Tesi sul tema "Disordered quantum systems"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Disordered quantum systems".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
Kropf, Chahan [Verfasser], e Andreas [Akademischer Betreuer] Buchleitner. "Effective dynamics of disordered quantum systems". Freiburg : Universität, 2017. http://d-nb.info/1138922528/34.
Mukhopadhyay, Ranjan Goodstein David L. "Quantum phase transitions in disordered Bose systems /". Diss., Pasadena, Calif. : California Institute of Technology, 1998. http://resolver.caltech.edu/CaltechETD:etd-02022007-104407.
Schwab, David Jason. "Topics in biophysics and disordered quantum systems". Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1971489301&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
Nahm, In Hyun. "Two dimensional disordered electron systems". Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330179.
Goswami, Pallab. "Quantum phase transitions in dissipative and disordered systems". Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1680035131&sid=4&Fmt=2&clientId=1564&RQT=309&VName=PQD.
Ros, Valentina. "Aspects of localization in disordered many-body quantum systems". Doctoral thesis, SISSA, 2016. http://hdl.handle.net/20.500.11767/4906.
Bapst, Victor. "Quantum disordered systems : from adiabatic computation to localization problems". Paris 6, 2013. http://www.theses.fr/2013PA066351.
Cette thèse est consacrée à l'étude de systèmes désordonnés quantiques, avec des applications allant de la localisation d'Anderson au calcul quantique. Nous nous concentrons sur des modèles définis sur des arbres, ou sur leurs régularisations de taille finie: les graphes aléatoires. Sur ces modèles, les approches de champ moyen sont exactes. La première partie s'intéresse au problème de la localisation d'Anderson. Nous obtenons des résultats analytiques sur la décroissance rapide de la densité d'états près de son bord (le régime de la queue de Lifshitz), ainsi qu'une estimation rigoureuse du seuil de localisation dans la limite de grande connectivité. Nous étudions aussi le problème analogue dans le cas de bosons. Dans une second partie, nous étudions l'algorithme adiabatique quantique et obtenons des résultats sur sa capacité à résoudre un problème réaliste, celui du coloriage, ainsi que des prédictions analytiques sur ses performances pour résoudre des problèmes plus généraux. Enfin, nous discutons également comment cet algorithme quantique se compare à une approximation classique de ce dernier
Ludwig, Thomas. "Interaction and phase relaxation in disordered nanowires and quantum hall systems". Karlsruhe : FZKA, 2006. http://bibliothek.fzk.de/zb/berichte/FZKA7204.pdf.
Semerjian, Guilhem. "Mean-field disordered systems : glasses and optimization problems, classical and quantum". Habilitation à diriger des recherches, Ecole Normale Supérieure de Paris - ENS Paris, 2013. http://tel.archives-ouvertes.fr/tel-00785924.
Grabsch, Aurélien. "Random Matrix Theory in Statistical Physics : Quantum Scattering and Disordered Systems". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS142/document.
Random matrix theory has applications in various fields: mathematics, physics, finance, ... In physics, the concept of random matrices has been used to study the electronic transport in mesoscopic structures, disordered systems, quantum entanglement, interface models in statistical physics, cold atoms, ... In this thesis, we study coherent AC transport in a quantum dot, properties of fluctuating 1D interfaces on a substrate and topological properties of multichannel quantum wires. The first part gives a general introduction to random matrices and to the main method used in this thesis: the Coulomb gas. This technique allows to study the distribution of observables which take the form of linear statistics of the eigenvalues. These linear statistics represent many relevant physical observables, in different contexts. This method is then applied to study concrete examples in coherent transport and fluctuating interfaces in statistical physics. The second part focuses on a model of disordered wires: the multichannel Dirac equation with a random mass. We present an extension of the powerful methods used for one dimensional system to this quasi-1D situation, and establish a link with a random matrix model. From this result, we extract the density of states and the localization properties of the system. Finally, we show that this system exhibits a series of topological phase transitions (change of a quantum number of topological nature, without changing the symmetries), driven by the disorder
Goldsborough, Andrew M. "Tensor networks and geometry for the modelling of disordered quantum many-body systems". Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/70003/.
