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Дисертації з теми "5108 Quantum physics"

Автор: Grafiati

Опубліковано: 10 січня 2023

Оновлено: 28 січня 2023

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1

Stevens, Neil. "Concepts surrounding incompatibility in quantum physics." Thesis, University of York, 2014. http://etheses.whiterose.ac.uk/8277/.

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This thesis concerns how attempting to measure certain fundamental properties of a physical theory can lead us to new insights. The idea of general probabilistic models is introduced and developed, in order to provide a way to be able to consider and compare different theories. A measure of incompatibility of two observables is defined, through the amount of smearing needed to make them jointly measureable. This measure is then used to characterise the degree of incompatibility that exists in a given theory. Quantum theory is then shown to be as incompatible as any other theory, but only in a very course grained sense. A related way of measuring the strength of incompatibility of a pair of observables is then shown to put a bound on a measure of the strength of non-local correlations. The notion of steering, or remote ensemble preparation, is then shown to be a sufficient condition for the saturation of that bound. Examples are considered that demonstrate that the given sufficient notion of steering is not necessary, and it is proposed how the measures can be modified in cases where the link does not hold. The idea of formulating measures of error and disturbance associated with a measurement device is discussed. The notion of a direct test of error or disturbance is used to analyse current proposed measures, and show their shortcomings.

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2

Benassi, Costanza. "On classical and quantum lattice spin systems." Thesis, University of Warwick, 2018. http://wrap.warwick.ac.uk/108566/.

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This thesis focuses on some results about quantum and classical lattice spin systems. We study a wide class of two-dimensional quantum models which enjoy a U(1) symmetry. Using the so called complex rotation method we show that the decay of the relevant correlation functions is at least algebraically fast. We provide some examples of relevant models which belong to our class. We review some results present in the literature concerning the so called GriffthsGinibre inequalities for the classical XY model and propose a generalisation to its quantum counterpart. Correlation inequalities indeed hold for the quantum XY model with spin- 1 2 and for the ground state of the spin-1 system. We propose some applications of these results, namely that the infinite volume limit of some correlation functions exists and that it is possible to compare quenched and annealed averages for a quantum XY model with random couplings. We investigate loop representations for O(n) classical spin systems. We propose a generalised random current representation and show its relationship with the Brydges-Fröhlich-Spencer one. We review some conjectures regarding the expected behaviour of these loop models { namely that macroscopic loops appear and their lengths are distributed according to a Poisson-Dirichlet distribution. We propose some arguments in favour of these conjectures for O(n) loop models, using a mix of exact results and heuristic considerations. In order to do so we de ne a stochastic process which is an effective split-merge process for macroscopic loops and we reformulate some correlation functions for the O(2) spin system in terms of loop properties.

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3

Hollands, Stefan. "Aspects of quantum field theory in curved spacetime." Thesis, University of York, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325670.

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4

Gütschow, Johannes [Verfasser]. "Quantum information processing with Clifford quantum cellular automata / Johannes Gütschow." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2013. http://d-nb.info/1033705470/34.

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5

Feiler, Cornelia [Verfasser]. "Quantum physics and number theory connected by the Riemann zeta function / Cornelia Feiler." Ulm : Universität Ulm. Fakultät für Naturwissenschaften, 2014. http://d-nb.info/1049561953/34.

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6

Waldherr, Konrad [Verfasser]. "Numerical Linear and Multilinear Algebra in Quantum Control and Quantum Tensor Networks / Konrad Waldherr." München : Verlag Dr. Hut, 2014. http://d-nb.info/1064560601/34.

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7

Werner, Albert H. [Verfasser]. "Localization and recurrence in quantum walks / Albert H. Werner." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2013. http://d-nb.info/1046028499/34.

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8

Wrazidlo, Dominik [Verfasser], and Markus [Akademischer Betreuer] Banagl. "Fold maps and positive topological quantum field theories / Dominik Wrazidlo ; Betreuer: Markus Banagl." Heidelberg : Universitätsbibliothek Heidelberg, 2017. http://d-nb.info/1178009157/34.

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9

Toussaint, Vladimir. "Particle detectors in fermionic and bosonic quantum field theory in flat and curved spacetimes." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/49473/.

