Orientadores: Stefano De Leo, Marcelo Moraes Guzzo / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-23T16:45:38Z (GMT). No. of bitstreams: 1 Maia_GabrielGulak_M.pdf: 1857100 bytes, checksum: 8af9898714b92a166704c01eafe1b9fa (MD5) Previous issue date: 2013 / Resumo: A interação de elétrons com barreiras de potencial é um problema bem conhecido da teoria quântica não-relativística de Schrödinger. O tratamento intrinsecamente relativístico do sistema, entretanto, por meio da teoria de Dirac, nos revela diferentes aspectos não fornecidos pela teoria precedente. Por exemplo, uma vez que a equação de Dirac contém naturalmente os graus de liberdade de spin, quatro coeficientes são necessários para descrever o processo e assim o fenômeno da inversão de spin, também chamado spin flip, surge. Com o objetivo de introduzir o formalismo teórico e a notação sobre a qual se sustenta este trabalho, o primeiro capítulo é dedicado a uma breve revisão da equação de Dirac, discutindo-se as propriedades de suas matrizes, a equação de continuidade e obtendo-se suas soluções livres. No capítulo 2 o sistema de interesse, a interação planar de partículas de Dirac com barreiras de potencial eletrostático, é apresentado e são destacados os aspectos que o diferenciam de seu equivalente não-relativístico. São definidos os potenciais escalar e eletrostático e as zonas cinemáticas estabelecidas para os casos unidimensional e bidimensional. O terceiro capítulo é reservado à obtenção dos coeficientes de reflexão e transmissão com e sem spin flip para partículas de Dirac difundindo planarmente através de uma barreira quadrada de potencial eletrostático. Este objetivo é alcançado através de dois métodos distintos de interpretações complementares: O método de degraus e o cálculo de barreira. Coeficientes não-nulos são obtidos para todos os casos, exceto para a transmissão através da barreira com inversão de spin, contrastando com o fato de que todos os degraus componentes da barreira apresentam coeficientes associados diferentes de zero. No quarto capítulo analisa-se o spin das partículas incidentes e o efeito da barreira sobre o spin das partículas refletidas. Ainda que o limite para baixas velocidades seja sempre 1/2, como esperado, em regimes relativísticos encontra-se uma dependência do valor médio deste operador com a energia e o ângulo de incidência no potencial. No quinto capítulo o formalismo de pacote de ondas é desenvolvido e a coerência dos pacotes em relação 'a barreira de potencial investigada, mostrando que a probabilidade de transmissão torna-se constante conforme a largura da barreira aumenta, o que caracteriza o regime incoerente de partículas. Ao fim do capítulo são derivadas as expressões para o spin incidente, refletido e transmitido nesse formalismo. Por fim, o sexto capítulo é reservado ao estudo introdutório do valor médio de autoestados do operador de spin através do formalismo desenvolvido no capítulo anterior como primeira mostra das possibilidades de trabalhos futuros. Mostrado que se o bispinor incidente não for um autoestado do Hamiltoniano de Dirac uma dependência temporal é verificada no valor médio / Abstract: The interaction of electrons with potential barriers is a well-known problem of the Schr¨odinger¿s non-relativistic quantum theory. The intrinsically relativistic treatment of the problem, however, through the Dirac¿s theory, reveals us different aspects, do not provided by the preceding theory. For instance, since the Dirac equation naturally contains the spinorial degree of freedom, four coefficients are needed in order to describe the process and so the spin flip phenomenon emerges. To introduce the theoretical formalism and the notation upon which this work is sustained, the first chapter is devoted to a short review of the Dirac equation, discussing the properties of its matrices, the continuity equation and obtaining its free solutions. Chapter 2 presents the system of interest, the planar interaction of Dirac particles with electrostatic potential barriers. It also highlights the aspects that differentiate this system from its non-relativistic analogue. The scalar and electrostatic potentials are defined and the kinematic zones established for the one-dimensional and the two-dimensional cases. The third chapter is reserved for obtaining the spin flip and spin conserving transmission and reflection coefficients for Dirac particles diffusing two-dimensionally through a square electrostatic potential barrier. This goal is achieved by means of two distinct methods of complementary interpretations: The barrier calculation and the steps calculation. Non-zero coefficients are obtained in all the cases except for the spin flip transmission, contrasting with the fact that no coefficient of the individual steps that compose the barrier is null. In the fourth chapter the incident particles¿ spin is analysed as well as the effect of the barrier on the spin of the reflected particles. As expected the low velocities limits gives us a spin value of 1/2 but in relativistic regime there is a dependence of the spin with the energy and the incidence angle into the potential. In the fifth chapter the wave packet formalism is developed and the packets¿ coherence is investigated, showing that the transmission probability becomes constant as the barrier width becomes greater, characterizing the incoherence of the particle limit. At the end of the chapter the expressions for the incident, reflected and transmitted spin in the new formalism are derived. Finally, the sixth chapter is reserved to the introductory study of mean values of the spin operator eigenstates through the formalism developed in the previous chapter as an example of possibilities for future investigations. It is shown that if the incident bispinor is not a Dirac Hamiltonian eigenstate there is a time dependence in the expected value. Key-words: Relativistic Quantum Mechanics, potential barriers, wave-packets / Mestrado / Física / Mestre em Física

