode Coupling Theory of Active Brownian Hard Disks / Alexander Liluashvili ; Gutachter: Hartmut Löwen." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2018. http://d-nb.info/1151383201/34.
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Whiteman, Robert Ralph. "Resolution of the energy level structure of quantum mechanical squid rings." Thesis, University of South Wales, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239527.
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Witzany, Marcus [Verfasser]. "The lasing transition and strong mode coupling in InP quantum dot based GaInP microdisk cavity structures / Marcus Witzany." München : Verlag Dr. Hut, 2012. http://d-nb.info/1028783663/34.
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Mumba, Mambwe. "EFFECTS OF COUPLING BETWEEN CENTER OF MASS MOTION OF AN ATOM AND A CAVITY MODE: PHOTON STATISTICS AND WAVE-PARTICLE CORRELATIONS." Connect to this document online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=miami1121433361.
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Thesis (M.S.)--Miami University, Dept. of Physics, 2005.Title from first page of PDF document. Document formatted into pages; contains [1], v, 296 p. : ill. Includes bibliographical references (p. 393-396).
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Vogt, Markus O. "Toward coherent ion-cavity coupling." Thesis, University of Sussex, 2017. http://sro.sussex.ac.uk/id/eprint/68376/.
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Entanglement is an established resource in quantum information processing, and there is a clear imperative to study many-body systems both in quantum technology applications and for probing fundamental physical laws. Ion trap cavity quantum electrodynamics is a highly promising platform for research. Prerequisites are the controlled coupling of many ions to the cavity field along with the ability to initialize the quantum states and drive coherent transitions between them. A coaxial ion trap and high finesse cavity system has been shown to couple strings of up to five ions to the cavity mode with nearly optimal coupling strength thanks to precise control over their positions in the standing wave and their mutual Coulomb interaction. The predictive power of the theoretical model demonstrates that the scheme can be extended to more ions or to higher coupling regimes. In a separate experiment it has been demonstrated that a quantum state can be initialized, before coherently transferring the population to a qubit state through the cavity interaction. The emission of polarized photons in the cavity mode has been measured, taking the system closer to the generation of cluster states for quantum information research and fundamental studies in many-body entanglement. Building on the aforementioned work, an infrastructure has been put in place for the direct observation of vacuum Rabi oscillations between a single ion and the cavity. In this scheme, the contribution to the dynamics from the dominant incoherent channel is minimized through post-selection of the data. As a quantum system coupled to a reservoir with memory, it will provide experimental constraints on theoretical work in the field of non-Markovian dynamics.
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Yang, Yongwu. "Impulsive stimulated light scattering from glass-forming liquids : structural relaxation, orientational relaxation and testing of mode coupling theory." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10596.
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Sharkey, Kieran James. "An investigation of the running coupling and meson masses in lattice QCD." Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343926.
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Niro, Pierluigi. "Strong coupling in 2+1 dimensions from dualities, holography, and large N." Doctoral thesis, Universite Libre de Bruxelles, 2021. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/327659.
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The goal of the original research presented in this thesis is to study the strong coupling regime of Quantum Field Theories (QFTs) with different methods, making concrete predictions about the phase structure and the dynamics of these theories, and on their observables. The focus is on (gauge) field theories in three spacetime dimensions, which are an interesting laboratory to understand the properties of strong coupling in setups that are usually simpler than in the more familiar case of gauge theories in four dimensions. Importantly, topological effects play a relevant role in three dimensions, thanks to the presence of the so-called Chern-Simons term.The thesis contains a short introduction to QFTs in 3d, principles and applications of infrared dualities, large N techniques, and holography. Indeed, the web of infrared dualities, the large N expansion, and the holographic correspondence between QFT and gravity are the main tools which we use to investigate the strongly coupled regimes of 3d QFTs.Then, the original material is presented. In a first line of research, we focus on the study of the phase diagram of a 3d gauge theory making use of conjectured infrared dualities, extending such dualities to the case where more than one mass parameter can be dialed. In a second line of research, we study a class of 3d gauge theories by engineering their gravity dual in a string theory setup. We prove the existence of multiple phase transitions between phases characterized by both massless particles and topological sectors. In a third line of research, we use holography as a tool to explore the interplay between the physics of 4d QCD and 3d gauge theories. In particular, we analyze the properties of 3d domain walls, which appear as soliton-like solutions of 4d QCD in specific parametric regimes. Finally, we propose a boundary construction of 3d large N vector models, which appear as critical points of theories obtained by coupling degrees of freedom localized on a 3d boundary to a 4d bulk theory. This construction allows to prove new dualities and uncovers a new computational tool for 3d vector models.Doctorat en Sciences
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Alves, Ricardo Joao Gaio. "A convergent reformulation of perturbative QCD." Thesis, Durham University, 2000. http://etheses.dur.ac.uk/4259/.
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We present and explore a new formulation of perturbative QCD based not on the renormalised coupling but on the dimensional transmutation parameter of the theory and the property of asymptotic scaling. The approach yields a continued function, the iterated function being that involved in the solution of the two-loop β-function equation. In the so-called large-b limit the continued function reduces to a continued fraction and the successive approximants are diagonal Padé approximants. We investigate numerically the convergence of successive approximants using the leading-b approximation, motivated by renormalons, to model the all-orders result. We consider the Adler D-function of vacuum polarisation, the Polarised Bjorken and Gross-Llewellyn Smith sum rules, the (unpolarised) Bjorken sum rule, and the Minkowskian quantities R(_r) and the R-ratio of e(^+)e(^-) annihilation. In contrast to diagonal Fade approximants the truncated continued function method gives remarkably stable large-order approximants in cases where infra-red renormalon effects are important. We also use the new approach to determine the QCD fundamental parameters from the R(_r) and the R-ratio measurements, where we find Ā(^(3))(_MS)=516±48 MeV (which yields a(_s)(µ=m(_r))=0.360(^+0.021)(_=0.020)), and Ā(^(5))(_MS)=299(^+6)(_-7) MeV (which yields a(_s)(µ=m(_zo)=0.1218±0.0004), respectively. The evolution of the former value to the m(_zo) energy results in a(_s)(µ= m(_zo)) = 0.123 ± 0.002. These values are in line with other determinations available in the literature. We implement the Complete Renormalisation Group Improvement (CORGI) scheme throughout all the calculations. We report on how the mathematical concept of Stieltjes series can be used to assess the convergence of Padé approximants of perturbative series. We find that the combinations of UV renormalons which occur in perturbative QCD may or may not be Stieltjes series depending on the renormalisation scheme used.