Schneider, Michael Peter. "A theoretical framework for waveguide quantum electrodynamics and its application in disordered systems". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17415.
Waveguide quantum electrodynamics (waveguide QED) can be considered as a building block for many prospective technologies like quantum computing. A prototypical system consists of a two-level system (TLS) coupled to a one-dimensional waveguide. The waveguide is characterized by its dispersion relation and can also feature a band edge/slow-light regime. In this thesis we have presented a new theoretical framework for waveguide QED, based on quantum field theory. The framework provides the Green''s functions of the system in the single- and two-excitation sectors for an arbitrary dispersion relation. We have calculated the scattering matrix and the spectral density in both sectors. Furthermore, we have also represented the Green''s functions in the form of Feynman diagrams, from which we can identify the underlying physical processes. A special property of the system is that it behaves nonlinear in the case of two or more photons. This is rooted in the structure of the TLS, which can at most absorb one excitation. The nonlinearity leads to two effects: photon bunching and the efficient excitation of an atom-photon bound state. We have found both effects within our framework and we were able to assign them individual terms in the perturbation series of the Green''s function. Furthermore, we have used the Green''s function in space-time domain to propagate Gaussian one- and two-photon wavepackets. Here, we have identified the ratio of the pulsewidth and the spontaneous emission time as the parameter which governs both the scattering behavior of the photons and the maximal TLS excitation. Eventually, we have investigated the effects of disorder in the waveguide on the decay properties of the TLS. We have found here that the atom-photon bound state is stable for small disorder, but breaks down at sufficiently strong disorder. Furthermore, we have identified a special class of diagrams which render the system non-Markovian even for energies far away from the band edge.
Yan, Mi. "Quantum Dynamics of Strongly-Interacting Bosons in Optical Lattices with Disorder". Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/87432.
Ph. D.
Ultracold atoms in optical lattices, a periodic potential generated by laser beams, offer an important tool for quantum simulations in a pristine environment. Motivated by recent optical lattice experiments with the implementation of disorder and synthetic spin-orbit coupling, we utilize Gutzwiller mean-field theory (GMFT) to study the dynamics of disordered state in an optical lattice under the sudden shift of the harmonic trap, the domain wall expansion of strongly interacting bosons in 2D lattices with disorder, and spin-orbit-driven transitions in the Bose-Hubbard model. We argue that the center of mass velocity can aid in identifying a Bose-glass phase. Our findings show that evidence for many-body localization claimed in experiments [J.-y. Choi et al., Science 352, 1547 (2016)] must lie in the differences between GMFT and experiments. We also find that strong spin-orbit coupling alone can generate superfluids with finite momentum and staggered phase patterns.
Karevski, Dragi. "Ising Quantum Chains". Habilitation à diriger des recherches, Université Henri Poincaré - Nancy I, 2005. http://tel.archives-ouvertes.fr/hal-00113500.
Dupont, Maxime. "Dynamics and disorder in quantum antiferromagnets". Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30092/document.
Condensed matter physics, and especially strongly correlated systems provide some of the most challenging problems of modern physics. In these systems, the many-body interactions and correlations between quantum particles cannot be neglected; otherwise, the models would simply fail to capture the relevant physics at play and phenomena ensuing. In particular, the work presented in this manuscript deals with quantum magnetism and addresses several distinct questions through computational approaches and state-of-the-art numerical methods. The interplay between disorder (i.e. impurities) and interactions is studied regarding a specific magnetic compound, where instead of the expected many-body localized phase at high magnetic fields, a novel disorder-induced ordered state of matter is found, with a resurgence of quantum coherence. Furthermore, the dynamical response of quantum magnets to an external perturbation, such as it is accessed and measured in nuclear magnetic resonance and inelastic neutron scattering experiments is investigated
Ludwig, Thomas [Verfasser]. "Interaction and phase relaxation in disordered nanowires and quantum hall systems / Forschungszentrum Karlsruhe GmbH, Karlsruhe. Thomas Ludwig". Karlsruhe : FZKA, 2006. http://d-nb.info/980147859/34.