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This thesis is concerned with aspects of quantum theory of fields in flat and curved spacetimes of arbitrary dimensions along with detecting bosons and fermions on these spacetimes. The thesis is divided into two main parts. In the first part, we analyse an Unruh-DeWitt particle detector that is coupled linearly to the scalar density of a massless Dirac field (neutrino field) in Minkowski spacetimes of dimension d ≥ 2 and on the two-dimensional static Minkowski cylinder, allowing the detector’s motion to remain arbitrary and working to leading order in perturbation theory. In d-dimensional Minkowski spacetime, with the field in the usual Fock vacuum, we show that the detector’s response is identical to that of a detector coupled linearly to a massless scalar field in 2d-dimensional Minkowski. In the special case of uniform linear acceleration, the detector’s response hence exhibits the Unruh effect with a Planckian factor in both even and odd dimensions, in contrast to the Rindler power spectrum of the Dirac field, which has a Planckian factor for odd d but a Fermi-Dirac factor for even d. On the two-dimensional cylinder, we set the oscillator modes in the usual Fock vacuum but allow an arbitrary state for the zero mode of the periodic spinor. We show that the detector’s response distinguishes the periodic and antiperiodic spin structures, and the zero mode of the periodic spinor contributes to the response by a state-dependent but well defined amount. Explicit analytic and numerical results on the cylinder are obtained for inertial and uniformly accelerated trajectories, recovering the d = 2 Minkowski results in the limit of large circumference. The detector’s response has no infrared ambiguity for d = 2, neither in Minkowski nor on the cylinder. In the second part, firstly, we give a thorough discussion for the Bogolubov transformation for Dirac field, and discuss pair creation in a non-stationary spacetime. Secondly, we derive the in and out vacua Wightman two-point functions for the Dirac field and the Klein-Gordon field for certain class of spatially flat Friedmann-Robertson-Walker (FRW) cosmological spacetimes wherein the two-point functions have the Hadamard form. We then establish the equivalence between the adiabatic vacuum of infinite order and the conformal vacuum in the massless limit. With the field in the conformal Fock vacuum, we then show that the detector’s response to an UDW particle detector coupled linearly to the scalar density of a massless Dirac field in the spatially flat FRW spacetimes in d-dimensions is identical to the response of a detector coupled to the massless scalar field in the spatially flat FRW spacetimes in 2d-dimensions. Lastly, we discuss a massive scalar field in the spatially compactified (1 + 1)-dimensional FRW spacetime. There, the issue of the conformal zero momentum mode arises. To resolve this issue, we develop a new scheme for quantizing the conformal zero-mode. This new quantization scheme introduces a family of two real parameters for every zero-momentum mode with an associated two-real-parameter set of in/out vacua. We then show that the zero momentum initial state’s wave functional corresponds to a two-real parameter set of Gaussian wave packets. For applications, we examine the finite-time detector’s response to a massive scalar field in the (1 + 1)-dimensional, spatially compactified Milne spacetime. Explicit analytic results are obtained for the comoving and inertially non-comoving trajectories. Numerical results are provided for the comoving trajectory. The numerical results suggest that when the in-vacuum is chosen to be very far from the conventional Minkowski vacuum state, then it contains particles. As result, spontaneous excitation of the comoving detector occurs.

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10

Elsayed, Tarek A. [Verfasser], and Boris [Akademischer Betreuer] Fine. "Chaos and Relaxation in Classical and Quantum Spin Systems / Tarek A. Elsayed ; Betreuer: Boris Fine." Heidelberg : Universitätsbibliothek Heidelberg, 2013. http://d-nb.info/1177382822/34.

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11

Peschutter, Jochen Christian [Verfasser], Thomas [Gutachter] Quella, and Martin R. [Gutachter] Zirnbauer. "Quantum Superspin Systems from Conformal Field Theory / Jochen Christian Peschutter ; Gutachter: Thomas Quella, Martin R. Zirnbauer." Köln : Universitäts- und Stadtbibliothek Köln, 2016. http://d-nb.info/1130322947/34.

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12

Ferguson, James. "Geometric structures on the target space of Hamiltonian evolution equations." Thesis, Connect to e-thesis, 2008. http://theses.gla.ac.uk/206/.

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Thesis (Ph.D.) - University of Glasgow, 2008.
Ph.D. thesis submitted to the Faculty of Information and Mathematical Sciences, Department of Mathematics, 2008. Includes bibliographical references. Print version also available.

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13

Hihn, Markus. "The generalized chord diagram expansion." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17592.