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Fairbairn, Malcolm. "Cosmological and theoretical aspects of higher dimensions." Thesis, University of Sussex, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367330.
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Lévêque, Camille. "Pump-probe spectroscopy of vibronic dynamics using high-order harmonic generation : general theory and applications to SO2." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066513/document.
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La molécule SO2 est connue depuis longtemps dans la pour son spectre d'absorption compliqué résultant de forts couplages entre les états électroniques impliqués. Cette longue histoire a récemment été complétée par de nouvelles études spectroscopiques résolues en temps; la spectroscopie de photoémission (TRPES) et la génération d'harmoniques d'ordre élevé. De nouvelles questions ont ainsi émergées, concernant le rôle des différents états électroniques excités, les différents couplages et leur temps caractéristiques. Pour répondre à ces questions, nous avons considéré, dans un premier temps, l'état électronique fondamental et les deux premiers états singulets excités. Ceux-ci interagissent par l'intermédiaire de couplage non-adiabatic, conduisant à la complexité du spectre d'absorption. Nos résultats se sont avérés particulièrement précis, en particulier pour la description des bandes de Cléments, donnant lieu à leur première description et interprétation théorique. Le couplage spin-orbite et les états triplets ont été introduits dans la description du système et l'analyse de la dynamique a permis de comprendre les différents mécanismes de conversion intersystème. Trois résultats majeurs sont obtenus, (i) le rôle prédominant d'un état 3B2, (ii) la présence d'interférences quantiques lors du processus et (iii) une nouvelle interprétation de la bande dite " interdite ", émanant des état triplets. Les spectroscopies TRPES et HHG ont été utilisées pour sonder la dynamique moléculaire dans ces états. Grâce à des simulations ab-initio nous montrons que la méthode TRPES permet l'étude la dynamique pour tous les états alors que la HHG n'est sensible qu'à la conversion intersystèmeThe SO2 molecule is long known in the literature for its complex UV absorption spectrum, which is caused by a variety of strong couplings between the electronic states involved. This long and rich history was augmented recently by new time-dependent spectroscopic methods, namely, Time-Resolved Photoelectron Spectroscopy (TRPES) and High-order Harmonic Generation (HHG). Additional open questions emerged immediately, e.g., what was the role of the different known electronic states, which were the relevant couplings and also the timescales of the different relevant processes.To resolve these issues theoretically, we start by considering the electronic ground state and the two lowest singlet excited states. The latter interact through non-adiabatic couplings leading to a complex photoabsorption spectrum. Our results were accurate, especially concerning the Clements bands, and provide a comprehensive description of the photoabsorption spectrum. When including the spin-orbit coupling, relevant for the weak long-wavelength absorption system, the three-states model turns into a 12 coupled-states system. Analysis of the different couplings gives insight into the different mechanisms of the intersystem crossing. Three main points are shown: (i) the preponderant role of a 3B2 state, (ii) the possibility of quantum interferences during the process and (iii) a new interpretation of the forbidden band.The TRPES and the HHG spectroscopies have been used to probe the time-dependent dynamics in all these states. With the aid of first-principles simulations we show that the TRPES method is sensitive to the dynamics in the manifold, while HHG is sensitive only to the intersystem crossing
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Konincks, Thomas. "Structure and dynamics of fluids in quenched-random potential energy landscapes." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEN076/document.
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De récentes études expérimentales de la dynamique de colloïdes illuminés par une figure d'interférence optique aléatoire (tavelures ou speckle) ont montré l'existence de phénomènes de sous-diffusion, de piégeage, ou de ségrégation dans le cas de mélanges, sous l'effet de cet environnement désordonné. L'objet de ce travail de doctorat est d'approfondir la compréhension de ces phénomènes par une étude théorique. Dans ce but, une version de la théorie de couplage de modes (MCT), initialement développée pour les fluides confinés dans des solides poreux désordonnés, a été appliquée au cas d'un fluide plongé dans un potentiel aléatoire gaussien de covariance gaussienne. La résolution numérique des équations asymptotiques de cette théorie a permis la construction de diagrammes d'état, lesquels reproduisent, par exemple, le comportement réentrant non trivial de la diffusivité observé dans les expériences, dont une interprétation physique simple est proposée.Les résultats suggèrent en outre une forte dépendance de la dynamique du système par rapport à la longueur de corrélation du désordre. Une étude détaillée de la relaxation du fluide a été effectuée, dans le but d'apporter une compréhension de la dynamique à toutes les échelles de temps. En parallèle, il a été montré que de nombreuses approximations classiques utilisées dans le calcul des propriétés structurales des fluides conduisent à des résultats non physiques dans le cas présent.Finalement, un programme de simulation Monte Carlo a été développé, et les premiers résultats sont comparés à la théorie et aux expériencesRecent experimental studies of the dynamics of colloids beamed by a random light pattern (speckle) showed the existence of subdiffusion, trapping, or mixture separation phenomena, under the action of that disordered environment.To this end, a version of the Mode Coupling Theory (MCT), initially developed for fluids in confinement in sol id porous matrices has been applied to the case of a fluid plunged in a random Gaussian potential with a Gaussian correlation function.The aim of this PhD work is to further improve the understanding of these phenomena by the addition of a theoretical study.The numerical resolution of the asymptotic equations of this theory leads to the construction o phase diagrams, which reproduce for example the non trivial reentrent behaviour of the diffusivity, observed in related experiments, for which a physical interpretation is proposed. Furthermore, results suggest a strong depend ence of the dynamics on the disorder correlation length. A detailed study of the relaxation of the fluid has been made, in order to bring an understandin( of the dynamics at ali timescales. Simultaneously, it has been showed that a number of common approximations used in the calculation of the structural properties of fluids lead in the present case to non-physical results. Finally, a Monte-Carlo simulation program has been developed, and the first results are compared to theory and experiments
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Lundqvist, Maria J. "Quantum Chemical Modeling of Dye-Sensitized Titanium Dioxide : Ruthenium Polypyridyl and Perylene Dyes, TiO2 Nanoparticles, and Their Interfaces." Doctoral thesis, Uppsala universitet, Kvantkemi, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7141.