Stellin, Filippo. "Anderson localization in interacting quantum systems". Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7004.
In this thesis we theoretically investigate the behaviour of quantum particles (electrons, atoms, photons, etc.) moving in a random medium and undergoing Anderson localization. For noninteractingparticles, the energy spectrum can possess one or more critical points, where the nature of the single-particle wavefunctions changes from extended to localized leading to a undergoes a metal-insulator phase transition, also known as Anderson transition.A fundamental question is whether and how Anderson transitions survive in interacting quantum systems. Here we study a minimal model of two particles moving in a disordered lattice and subject to short-range mutual interactions. By combining large-scale numerics with Green’s functions techniques, we show that two-particle Anderson transitions do occur in three dimensions and explore the phase diagram in the space of energy, disorder and interaction strength. The latter presents a rich structure, characterized by a doubly reentrant behavior, caused by the competition between scattering and bound states of the pair. We also show that previous claims of 2D Anderson transitions of the pair are essentially due to finite-size effects.A second problem that we address in this thesis is the occurrence of 2D metal-insulator transitions for a single particle in the presence of a spatially correlated potential and subject to spin-orbit interactions, described by Rashba-Dresselhaus couplings. We illustrate that, irrespective of the properties of the disorder, there is a regime where the critical energy depends linearly on the disorder strength. The slope and the intercept are studied in the vicinity of the spin-helix point, where the SU(2) symmetry is restored and the 2D metal-insulator transition disappears
De, Tomasi Giuseppe [Verfasser], Markus [Gutachter] Heyl, Roland [Gutachter] Ketzmerick, Roderich [Gutachter] Moessner e Frank [Gutachter] Pollmann. "Characterization of ergodicity breaking in disordered quantum systems / Giuseppe De Tomasi ; Gutachter: Markus Heyl, Roland Ketzmerick, Roderich Moessner, Frank Pollmann". Dresden : Technische Universität Dresden, 2018. http://d-nb.info/1226813801/34.
Schneider, Michael Peter [Verfasser], Kurt [Akademischer Betreuer] Busch, Alejandro [Akademischer Betreuer] Saenz e Alexander [Akademischer Betreuer] Shnirman. "A theoretical framework for waveguide quantum electrodynamics and its application in disordered systems / Michael Peter Schneider. Gutachter: Kurt Busch ; Alejandro Saenz ; Alexander Shnirman". Berlin : Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://d-nb.info/1081715995/34.
Meier, Hannes. "Phase transitions in novel superfluids and systems with correlated disorder". Doctoral thesis, KTH, Statistisk fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160929.
QC 20150306
Bourlet, Nicolas. "Dissipative phase transition and duality of the Josephson junction Absence of a dissipative quantum phase transition in Josephson junctions Microscopic charged fuctuators as a limit to the coherence of disordered superconductor devices". Thesis, université Paris-Saclay, 2020. https://tel.archives-ouvertes.fr/tel-03180143.
More than a century after its discovery, superconductivity is used today in many applications. One of those is in superconducting electronics, of which the Josephson junction is a basic building block. This element has enabled the realisation of electronic circuits in the quantum regime, and it has helped redefining the Volt in the SI system around quantum effects. Nowadays, a lot of time and efforts are spent in order to improve Josephson junction based circuits to realise state of the art Quantum-bits for quantum computing. One may think that those highly sensitive experiments involving Josephson junctions and conventional superconductivity imply an exquisite understanding of the component and its behaviour. We show in this thesis work that this is not entirely the case, and we explore two types of superconducting quantum circuits that are in need of clarification. The first one concerns the Josephson junction itself, and a subtle issue regarding its interaction with its electromagnetic environment. Indeed, it has been predicted nearly 40 years ago that a Josephson junction would become insulating when connected to a resistance larger than Rq=h/4e²≈6.45 kΩ. We find no traces of such insulating state in our experiments which measure the admittance of a Josephson junction connected in parallel to a resistance R>Rq. The second circuit we explore is the supposedly dual circuit to the Josephson junction, the quantum phase slip junction, which consists of a nanowire made of a highly inductive superconductor. In those nanowires 2π phase slips of the superconducting phase should produce the dual effects of the Cooper-pair tunneling in Josephson junctions. The control of such an effect would then permit the realisation of a new class of superconducting quantum devices. We measured microwaves resonators patterned in a thin film of a highly inductive superconductor. We find no clear signal revealing the presence of quantum phase slips in our devices. However, we find a clear signature of two-level system low frequency noise, and we explore its implication in this kind of devices
Vieira, Andre de Pinho. "Efeitos de desordem ou aperiodicidade sobre o comportamento de sistemas magnéticos". Universidade de São Paulo, 2002. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-23022012-155648/.