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Dyson-Schwinger-Gleichungen sind Fixpunktgleichungen, die in der Quantenfeldtheorie auftauchen. Obwohl es bekannt ist, wie die Kombinatorik vor der Anwendung von Feynman-Regeln aussieht, war die Kombinatorik der resultierenden analytischen Dyson-Schwinger-Gleichungen bisher unbekannt. Wir verallgemeinern die Arbeiten von Yeats et.al. auf diesem Gebiet zu einer Klasse von unendlich vielen Dyson-Schwinger-Gleichungen mit Hilfe von Sehnen-Diagrammen.
In quantum field theory, Dyson-Schwinger equations are fixed-point equations that come from self insertion properties of Feynman graphs. While the combinatorics of these are well understood, the combinatorics are still mysterious after applying the Feynman rules. We generalize the work of Yeats et.al. in this field to an infinite number of Dyson-Schwinger equations with the help of chord diagrams.

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14

Rousse, François. "Algorithmes incrémentaux pour la théorie de la fonctionnelle de la densité sans orbitale." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAM039.

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L'informatique est devenue un outil incontournable de la chimie. En effet la capacité de simuler des molécules sur ordinateur a aidé à la compréhension du monde nanoscopic et à la prédiction de ses propriétés. La simulation moléculaire a eu ces dernières décennies un impact scientifique énorme en biologie, en électronique, en science des matériaux … La simulation de particules est une des méthodes classiques de dynamique moléculaire, les molécules y sont divisées en atomes, leurs interactions relatives calculées et leurs trajectoires déduites pas à pas. Malheureusement un calcul précis des interactions entre atomes demande énormément d'opérations et donc de temps, ce qui limite la portée de la simulation moléculaire à des systèmes de taille raisonnable. C'est dans ce contexte que notre équipe recherche de nouveaux modèles de simulation moléculaire rapide et précis. Un des angles de recherche est l'élimination des calculs inutiles des simulations. L'équipe a ainsi proposé un modèle de dynamique moléculaire dite restreinte de manière adaptative dans lequel le mouvement des particules les plus lentes est bloqué. Si la simulation ne recalcule pas les interactions inchangées entre atomes bloqués, le calcul des interactions est plus rapide. L'équipe a aussi développé plusieurs modèles d'interactions plus efficaces pour des modèles de dynamique restreinte de particules, ils mettent à jour les interactions de façon incrémentale en utilisant les résultats du pas de temps précédent et la liste des particules mobiles.Dans le sillage des travaux de notre équipe de recherche, nous proposons dans cette thèse une méthode incrémentale pour calculer des interactions interatomique basées sur les modèles de Théorie de la Fonctionnelle de la Densité Sans Orbitale. La nouvelle méthode garde les calculs dans l'espace réel et peut ainsi concentrer les calculs où cela est nécessaire. Dans ce manuscrit nous vérifions cette méthode, puis nous évaluons les gains de vitesse lorsqu'une majorité de particule est bloquée, avec un modèle de dynamique restreinte. Ces travaux sont un pas vers la l'intégration de modèles d'interactions Premier-principes pour des modèles dynamiques restreint de manière adaptative
The ability to model molecular systems on a computer has become a crucial tool for chemists. Molecular simulations have helped to understand and predict properties of nanoscopic world, and have had large impact on domains like biology, electronic or materials development. Unfortunately, inter-atomic interactions computation costs prevent large systems to be modeled in a reasonable time. In this context, our research team looks for new accurate and efficient molecular simulation models. One of our team's focus is the search and elimination of useless calculus in dynamical simulations, hence has proposed a new adaptively restrained dynamical model that freezes the slowest particles movement and several interaction models that benefit from a restrained dynamical model by updating interaction incrementally.In the wake of our team's work, we propose in this thesis an incremental First-principles interaction models. Precisely, we have developed an incremental Orbital-Free Density Functional Theory method that benefits from an adaptively restrained dynamical model. The new method is first proof-tested, then we show its ability to speed up computations when a majority of particle are static and hence with a restrained particle dynamic model. This work is a first step toward a combination of incremental First-principle interaction models and adaptively restrained particular dynamic models

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15

Mai, The Tien. "PAC-Bayesian estimation of low-rank matrices." Electronic Thesis or Diss., Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLG001.