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Quantum chemical calculations have been used to model dye-sensitized nanostructured titanium dioxide systems that can be used in solar cells for solar energy to electricity conversion. Structural, electronic and spectral properties of isolated dyes and both bare and dye-sensitized TiO2 have been calculated with density functional theory, providing detailed information about both the separate parts and the dye-TiO2 interface. The connection between the geometry, the ligand field splitting and the lifetime of the triplet metal-to-ligand charge transfer (MLCT) excited state has been explored for a series of ruthenium polypyridyl dyes. Moreover, the relative energetics of MLCT and metal centered triplet excited states have been studied for a number of such systems. It was found that small alterations of the polypyridyl ligands can result in significant changes in ligand field splitting and in the energetics of the triplet states. Attachment of the dyes to the TiO2 surface is achieved via anchor and spacer groups. The influence of such groups on various properties of the dye and their ability to act as mediators of photo-induced surface electron transfer has been studied. Delocalization of the lowest unoccupied dye orbital onto the spacer and/or anchor group indicates that certain unsaturated groups can mediate electron transfer. With a combination of methods that enables efficient computations and a scheme for construction of metal oxide clusters, chemical models for bare TiO2 nanocrystals in the 1-2 nm size range have been developed. The electronic structures show well-developed band structures with essentially no electronic band gap defect states. Atomistic models of the interface between TiO2 nanocrystals and Ru(II)-bis-terpyridine dyes, the so-called N3 dye as well as perylene dyes are reported. Electronic coupling strengths, which provide estimates for the electron injection times, are extracted from the interfacial electronic structure and the lowest electronic excitations are calculated.
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Da, silva Antonio. "Theoretical determination of optical properties for sapphire doped with titanium from its microscopy and analysis of its capabilities for laser without population inversion." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX075/document.
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Cet exposé est scindé en deux grandes parties. Dans la première, nous estimons des constantes photo-physiques du saphir dopé au titane à partir d'un modèle analytique simple exploitant une théorie de Huang-Rhys pour la détermination du profil spectral des bandes simples et une hypothèse réaliste de superposition de ces dernières. Nous déterminons une formule pour l'indice de réfraction total du Ti:saphir en fonction de la concentration de dopant. Dans une seconde partie, nous évaluons, selon la vérification d'un concept, la capacité de laser sana inversion de populations pour un cristal dopé possédant une basse symétrie. Nous appuyons notre démonstration en établissant une condition de seuil généralisée d'effet laser. Ce concept pourrait être une rupture technologique dans le domaine des grands cristaux dopés et n'a pas encore été investigué par la communautéThis presentation is split into two main parts. In the first, we estimate photo-physical constants of titanium doped sapphire from a simple analytical model using a Huang-Rhys theory for the determination of the spectral profile of simple bands and from a realistic hypothesis of superposition of the latter. We define a formula for the total refractive index of Ti:sapphire as a function of dopant concentration. In a second part, we evaluate, according to the verification of a concept, the laser capability without population inversion for a doped crystal with low symmetry. We support our demonstration by establishing a generalized laser threshold condition. This concept would be a technological breakthrough in the field of large doped crystals and has not yet been investigated by the community
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Flick, Johannes [Verfasser], Claudia [Gutachter] Draxl, Angel [Gutachter] Rubio, and Dieter [Gutachter] Bauer. "Exact nonadiabatic many-body dynamics : electron-phonon coupling in photoelectron spectroscopy and light-matter interactions in quantum electrodynamical density-functional theory / Johannes Flick. Gutachter: Claudia Draxl ; Angel Rubio ; Dieter Bauer." Berlin : Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://d-nb.info/1112595929/34.
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Griffiths, Scott. "Reggeons in pQCD." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297421.
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Mondal, Ritwik. "Relativistic theory of laser-induced magnetization dynamics." Doctoral thesis, Uppsala universitet, Materialteori, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-315247.