Cette étude entend sonder la potentialité spéculative d'une philosophie éminemment kojèvienne qui naisse à partir de la relation entre le Désir et la Loi. Le privilège herméneutique accordé à ce plexus pour une enquête monographique de l'œuvre de Kojève vient de l'intuition d'une unité fondamentale dans sa pensée. Il s'agit de débuter une recherche sur la relation analysée à la lumière de la nouvelle ontologie que Kojève essaie de penser. Nous savons que Kojève est passé à l'histoire en tant que « interprète » de Hegel, en tant que doctor subtilis des légendaires Séminaires sur la Phénomélogie de l'Esprit. L'introduction à la lecture de Hegel a été le Livre-Evénement qui a affecté le Paris intellectuel des années Trente du XXème siècle et ses protagonistes de prestige ; mais fut uniquement la pointe de l'iceberg de la production scientifique de notre auteur. La reconstruction de I'opera omnia de Kojève, par conséquent, a été la base à partir de laquelle est devenue possible ce travail. À partir des écrits de la jeunesse émerge la matrice scientifique et, au même temps, spéculative de la réflexion kojèvienne : je fais référence au Journal d'un philosophe (1920-1923) et à l'idée du déterminisme dans la physique classique et dans la physique moderne (1932). La question, formulée en partie déjà de Kojève, est la suivante : c'est possible associer à la révolution quantique en physique la révolution psychanalytique en considérant que la détermination relative de la réalité physique implique et suppose l'existence de l'inconscient psychique ? Les observations préliminaires sur la science ont été fonctionnelles à donner une réponse affirmative à cette question et à présenter la généalogie de la thèse principale de ce travail : le sujet kojèvien n'est pas seulement - à la Butler - un sujet de désir ; mais, plutôt, un sujet de désir et loi. / This work seeks to explore the potential of the philosophy of Kojève, which has its offspring in the relation between Desire and Law. This plexus is regarded as the hermeneutic theme of the work of Kojève, based on the intuition of a fundamental unity within his thought.This study aims at starting a research about relationship, in the light of Kojève's nouvelle ontologie. Kojève is regarded as “the interpreter” of Hegel and the doctor subtilis of the legendary Seminars on the Phenomenology of Spirit. The Introduction à la lecture de Hegel was the work that revolutionised the scholars in Paris in the 1930s, but it was only the tip of the iceberg of the author's scientific production. Therefore, the reconstruction of the opera omnia of Kojève is the base of this work, which could not have been possible without it.The scientific and speculative roots of Kojève's thought are evident since the early works of the author, and particularly the Journal d'un philosophe (1920-1923) and l'idée du déterminisme dans la physique classique et dans la physique moderne (1932). The main question, partly formulated by Kojève himself, is the following: can we associate the quantic revolution in physics to the revolution of psychoanalysis, given that the relative determination of physic reality implies the existence of the psychological unconscious? The preliminary observations on science have been fundamental in order to give a positive answer to this question. They also represent the foundations of this research. According to Kojève, the subject is not simply, as Butler would hold, a subject of desire; but a subject of desire and law.

Relations between propagators and Green<p>functions of Hamiltonians which are SUSY partners have been obtained. New exact propagators for the family of multi-well, time-dependent and non-hermitian potentials have been calculated.<p><p>Non-conservative SUSY transformation has been studied in<p>the case of multichannel Schrodinger equation with different thresholds. Spectrum (bound/virtual states and resonances) of the<p>non-conservative SUSY partner of zero potential has been founded. <p><p>Exactly solvable model of the magnetic induced Feshbach resonance<p>has been constructed. This model was tested in the case of Rb$^{85}$.<p><p>Conservative SUSY transformations of the first and the second order have been studied in the case of multichannel Schrodinger equation with equal thresholds. Transformations which introduce non-trivial coupling between scattering channels have been founded. <p><p>The first order SUSY transformation which preserves $S$-matrix eigen-phase shifts and<p>modifies mixing parameter has been founded in the case of two channel scattering with partial waves of different parities. In the case of coinciding parities we have found the second order SUSY transformation which preserves $S$-matrix eigen-phase shifts and modifies mixing parameter. <p><p>Phenomenological two channel $^3S_1-^3D_1$<p>neutron-proton potential has been obtained by using single channel, phase equivalent and coupling SUSY transformations applied to zero potential. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