We consider effects of disorder or aperiodicity on three different magnetic systems. First, we present a phenomenological model to describe the thermal dependence of the dilution-induced remanent magnetization in a class of quasi-one-dimensional antiferromagnets. The model treats correlations along the dominant direction in an exact way, while including the remaining inte-. i ractions via an effective field. Then, we use a self-consistent Bethe-Peierls ~ j .. approximation to gauge the effects of a random crystal field on the phase diagram of a mixed-spin Ising mode!. We show that disorder may have profound effects on the multicritical behavior associated with the uniform limit of the mo de!. Finally, we study effects of random or aperiodic interactions on the behavior of the quantum XX chain at low temperatures, by performing numerical calculations based on a mapping of the system onto a free-fermion mo de!. . We present evidence that, at zero temperature, there exists a single, universal fixed-point, associated with a random-singlet phase, which governs the behavior of the model in the presence of disordered interactions. In the case of aperiodic interactions, our results are consistent with renormalizationgroup predictions, indicating, for a certain class of substitution sequences, a behavior similar to the one induced by disorder.
Ossipov, Alexandre. "Open Mesoscopic Systems: beyond the Random Matrix Theory". Doctoral thesis, [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969598173.
Weiss, Markus. "Quantum Hall effect in a strongly disordered system". [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=97263083X.
Voliotis, Dimitrios. "Contribution à l’étude des chaînes de spin quantique avec une perturbation aléatoire ou apériodique". Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0253/document.
In the present thesis, the critical and off-critical behaviors of quantum spin chains in presence of a random or an aperiodic perturbation of the couplings is studied. The critical behavior of the Ising and Potts random quantum chains is known to be governed by the same Infinite-Disorder Fixed Point. We have implemented a numerical version of the Strong-Disorder Renormalization Group (SDRG) to test this prediction. We then studied the quantum random Ashkin-Teller chain by Density Matrix Renormalization Group. The phase diagram, previously obtained by SDRG, is confirmed by estimating the location of the peaks of the integrated autocorrelation times of both the spin-spin and polarization-polarization autocorrelation functions and of the disorder fluctuations of magnetization and polarization. Finally, the existence of a double-Griffiths phase is shown by a detailed study of the decay of the off-critical autocorrelation functions. As expected, a divergence of the dynamical exponent is observed along the two transition lines. In the aperiodic case, we studied both the Ising and Potts quantum chains. Using numerical SDRG, we confirmed the known analytical results for the Ising chains and proposed a new estimate of the magnetic scaling dimension.For the quantum q-state Potts chain, we estimated the magnetic scaling dimension for various aperiodic sequences and showed that it is independent of q for all sequences with a vanishing wandering exponent. However, we observed that the dynamical exponent is finite and increases with the number of states q. In contrast, for the Rudin-Shapiro sequence, the results are compatible with an Infinite-Disorder Fixed Point with a diverging dynamical exponent, equipe de renormalization
Denis, Maxime. "Construction d'une expérience de Condensat de Bose-Einstein de 41K pour l'étude du rotateur frappé atomique". Electronic Thesis or Diss., Université de Lille (2022-....), 2022. http://www.theses.fr/2022ULILR064.