Full textAbstract:
Ultrafast dynamical processes in magnetic systems have become the subject of intense research during the last two decades, initiated by the pioneering discovery of femtosecond laser-induced demagnetization in nickel. In this thesis, we develop theory for fast and ultrafast magnetization dynamics. In particular, we build relativistic theory to explain the magnetization dynamics observed at short timescales in pump-probe magneto-optical experiments and compute from first-principles the coherent laser-induced magnetization. In the developed relativistic theory, we start from the fundamental Dirac-Kohn-Sham equation that includes all relativistic effects related to spin and orbital magnetism as well as the magnetic exchange interaction and any external electromagnetic field. As it describes both particle and antiparticle, a separation between them is sought because we focus on low-energy excitations within the particle system. Doing so, we derive the extended Pauli Hamiltonian that captures all relativistic contributions in first order; the most significant one is the full spin-orbit interaction (gauge invariant and Hermitian). Noteworthy, we find that this relativistic framework explains a wide range of dynamical magnetic phenomena. To mention, (i) we show that the phenomenological Landau-Lifshitz-Gilbert equation of spin dynamics can be rigorously obtained from the Dirac-Kohn-Sham equation and we derive an exact expression for the tensorial Gilbert damping. (ii) We derive, from the gauge-invariant part of the spin-orbit interaction, the existence of a relativistic interaction that linearly couples the angular momentum of the electromagnetic field and the electron spin. We show this spin-photon interaction to provide the previously unknown origin of the angular magneto-electric coupling, to explain coherent ultrafast magnetism, and to lead to a new torque, the optical spin-orbit torque. (iii) We derive a definite description of magnetic inertia (spin nutation) in ultrafast magnetization dynamics and show that it is a higher-order spin-orbit effect. (iv) We develop a unified theory of magnetization dynamics that includes spin currents and show that the nonrelativistic spin currents naturally lead to the current-induced spin-transfer torques, whereas the relativistic spin currents lead to spin-orbit torques. (v) Using the relativistic framework together with ab initio magneto-optical calculations we show that relativistic laser-induced spin-flip transitions do not explain the measured large laser-induced demagnetization. Employing the ab initio relativistic framework, we calculate the amount of magnetization that can be imparted in a material by means of circularly polarized light – the so-called inverse Faraday effect. We show the existence of both spin and orbital induced magnetizations, which surprisingly reveal a different behavior. We establish that the laser-induced magnetization is antisymmetric in the light’s helicity for nonmagnets, antiferromagnets and paramagnets; however, it is only asymmetric for ferromagnets.
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Norberg, Daniel. "Quantum Chemical Studies of Radical Cation Rearrangement, Radical Carbonylation, and Homolytic Substitution Reactions." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8178.
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Cullen, M. A. "Perturbative predictions for 4 jet production at LEP and prompt photon emission at the tevatron." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4504/.
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Many contemporary experimental QCD results achieve greater accuracy in measurement than equivalent theoretical predictions calculated at leading order. Therefore it is necessary to consider next to leading order (NLO) predictions for many processes in order to compare experiment with theory. Accurate theoretical predictions are also important in order to reduce the uncertainty in QCD parameters such as the coupling constant a, and to test whether QCD is in fact the correct theory to describe the strong interaction. With NLO results it is also possible to separate different clustering algorithms and test non-perturbative effects. This thesis concentrates on the techniques necessary for the calculation of NLO observables from the processes e(^+)e(^-) → 4 jets and pp → γ + X. We formulate a new version of the hybrid subtraction scheme based on the colour antenna structure of the final state to evaluate the necessary phase space integrals for the 4 jet process. The scheme is universal and can be applied to any QCD processes. The general purpose Monte Carlo EERAD2 which incorporates this new technique is compared with both experimental data gathered by the DELPHI collaboration and other groups which have reported similar calculations. A Monte Carlo written for the process pp → γ + X requires a knowledge of the non- perturbative photon fragmentation function, D(_γ), and the second half of this thesis concentrates on a calculation of this process using the ALEPH measurement of D(_γ) based on a democratic algorithm. The Monte Carlo DPRAD incorporates these techniques and results from it are compared with data from the Tevatron.
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Geier, Kevin Thomas. "Probing Dynamics and Correlations in Cold-Atom Quantum Simulators." Doctoral thesis, Università degli studi di Trento, 2022. http://hdl.handle.net/11572/351120.
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Cold-atom quantum simulators offer unique possibilities to prepare, manipulate, and probe quantum many-body systems. However, despite the high level of control in modern experiments, not all observables of interest are easily accessible. This thesis aims at establishing protocols to measure currently elusive static and dynamic properties of quantum systems. The experimental feasibility of these schemes is illustrated by means of numerical simulations for relevant applications in many-body physics and quantum simulation. In particular, we introduce a general method for measuring dynamical correlations based on non-Hermitian linear response. This enables unbiased tests of the famous fluctuation-dissipation relation as a probe of thermalization in isolated quantum systems. Furthermore, we develop ancilla-based techniques for the measurement of currents and current correlations, permitting the characterization of strongly correlated quantum matter. Another application is geared towards revealing signatures of supersolidity in spin-orbit-coupled Bose gases by exciting the relevant Goldstone modes. Finally, we explore a scenario for quantum-simulating post-inflationary reheating dynamics by parametrically driving a Bose gas into the regime of universal far-from-equilibrium dynamics. The presented protocols also apply to other analog quantum simulation platforms and thus open up promising applications in the field of quantum science and technology.I simulatori quantistici ad atomi freddi offrono possibilità uniche per preparare, manipolare e sondare sistemi quantistici a molti corpi. Tuttavia, nonostante l'alto livello di controllo raggiunto negli esperimenti moderni, non tutte le osservabili di interesse sono facilmente accessibili. Lo scopo di questa tesi è quello di stabilire protocolli per misurare delle proprietà statiche e dinamiche dei sistemi quantistici attualmente inaccessibili. La fattibilità sperimentale di questi schemi è illustrata mediante simulazioni numeriche per applicazioni rilevanti nella fisica a molti corpi e nella simulazione quantistica. In particolare, introduciamo un metodo generale per misurare le correlazioni dinamiche basato su una risposta lineare non hermitiana. Ciò consente test imparziali della famosa relazione fluttuazione-dissipazione come sonda di termalizzazione in sistemi quantistici isolati. Inoltre, sviluppiamo tecniche basate su ancilla per la misura di correnti e correlazioni di corrente, consentendo la caratterizzazione della materia quantistica fortemente correlata. Un'altra applicazione è orientata a rivelare l'impronta della supersolidità nei gas Bose con accoppiamento spin-orbita eccitando il corrispondente modo di Goldstone. Infine, esploriamo uno scenario per la simulazione quantistica della dinamica di riscaldamento post-inflazione modulando parametricamente un gas Bose e portandolo nel regime della dinamica universale lontana dall'equilibrio. I protocolli presentati si applicano anche ad altre piattaforme di simulazione quantistica analogica e aprono quindi applicazioni promettenti nel campo della scienza e della tecnologia quantistica.