La mécanique quantique prédit l'existence de corrélations entre particules distantes qui ne peuvent s'expliquer dans le cadre des théories réalistes locales. Suite au développement récent de la théorie de l'information quantique, il a été réalisé que ces corrélations non-locales ont des implications quant aux capacités de traitement de l'information des systèmes quantiques. Outre une signification physique, elles possèdent donc une signification informationnelle. Cette thèse traite de différents aspects de la non-localité liés à ces deux facettes du phénomène.<p><p>Nous commençons par un examen de la structure des corrélations locales et non-locales. Nous dérivons dans ce contexte de nouvelles inégalités de Bell, et généralisons ensuite le paradoxe de Greenberger-Horne-Zelinger à des états quantiques de dimension arbitraire et composés de plusieurs sous-systèmes. <p><p>Nous abordons par après la non-localité du point de vue de la théorie de l'information. Il est possible de concevoir des théories non-locales consistantes avec le principe de causalité mais offrant des avantages supérieurs à la mécanique quantique en terme de manipulation de l'information. Nous investiguons l'ensemble des corrélations compatibles avec de telles théories afin d'éclairer l'origine des limitations imposées par le formalisme quantique. Nous nous intéressons également à la quantité de communication classique nécessaire pour simuler les corrélations non-locales. Nous montrons que cette mesure naturelle de la non-localité est étroitement liée au degré de violations des inégalités de Bell.<p><p>Nous nous tournons ensuite vers des aspects expérimentaux. La faible efficacité des détecteurs utilisés dans les expériences de violation des inégalités de Bell reste un obstacle majeur à une démonstration convaincante de la non-localité, mais aussi à toute utilisation de la non-localité dans des protocoles d'information quantique. Nous dérivons d'une part des bornes quant à l'efficacité minimale requise pour violer les inégalités de Bell, et d'autre part des exemples de corrélations plus résistante à ces imperfections expérimentales. <p><p>Finalement, nous clôturons cette thèse en montrant comment la non-localité, principalement étudiée dans le cadre de systèmes décrits par des variables discrètes, telles que les variables de spin, peut également se manifester dans des systèmes à variables continues, telles que les variables de position et d'impulsion.<p> / Doctorat en sciences, Spécialisation physique / info:eu-repo/semantics/nonPublished

M.Sc. (Applied Mathematics) / Entanglement is a quantum resource with applications in quantum communication as well as quantum computing amongst others. Since quantum entanglement is such an abstract concept numerous mathematical measures exist. Some of these have a purely theoretic purpose whereas others play a role in describing the magnitude of entanglement of a system. In quantum systems energy level crossing may occur. Energy levels in quantum systems tend to repel each other so when any type of degeneracy occurs where the energy levels coalesce or cross it is of interest to us. Two such points of degeneracy are exceptional and diabolic points. When these occur it is useful to investigate these points in specific systems and observe level crossing. In this thesis we mainly investigate the relationship between entanglement, energy level crossing and symmetry as well as the exceptional and diabolic points of specific systems. We are especially interested in systems described by spin and Fermi operators.

La thèse vise à montrer que la cohérence de l’interprétation instrumentaliste de la mécaniquequantique (sur laquelle les reconstructions logiques de la théorie, d’inspiration pragmatiste, s’appuient) ne peut pas être défendue sans remettre en cause la sémantique extensionnelle utilisée en logique classique. J’examine en particulier les arguments misen avant par Niels Bohr, en montrant que son analyse physique du processus de mesureest insuffisante pour assurer la cohérence de l’interprétation conditionnelle des probabilités quantiques qu’il adopte. Au lieu d’essayer de ‘compléter’ l’approche de Bohrpar un compte rendu plus exhaustif des processus physiques (telle la décohérence) quijouent un rôle dans l’observation, je suggère que le problème de la mesure découle d’unethéorie de la signification inadéquate. Je discute l’intérêt et les limites de la critiquebohrienne des présupposés représentationalistes inhérents à la description classique desphénomènes, et je conclus en formulant l’hypothèse que l’adoption d’une sémantiqueinférentialiste permettrait d’envisager à la fois la dissolution du problème de la mesureet la justification a priori des traits structuraux des probabilités quantiques (comme étantl’expression des relations conceptuelles présupposées par tout langage qui doit incluredes énoncés objectifs). / The dissertation purports to show that the consistency of the instrumentalist interpretationof quantum mechanics (upon which the logico-operational reconstructions of thetheory rest) cannot be defended without relinquishing the extensional semantic frameworkof classical logic. I examine in particular Niels Bohr’s argument, arguing that hisphysical analysis of measurement is insufficient to establish the coherence of the conditionalconstrual of quantum probabilities that he advocates. Rather than attemptingto ‘complete’ Bohr’s approach by means of a more sophisticated and comprehensiveaccount of the physical processes involved in the act of observation (e.g., decoherence),I suggest that the measurement problem should be viewed as the outgrowth of an inadequatetheory of meaning. I discuss, and point out some limitations of, Bohr’s ownpioneering critique of the representational assumptions inherent to the classical accountof phenomena, and I conclude by suggesting that the endorsement of an inferentialistsemantic approach would not only contribute to defusing the measurement problem, butmight also enable the a priori justification of the structural features of quantum probability(in terms of the conceptual relations presupposed by any language which allowsfor objective assertions).