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Les deux premi`eres parties de cette th`ese 'etudient respectivement des estimateurs pseudo-bay'esiens dans les probl`emes de compl'etion de matrices, et de tomographie quantique. Dans chaque probl`eme, on propose une loi a priori qui induit des matrices de faible rang. On 'etudie les performances statistiques: dans chacun des deux cas, on prouve des vitesses de convergence pour nos estimateurs. Notre analyse repose essentiellement sur des in'egalit'es PAC-Bay'esiennes. On propose aussi un algorithme MCMC pour impl'ementer notre estimateur. On teste ensuite ses performances sur des donn'ees simul'ees, et r'eelles. La derni`ere partie de la th`ese 'etudie le probl`eme de lifelong learning (que l'on peut traduire par apprentissage au long cours), o`u de l'information est conserv'ee et transf'er'ee d'un probl`eme d'apprentissage `a un autre. Nous proposons une formalisation de ce probl`eme dans un contexte de pr'ediction s'equentielle. Nous proposons un m'eta-algorithme pour le transfert d'information, qui repose sur l'agr'egation `a poids exponentiels. On prouve une borne sur le regret de cette m'ethode. Un avantage important de notre analyse est qu'elle ne requiert aucune hypoth`ese sur la forme des algorithmes d'apprentissages utilis'es `a l'int'erieur de chaque probl`eme. On termine cette partie par l''etude de quelques exemples: cas d'un nombre fini de pr'edicteurs, apprentissage d'une direction r'ev'elatrice, et apprentissage d'un dictionnaire
The first two parts of the thesis study pseudo-Bayesian estimation for the problem of matrix completion and quantum tomography. A novel low-rank inducing prior distribution is proposed for each problem. The statistical performance is examined: in each case we provide the rate of convergence of the pseudo-Bayesian estimator. Our analysis relies on PAC-Bayesian oracle inequalities. We also propose an MCMC algorithm to compute our estimator. The numerical behavior is tested on simulated and real data sets. The last part of the thesis studies the lifelong learning problem, a scenario of transfer learning, where information is transferred from one learning task to another. We propose an online formalization of the lifelong learning problem. Then, a meta-algorithm is proposed for lifelong learning. It relies on the idea of exponentially weighted aggregation. We provide a regret bound on this strategy. One of the nice points of our analysis is that it makes no assumption on the learning algorithm used within each task. Some applications are studied in details: finite subset of relevant predictors, single index model, dictionary learning

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16

Celalettin, Metin. "‘A quantum observation technique; Quantum decoherence-by-depolarisation-tunnelling in a Spin Polarized Electron Gas, described by ‘Celalettin’s 1st Paradigm’’." Thesis, 2021. https://vuir.vu.edu.au/43943/.

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A Spin Polarized Electron Gas (SPEG) will be mathematically modelled to provide a medium in which the phenomenon will occur. Drawing on similar models consistent with the Quantum Monte Carlo (QMC) method, it will result in an equation enabling the medium to leave evidence of a foreign particle attempting to tunnel through it. This meets the objective of this study, quantum measurement. The SPEG’s spin exchange energy boundaries and collective electric dipole spin frequencies will enable the required Free Electron Laser (FEL) to be calibrated to the SPEG frequency forming the crux of the proposal. The mathematical model will leverage off investigations that have been performed at the single electron level, such as precession manipulation and application to a SPEG. This research will then present a formula that describes a SPEG pierced by a FEL and producing a resultant tunnel; its walls stoned by spin-flipped electrons. The formula presented will be the energy expression of the tunnel by depolarization.

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17

Müller, Markus [Verfasser]. "Quantum Kolmogorov complexity and the Quantum Turing Machine / vorgelegt von Markus Müller." 2007. http://d-nb.info/985912529/34.

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18

Lessel, Bernadette. "Shape space in terms of Wasserstein geometry and application to quantum physics." Doctoral thesis, 2018. http://hdl.handle.net/11858/00-1735-0000-002E-E512-4.

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19

Sadel, Christian [Verfasser]. "Analysis of random matrix actions related to random operators in quantum physics / vorgelegt von Christian Sadel." 2009. http://d-nb.info/997267313/34.

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20

Fritz, Tobias [Verfasser]. "Contributions to quantum probability / vorgelegt von Tobias Fritz." 2010. http://d-nb.info/1007090731/34.

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21

Tsouchnika, Efrossini [Verfasser]. "Quantum groups and field theory / von Efrossini Tsouchnika." 2008. http://d-nb.info/990040739/34.

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22

Rama, Juliane [Verfasser]. "Time evolution of quantum resonance states / von Juliane Rama." 2007. http://d-nb.info/987249398/34.

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23

Ha, Eugene [Verfasser]. "Quantum statistical mechanics of Shimura varieties / vorgelegt von Eugene Ha." 2006. http://d-nb.info/980749964/34.