Quantensimulatoren auf Basis ultrakalter Atome eröffnen einzigartige Möglichkeiten zur Präparation, Manipulation und Untersuchung von Quanten-Vielteilchen-Systemen. Trotz des hohen Maßes an Kontrolle in modernen Experimenten sind jedoch nicht alle interessanten Observablen auf einfache Weise zugänglich. Ziel dieser Arbeit ist es, Protokolle zur Messung aktuell nur schwer erfassbarer statischer und dynamischer Eigenschaften von Quantensystemen zu etablieren. Die experimentelle Realisierbarkeit dieser Verfahren wird durch numerische Simulationen anhand relevanter Anwendungen in der Vielteilchenphysik und Quantensimulation veranschaulicht. Insbesondere wird eine allgemeine Methode zur Messung dynamischer Korrelationen basierend auf der linearen Antwort auf nicht-hermitesche Störungen vorgestellt. Diese ermöglicht unabhängige Tests des berühmten Fluktuations-Dissipations-Theorems als Indikator der Thermalisierung isolierter Quantensysteme. Darüber hinaus werden Verfahren zur Messung von Strömen und Strom-Korrelationen mittels Kopplung an einen Hilfszustand entwickelt, welche die Charakterisierung stark korrelierter Quantenmaterie erlauben. Eine weitere Anwendung zielt auf die Enthüllung spezifischer Merkmale von Supersolidität in Spin-Bahn-gekoppelten Bose-Einstein-Kondensaten ab, indem die relevanten Goldstone-Moden angeregt werden. Schließlich wird ein Szenario zur Quantensimulation post-inflationärer Thermalisierungsdynamik durch die parametrische Anregung eines Bose-Gases in das Regime universeller Dynamik fern des Gleichgewichts erschlossen. Die dargestellten Protokolle lassen sich auch auf andere Plattformen für analoge Quantensimulation übertragen und eröffnen damit vielversprechende Anwendungen auf dem Gebiet der Quantentechnologie.
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Cheng, Xinru. "Generation of Photon Pairs in Fiber Microcouplers." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/35647.
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Due to its inherent stability and compactness, integrated optics can allow for experimental complexity not currently achievable with bulk optics. This opens up the possibility for large-scale quantum technological applications, such as quantum communication networks and quantum information processing. Quantum information processing relies on efficient sources of entangled photon pairs. Most demonstrations in integrated photonics so far have featured the on-chip manipulation of photon states using a free-space bulk-optic source of photons. This has the drawback of introducing loss due to the spatial mode mismatch between waveguide modes of the chip and modes of the produced photons. In this way, loss limits the number of photons that are simultaneously carried in the integrated optical device, and thus limits the number of qubits. One way to avoid this loss is to generate the photons in another waveguide device. This can be done through, for example, spontaneous four-wave mixing (SFWM). In this third-order nonlinear process, two pump photons spontaneously scatter off each other to create two photons of two new frequencies, satisfying momentum and energy conservation. This has been studied in birefringent optical fibers and photonic crystal fibers.
In this work, we investigate the SFWM generation of photons in a waveguide coupler comprised of two touching tapered optical fibers, which we call a microcoupler. The two silica fibers are kept in contact and tapered to be 1 micron in diameter in the 10 cm long uniform interaction region. This device has three main advantages over a standard telecom 2x2 fiber coupler. 1) The small mode area enhances the photon generation rate; 2) The microcoupler supports four modes which is the minimum number required for two-photon entanglement. So in principle the device should be able to produce polarization-entangled photon pairs; 3) The strong waveguide-waveguide coupling and waveguide dispersion (due to the tapering) forces the photons to be far in wavelength from the background light around the pump. We present the 28 allowed phasematching processes for the microcoupler, as well as predict the frequencies of the generated photons. We report the first experimental observation of photon pairs produced via SFWM in a microcoupler. We also analyze the polarization state of the observed photons to figure out which phasematching processes are responsible for generating the photons.
We expect to observe more photon pairs in future devices, with the ultimate goal being the generation of polarization-entangled photon pairs for integrated optics.
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Tchangnwa, Nya Fridolin. "Transition fluide-verre et verres multiples dans les suspensions colloïdales par la théorie du couplage de mode : rôle de la structure statique." Thesis, Paris Est, 2012. http://www.theses.fr/2012PEST1161.
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La théorie de couplage de mode (MCT) est l'une des méthodes les plus utilisées pour étudier les transitions vitreuses dans les fluides classiques. Ses prédictions sont en général en accord semi quantitatif avec les simulations. Sa mise en oeuvre nécessite la détermination de la structure statique, généralement par résolution des équations d'Orsntein-Zernike avec une fermeture adéquate. Partant de fermetures utilisant des fonctions « bridges » déduites de la fonctionnelle de référence du mélange de sphères dures, notre travail a consisté d'abord à étudier l'influence de la qualité de cette structure statique sur les prédictions relatives aux états non ergodiques dans des mélanges binaires dissymétriques. Nous avons ensuite considéré les résultats de la théorie du couplage de modes dans sa version naïf (NMCT ) et complète, afin d'analyser les mécanismes d'arrêt, les comparer au fluide effectif et aux approches stochastiques (équations de Langevin généralisées). Enfin, nous proposons une version pragmatique de cette méthode qui fournit des prédictions en meilleur accord quantitatif avec les résultats des simulations pour une variété de potentiels d'interactionThe mode coupling theory (MCT) is one of the most widely used methods for studying the glass transition in classical fluids. Its predictions are usually in semi-quantitative agreement with simulation. Its implementation requires the determination of the static structure usually from the Ornstein-Zernike equations with a suitable closure. Starting from closures that use bridge functions deduced from the hard-sphere reference functional, our work consisted first in studying the influence of the quality of this static structure on the predictions concerning the non-ergodic states in asymmetric binary mixtures. We next considered the results of the mode coupling theory in its naive and full versions, in order to analyze the arrest mechanisms and compare them to the effective fluid and the stochastic approaches (generalized Langevin equations). Finally, we propose a pragmatic version of this method that provides predictions in better quantitative agreement with simulations for a variety of interaction potentials
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Frey, Stephan. "Propriétés viscoélastqiues des fondus de polymères vitrifiables." Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAE008/document.