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Photonics, the technological field that encompasses all aspects of light, has been rapidly growing and increasingly useful in uncovering fundamental truths about nature. It has helped detect gravitational waves, allowed for a direct measurement of the quantum wave function, and has helped realize the coldest temperatures in the universe. But photonics has also had an enormous impact on day-to-day life as well; it has enabled high capacity and/or high speed telecommunication, offered cancer treatment solutions, and has completely revolutionized display and scanning technology. All of these discoveries and applications have required a superb understanding of light, but also a high degree of control over the sometimes abstract properties of light. The work contained in this thesis explores two novel means of controlling and manipulating two different abstract properties of light. In Part I, the property under investigation is the polarization state of light – a property that is paramount to all light-matter interactions, and even some light-light interactions such as interference. Here, a liquid crystal on silicon spatial light modulator (LCOS-SLM)’s capabilities in manipulating the polarization state of light is theoretically examined and experimentally exploited, tested, and reported on. It is found through experimentation that, for an appropriate range of beam sizes and input polarizations, a single LCOS-SLM can be used to produce any light field with an arbitrary, spatially varying polarization profile. In Part II, the property under investigation loosely corresponds to light’s spatial degree of freedom – how light can move from one spot in space to another in a non-trivial manner. Here, control over light’s position through a waveguide array through the use of quantum geometric phase is theoretically examined, simulated, and experimentally designed. It is found through simulation that a threewaveguide array is capable of implementing two dimensional unitary transformations. The common theme between Part I and Part II is manipulating these properties of light to realize classes of general transformations. Moreover, if the light field is treated as a quantum state in the basis of either property under investigation, a two dimensional computational basis ensues. This is precisely the right cardinality for applications in quantum information.

Wave phenomena appear in many fields of science such as acoustics, geophysics, and quantum mechanics. They can often be described by partial differential equations (PDEs). As PDEs typically are too difficult to solve by hand, the only option is to compute approximate solutions by implementing numerical methods on computers. Ideally, the numerical methods should produce accurate solutions at low computational cost. For wave propagation problems, high-order finite difference methods are known to be computationally cheap, but historically it has been difficult to construct stable methods. Thus, they have not been guaranteed to produce reasonable results. In this thesis we consider finite difference methods on summation-by-parts (SBP) form. To impose boundary and interface conditions we use the simultaneous approximation term (SAT) method. The SBP-SAT technique is designed such that the numerical solution mimics the energy estimates satisfied by the true solution. Hence, SBP-SAT schemes are energy-stable by construction and guaranteed to converge to the true solution of well-posed linear PDE. The SBP-SAT framework provides a means to derive high-order methods without jeopardizing stability. Thus, they overcome most of the drawbacks historically associated with finite difference methods. This thesis consists of three parts. The first part is devoted to improving existing SBP-SAT methods. In Papers I and II, we derive schemes with improved accuracy compared to standard schemes. In Paper III, we present an embedded boundary method that makes it easier to cope with complex geometries. The second part of the thesis shows how to apply the SBP-SAT method to wave propagation problems in acoustics (Paper IV) and quantum mechanics (Papers V and VI). The third part of the thesis, consisting of Paper VII, presents an efficient, fully explicit time-integration scheme well suited for locally refined meshes.

The main aim of this thesis was to create a set of problems in Quantum Mechanics, which would be included in a collection of solved problems in Physics available online on the website http://www.fyzikalniulohy.cz. As a result, thirty nine problems were completed, covering seven thematic areas partially of high school and mostly of introductory college Quantum Mechanics course. In general, the collection is mainly designed for college students as an exercise in basic quantum-mechanical problems and also for high school students, who have a desire to deal with some special problems. A detailed description of content, structure, and technical execution of this collection can be found in chapter 1 of this thesis. Another task was to review existing online collections of applets dealing with Quantum Mechanics. A selection of them is introduced in chapter 2 of this thesis.