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24

Khalique, Aeysha [Verfasser]. "Robustness bounds and practical limitations of quantum key distribution / von Aeysha Khalique." 2008. http://d-nb.info/993850340/34.

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25

Volkert, Georg Friedrich [Verfasser]. "Tensor fields on orbits of quantum atates and applications / vorgelegt von Georg Friedrich Volkert." 2010. http://d-nb.info/1005567808/34.

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26

Dhamo, Elidon [Verfasser]. "Dispersive effects in quantum kinetic equations : the Wigner-Poisson-Fokker-Planck system / Elidon Dhamo." 2006. http://d-nb.info/991233867/34.

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27

Döring, Andreas [Verfasser]. "Stone spectra of von Neumann algebras and foundation of quantum theory / von Andreas Döring." 2005. http://d-nb.info/97444328X/34.

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28

Steiner, Lisa [Verfasser]. "A C*-algebraic approach to quantum coding theory / von Lisa Steiner." 2008. http://d-nb.info/993822096/34.

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29

Schubert, Katrin [Verfasser]. "Quantum Markov chains and position distributions for states of boson systems / vorgelegt von Katrin Schubert." 2005. http://d-nb.info/976683504/34.

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30

Liu, Qingzhe [Verfasser]. "Solutions to the multi-dimensional viscous quantum hydrodynamic equations for semiconductors / vorgelegt von Qingzhe Liu." 2009. http://d-nb.info/995904464/34.

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31

Jansen, Sabine [Verfasser]. "Laughlin's wave function, plasma analogies and the fractional quantum Hall effect on infinite cylinders / vorgelegt von Sabine Jansen." 2007. http://d-nb.info/985159480/34.

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32

Wrochna, Michal. "Singularities of two-point functions in Quantum Field Theory." Doctoral thesis, 2013. http://hdl.handle.net/11858/00-1735-0000-0001-BB3C-E.

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33

MAI, The Tien. "PAC-Bayesian estimation of low-rank matrices." Thesis, 2017. http://www.theses.fr/2017SACLG001/document.

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Анотація:

Les deux premi`eres parties de cette th`ese 'etudient respectivement des estimateurs pseudo-bay'esiens dans les probl`emes de compl'etion de matrices, et de tomographie quantique. Dans chaque probl`eme, on propose une loi a priori qui induit des matrices de faible rang. On 'etudie les performances statistiques: dans chacun des deux cas, on prouve des vitesses de convergence pour nos estimateurs. Notre analyse repose essentiellement sur des in'egalit'es PAC-Bay'esiennes. On propose aussi un algorithme MCMC pour impl'ementer notre estimateur. On teste ensuite ses performances sur des donn'ees simul'ees, et r'eelles. La derni`ere partie de la th`ese 'etudie le probl`eme de lifelong learning (que l'on peut traduire par apprentissage au long cours), o`u de l'information est conserv'ee et transf'er'ee d'un probl`eme d'apprentissage `a un autre. Nous proposons une formalisation de ce probl`eme dans un contexte de pr'ediction s'equentielle. Nous proposons un m'eta-algorithme pour le transfert d'information, qui repose sur l'agr'egation `a poids exponentiels. On prouve une borne sur le regret de cette m'ethode. Un avantage important de notre analyse est qu'elle ne requiert aucune hypoth`ese sur la forme des algorithmes d'apprentissages utilis'es `a l'int'erieur de chaque probl`eme. On termine cette partie par l''etude de quelques exemples: cas d'un nombre fini de pr'edicteurs, apprentissage d'une direction r'ev'elatrice, et apprentissage d'un dictionnaire
The first two parts of the thesis study pseudo-Bayesian estimation for the problem of matrix completion and quantum tomography. A novel low-rank inducing prior distribution is proposed for each problem. The statistical performance is examined: in each case we provide the rate of convergence of the pseudo-Bayesian estimator. Our analysis relies on PAC-Bayesian oracle inequalities. We also propose an MCMC algorithm to compute our estimator. The numerical behavior is tested on simulated and real data sets. The last part of the thesis studies the lifelong learning problem, a scenario of transfer learning, where information is transferred from one learning task to another. We propose an online formalization of the lifelong learning problem. Then, a meta-algorithm is proposed for lifelong learning. It relies on the idea of exponentially weighted aggregation. We provide a regret bound on this strategy. One of the nice points of our analysis is that it makes no assumption on the learning algorithm used within each task. Some applications are studied in details: finite subset of relevant predictors, single index model, dictionary learning

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