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À l'approche de la transition vitreuse les fondus de polymères montrent une augmentation importante de la viscosité de plusieurs ordres de grandeur. Le but de cette étude est d'acquérir une compréhension plus profonde des propriétés viscoélastiques des fondus de polymères vitrifiables. Les polymères sont modélisés comme des chaînes flexibles en utilisant un modèle de bille-ressort. Les propriétés dynamiques sont analysées dans le cadre de la théorie de couplage de mode idéale. Nous constatons que la température critique de couplage de mode varie avec l'inverse de la longueur de chaîne. En étudiant la fonction de relaxation de cisaillement, nous constatons que les processus de relaxation polymériques, ne sont pas modifiés, mais décalés vers des temps plus importants en approchant la transition vitreusePolymer melts show a remarkable increase of their viscosity by many orders of magnitude on approaching the glass transition. The aim of this study is to gain a deeper insight into the viscoelastic properties of glass forming polymer melts. The polymers are modeled as flexible chains using a bead-spring model. The dynamic properties are analyzed in the framework of the ideal mode-coupling theory. We find that the critical temperature of the ideal mode-coupling theory scales with the reciprocal chain length. By studying the shear relaxation function we find that the polymer relaxation processes are not altered but shifted to later times in the approach of the glass transition
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Prade, Bernard. "Quelques aspects theoriques et experimentaux de la propagation des ondes electromagnetiques dans l'atmosphere et dans une fibre optique monomode." Paris 6, 1987. http://www.theses.fr/1987PA066061.
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Cette these, menee dans le cadre d'un travail sur la transmission d'informations par voie optique, comporte deux parties; la premiere traite du bruit de polarisation introduit par l'atmosphere au repos ou en ecoulement; la seconde partie traite du couplage par champ evanescent dans les fibres monomodes
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Lima, Juliano Alves de. "Projeto, modelagem e fabricação de guias de onda ópticos integrados baseados em polímeros para aplicações em sensores." Universidade de São Paulo, 2002. http://www.teses.usp.br/teses/disponiveis/18/18133/tde-29052017-135956/.
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Este trabalho visa o projeto, modelagem e fabricação de estruturas multicamadas baseadas em polímeros para aplicações como sensores ópticos integrados. A grande motivação para este trabalho está no fato de que estas estruturas, diferente da geometria Mach-Zehnder, dispensam o uso de litografia pois são completamente planares. Isto permite uma diminuição no custo de fabricação dos dispositivos além de permitir que estruturas mais curtas sejam utilizadas. Em se tratando de óptica integrada, as dimensões reduzidas da estrutura impõem severas penalidades no processo de lançamento de potência óptica na mesma. Por isso, será considerada neste estudo a utilização de prismas para o acoplamento de entrada do acoplador. Esta técnica, além de reduzir drasticamente os problemas de alinhamento decorrentes de acoplamento convencional do tipo \"End Fire\", permite uma transferência de potência óptica superior a 80% entre a fibra e o guia retangular. As variações na transferência de potência entre os guias de ondas da estrutura multicamada serão medidas através de um fotodetetor MSM integrado ao sensor. Este detetor, além de sua extrema facilidade de fabricação e baixos custos, torna o conjunto sensor mais robusto. Em se tratando de uma proposta de plataforma para sensores, serão também investigadas possíveis aplicações para esta estrutura, como por exemplo: refratômetro integrado, sensor de glicose, sensor de adulteração de combustível, etc. A análise das estruturas será efetuada por meio de técnicas de modelagem analíticas (Técnica da Matriz de Transferência - TMT e Teoria de Modos Acoplados - TMA), e numéricas (Método da Propagação de Feixe de Ângulo Largo formulado em Diferenças Finitas - WA-FD-BPM). Esta última permite que a estrutura do fotodetetor seja levada em consideração simultaneamente nas simulações.This work concerns with design, modeling and fabrication of polymer based planar multilayer structures for integrated optic sensor applications. The motivation for this work is that planar multilayer structures, differently from the Mach-Zehnder geometry, do not require a lithographic process. As a consequence, significantly cheaper and shorter structures can be realized. The reduced dimensions of the structure, by its turn, pose a severe penalty in terms of optical power coupling. Therefore, this investigation will focus primarily on input (and output) prism coupling configuration. This technique, besides reducing the alignment requirements observed for conventional end-fire coupling, allows optical power coupling efficiency as high as 80% from fiber to rectangular waveguide. Any optical power transfer between the waveguides of the multilayer structure will be detected by an MSM photodetector integrated with the sensor. This low cost photodetector, besides improving the structure robustness, is quite ease to fabricate. Since the idea of this work is to develop a platform for integrated optic sensors, it will also be investigated possible applications for this structure, such as: integrated optic refractometer, glucose sensor and fuel adulteration sensor. The analysis of such structures will be carried out by means of analythical (Transfer Matrix Technique-TMT and Coupled Mode Theory-CMT) and numerical (Wide-Angle Finite Difference Beam Propagation Method-WA-FD-BPM) modeling techniques. The WA-FD-BPM technique allows one to simulate the multilayer waveguide and the MSM photodetector simultaneously.
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Ruscher, Céline. "The Voronoi liquid : a new model to probe the glass transition." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAE027/document.
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Comprendre l’origine microscopique du ralentissement de la dynamique au voisinage de la transition vitreuse reste l’un des problèmes fondamentaux de la physique de la matière condensée. Au cours de ce travail, nous introduisons un nouveau modèle de liquide, appelé liquide de Voronoï, et dont les interactions sont directement reliées aux propriétés géométriques des tessellations de Voronoï. Pour cette classe de liquides, les interactions sont à plusieurs corps et agissent de telle sorte que le système est toujours sous tension tout en restant stable. Le but de ce travail est d’étudier un mélange binaire du liquide de Voronoï et de voir de quelles façons ces interactions exotiques affectent le scénario habituel de la transition vitreuse. Tout au long de ce travail, nous caractérisons le liquide de Voronoï bidisperse théoriquement et par le biais des simulations numériques. Nous proposons également des comparaisons avec des liquides de Lennard-Jones surfondus bien décrit dans la littératureUnderstanding the origin of the important slowing down of the dynamics near glass transition is still one of the remaining fundamental problems of condensed matter physics. During this work we introduced a brand-new model of liquids named Voronoi liquid, whose interactions are directly related to the geometrical properties of Voronoi tessellations. For these class of liquids interactions are intrinsically manybody and act in such a way that the liquid is always under tension but remains stable. The aim of this work is to use a binary mixture of the Voronoi liquid to see to what extend these exotic interactions may affect the classical scenario of glass transition. Throughout this work we characterize theoretically and by mean of numerical simulation the bidisperse Voronoi liquid. Comparisons with well-known Lennard-Jones glass formers are systematically performed
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Ayed, Othman. "Etude des interactions entre atomes alcalins (li, na, k) et monoxyde de carbone en matrices de gaz rares : analyse en spectroscopie vibrationnelle et calcul quantiques de quelques complexes." Paris 6, 1987. http://www.theses.fr/1987PA066117.
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Dans le cas de li(le plus reactif), identification de li(co)::(n), ou n = 1,2,3,4,(ou 6), avec des frequences de vibration de valence de co plus perturbees que pour les metaux de transition carbonyle,et de li::(m) co, ou m = 2,3, avec frequences nu (co) abaissees. Pour na et k, observation d'especes de haute stoechiometrie (c::(n)o::(n))**(2-) (m**(+))::(2) ou n = 2,3,4, formees apres irradiation uv-visible et correspondant a des transformations chimiques. Essai d'interpretation de ces differences de reactivite par une description quantique des agregats de plus basse stoechiometrie : dans le complexe 1 :1, les deux etats electroniques inferieurs sont l'etat **(2)sigma non liant et l'etat **(2)pi liant; la courbe de potentiel de lico possede un minimum pour li-c equiv. A 2,5 a au-dessous de la courbe de l'etat **(2)pi alors que pour naco, le minimum de la courbe pour l'etat **(2)pi est au-dessous de la courbe de l'etat **(2)sigma ; le calcul met en evidence le caractere ionique de m::(2)c::(2)o::(2) (acetylenediolate) resultant d'une reaction chimique
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Dednam, Wynand. "Atomistic simulations of competing influences on electron transport across metal nanocontacts." Thesis, Universidad de Alicante, 2019. http://hdl.handle.net/10500/26155.
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In our pursuit of ever smaller transistors, with greater computational throughput, many
questions arise about how material properties change with size, and how these properties
may be modelled more accurately. Metallic nanocontacts, especially those for which
magnetic properties are important, are of great interest due to their potential spintronic
applications. Yet, serious challenges remain from the standpoint of theoretical and
computational modelling, particularly with respect to the coupling of the spin and lattice
degrees of freedom in ferromagnetic nanocontacts in emerging spintronic technologies. In
this thesis, an extended method is developed, and applied for the first time, to model the
interplay between magnetism and atomic structure in transition metal nanocontacts. The
dynamic evolution of the model contacts emulates the experimental approaches used in
scanning tunnelling microscopy and mechanically controllable break junctions, and is
realised in this work by classical molecular dynamics and, for the first time, spin-lattice
dynamics. The electronic structure of the model contacts is calculated via plane-wave and
local-atomic orbital density functional theory, at the scalar- and vector-relativistic level of
sophistication. The effects of scalar-relativistic and/or spin-orbit coupling on a number of
emergent properties exhibited by transition metal nanocontacts, in experimental
measurements of conductance, are elucidated by non-equilibrium Green’s Function
quantum transport calculations. The impact of relativistic effects during contact formation
in non-magnetic gold is quantified, and it is found that scalar-relativistic effects enhance the force of attraction between gold atoms much more than between between atoms which
do not have significant relativistic effects, such as silver atoms. The role of non-collinear
magnetism in the electronic transport of iron and nickel nanocontacts is clarified, and it is
found that the most-likely conductance values reported for these metals, at first- and lastcontact,
are determined by geometrical factors, such as the degree of covalent bonding in
iron, and the preference of a certain crystallographic orientation in nickel.Physics
Ph. D. (Physics)
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Das, Ankita. "Dynamics of Quantum Supercooled Liquids: A Mode Coupling Approach." Thesis, 2022. https://etd.iisc.ac.in/handle/2005/5873.
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In this thesis, I use the quantum mode coupling theory (QMCT) formulation to
study the dynamics in a supercooled liquid to understand how quantum fluctuations affect the liquid-glass transition. I calculate the Kubo-transformed density
correlation function in order to avoid the difficulties associated with the direct
calculation of the quantum correlation functions. The Kubo and the quantum
correlation functions are connected through a mapping of quantum particles
into classical ring-polymers. The radius of gyration of the polymer is directly
related to the uncertainty in the position of the quantum particle. The position
uncertainty increases with the quantumness of the system, which is quantified
in terms of the thermal de-Broglie wavelength.
I propose a perturbative method to simplify the form of the self-consistent
equations of QMCT, which makes it feasible to study the relaxation dynamics
directly in the time-domain, significantly reducing the computational cost. Implementing the perturbative calculation in the hard-sphere supercooled liquid,
I find that moderate quantum fluctuations can cause enhanced caging, leading
to liquid-glass transition at densities smaller than the classical transition density.
The relaxation time associated with the density fluctuations shows power-law
divergence with increasing density, similar to the classical HS system. However,
the power-law exponents show a linear rise with increasing quantum fluctuations, which suggests a dynamic nature of the quantum effect. Further, at a
fixed density, far from transition point, relaxation time shows an exponential
(Vogel-Fulcher-Tamman) increase with the quantum fluctuation, which crosses
over to a power-law like divergence as the transition point is approached.
Extending the study to higher quantum regime, I observe that an enhanced
tunneling effect leads to a re-entrant transition from glass to liquid phase. The
intervening glass phase allows us to divide the liquid phase into two: low and
xii
high quantum liquids. The relaxation time in the high quantum regime shows a
power-law like divergence as the liquid-glass transition point is approached. The
study shows faster relaxation in the higher quantum regime due to enhanced
tunneling.
I further analyze the frequency-dependent specific heat in the supercooled
quantum liquid. Liquid-glass transition is generally thought of as a second order
phase transition; thus specific heat measurement is one of the important tools
to detect it. I use QMCT and Zwanzig’s formalism to express specific heat in
terms of the longitudinal viscosity of the liquid. I find a substantial variation
in frequency-dependence of the specific heat as the quantumness of the liquid
is changed, and this variation becomes more significant as the density of the
system is increased. Near the glass transition point, slower dynamical modes
contribute to the specific heat in quantum liquids as compared to the classical
liquids.
Another fundamental observable to analyze relaxation processes in liquids
is the tagged-particle dynamics. The tagged-particle density correlation acts
as the generating function of the moments of tagged-particle displacement. I
derive a coupled set of equations for the second and the fourth moments (Kubotransformed) of tagged-particle displacement using QMCT. The most interesting
results for these moments are obtained in the short times which are related to
the uncertainty due to quantum fluctuation. The non-zero values of the moments at zero-time due to quantum uncertainty stands out from the classical
case. The non-Gaussian nature of the particle distribution function at short (ballistic) times leading to strong dynamical heterogeneity in the tagged-particle
motion further reflects the enhanced quantum effect. I derive an analytic expression for diffusion coefficient which shows non-monotonous behavior with
increasing quantumness and qualitatively reflects the re-entrant diffusive behavior observed in Lennard-Jones simulations.UGC, IISC
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Runov, Boris. "Integrability of Bukhvostov-Lipatov model and ODE/IQFT correspondence." Phd thesis, 2018. http://hdl.handle.net/1885/148417.
Full textAbstract:
We consider Bukhvostov-Lipatov model, an integrable quantum field
theory in two dimensions that arises as an approximation to O(3)
NLSM.
We compute its vacuum energy on a cylinder with twisted boundary
conditions in weak coupling limit using renormalized perturbation
theory, and in the short distance limit using conformal
perturbation theory.
The exact solution of this model via coordinate Bethe ansatz is
provided. Two different regularizations of Bethe ansatz equations
are constructed.
The vacuum state is constructed and the vacuum energy is
computed within both regularizations using numerical methods.
Bethe ansatz equations governing the vacuum state are shown to
coincide with functional relations between connection
coefficients of auxiliary linear problem for an integrable
classical PDE known as modified sinh-Gordon equation. Based on
this correspondence
the system of nonlinear integral equations equivalent to the full
system of Bethe ansatz equations is derived for massive and
conformal cases. This system of NLIE was solved numerically.
We have also used it to investigate analytically the properties
of solution describing vacuum state. Finally, we have derived a
formula that expresses the vacuum energy of Bukhvostov-Lipatov
model in terms of the regularized area of constant mean curvature
surface embedded into ADS3 space.
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Wang, Yuan-Chu. "Photovoltaic and Photoconductive Dual-mode Infrared Photodetector Made by Coupling Superlattice and Quantum Wells." 2004. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-0707200421483100.
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Wang, Yuan-Chu, and 王源鉅. "Photovoltaic and Photoconductive Dual-mode Infrared Photodetector Made by Coupling Superlattice and Quantum Wells." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/41785236367502819530.
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碩士國立臺灣大學
電子工程學研究所
92
The infrared photodetectors are important in many civilian, military and scientific applications. Some of them, for example temperature sensing and target discrimination, requires the infrared photodetector to be equipped with the ability of multicolor detection. In this thesis, a new structure of superlattice infrared photodetector(SLIP) coupled to a quantum well infrared photoedetector (QWIP) is investigated. The SLIP is designed for wavelength 6~10µm detection while the QWIP is for wavelength around 11µm. The perspective is the photoresponse of 10µm from superlattice can couple to quantum wells under low bias with low dark current. The new structure can be operated under both photovoltaic and photoconductive mode. For the photovoltaic mode, three different photoresponse peaks from different transitions can be observed. It is believed that one peak is from SLIP and the other two are from QWIP. The lineshapes of the photoresponse will be changed with different temperature. As the temperature rising, the short wavelength photoresponses will be enhanced but the long wavelength ones are suppressed.The photovoltaic effect can be observed until 80K. For the photoconductive mode, because of the special structure, the photoresponse from SLIP is shown only under low negative bias. The perspective is the photoresponse from superlattice can couple to quantum wells under low negative bias and the photoresponse from both SLIP and QWIP can be observed simultaneously. In this way, we hope we can observe a broadband response. Based on this structure, our detector with photovoltaic and photoconductive dual-mode operation and properties of voltage-switchable and voltage-tunable can be achieved.
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Voigtmann, Thomas [Verfasser]. "Mode coupling theory of the glass transition in binary mixtures / Thomas Voigtmann." 2003. http://d-nb.info/967122414/34.
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Bhattacharyya, Sarika. "Extensions Of Mode Coupling Theory To Study Diffusion And Viscosity And Applications To Chemical Dynamics." Thesis, 1999. https://etd.iisc.ac.in/handle/2005/1598.
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