This manuscript presents the realization of an experimental device to produce Bose-Einstein condensates of potassium 41. This experiment was built to study the model of the kicked rotor in the presence of interactions. The choice of potassium 41 for this experiment is motivated by two reasons. The first is that the diffusion length of this atom is positive (allowing easy condensation) and has accessible Feshbach resonances. The second is that the wavelengths of its cooling transitions can be generated by powerful fiber laser sources in the telecom domain doubled in frequency. This has the advantage of being able to manufacture stable and robust laser systems for laser cooling and optical trapping of potassium 41. The particularity of our system lies in the frequency generation that takes place before the high power amplification and frequency doubling stages. The development of these laser benches acting on the two cooling transitions D1 and D2 enabled the laser cooling stages to be completed. Thanks to these laser benches, a magneto-optical trap gathering 3x10^(9) atoms was obtained. Compression and cooling with grey molasses of this magneto-optical trap allowed to reach a temperature of 16 µK and a density in the space of phases of 10^(-6). The following evaporative cooling steps are carried out successively with a quadrupolar trap, a hybrid trap (quadrupolar trap + optical trap) and to finish a crossed optical dipole trap. Condensates of 500,000 atoms were observed in this crossed optical dipole trap. We also identified Feshbach resonances that will allow the control of interactions. For the study of the kicked rotor, an original pulsed laser system was designed in parallel. The realization of this system was made from a high-power amplified telecom pulsed laser doubled in frequency. This system produces near infrared pulses at a repetition frequency between 100 kHz to 500 kHz with peak optical power up to 350W. This pulsed laser bench allowed us to perform the first experiments of the kicked rotor from this experiment. A control of the interactions with the identified Feshbach resonances will allow us to study the model of the kicked rotor in the presence of interactions
Jia, Xun. "A study of disorder effects in quantum systems". Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1905664041&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
Gawiec, Pierre. "Propriétés statiques et dynamiques des états de basse énergie d'un système de spins bidimensionnel anisotrope désordonné". Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10206.
Bishop, Michael Anthony. "Quantum Systems in Bernoulli Potentials". Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/293431.
Fischer, Andrea M. "Disorder and interactions in graphene and other quantum systems". Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/35238/.
Izyumov, Arkady Vasilyevich. "Disorder in quantum and classical systems : field theoretic approach". Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624562.
Thomson, Steven. "The effects of disorder in strongly interacting quantum systems". Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/9441.
Sakaida, Masaru. "Disorder-induced quantum phenomena in inhomogeneous optical lattices". 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215289.
Paulin, Guillaume. "Transport électronique et Verres de Spins". Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2010. http://tel.archives-ouvertes.fr/tel-00556836.
Burdin, Sébastien. "Théories de champ moyen pour les systèmes d'électrons à fortes corrélations". Habilitation à diriger des recherches, Université Sciences et Technologies - Bordeaux I, 2012. http://tel.archives-ouvertes.fr/tel-00711167.
Coquand, Olivier. "Fluctuations dans la phase plate des membranes cristallines". Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS096.
This works deals with the mechanical properties of crystalline membranes, which are two-dimensional materials with an underlying periodic lattice at the microscopic scale which provides them with elastic properties. It is one of the scarce examples of two-dimensional systems possessing a stable ordered phase at large distance in the presence of thermal fluctuations. In that phase, the vectors normal to the surface generated by the membrane are strongly correlated; it is thus called the flat phase. This manuscript presents a study of the properties of the flat phase with help of renormalisation group tools, and in particular the effective average action formalism. First, by studying the perturbation theory beyond lowest order, we confirm the stability of our effective average action ansatz used in the following, and unveil some pathologies of the perturbative development. Then we show how the non-perturbative renormalisation group flow can be used to compute various thermodynamic properties of crystalline membranes and draw their complete phase diagram in the space (volume, applied stress, temperature). Afterwards, we improve our model to account for the effect of quantum fluctuations, which allows to describe the low temperature regime. Finally, we examine the consequences of the presence of various defects in the material. In particular, we describe a new disorder driven phase transition which seems to be in good qualitative agreement with experimental observations
Schiulaz, Mauro. "Ideal quantum glass transitions: many-body localization without quenched disorder?" Doctoral thesis, SISSA, 2015. http://hdl.handle.net/20.500.11767/4908.
Herazo, Warnes Jesus Maria 1982. "Transições de fases quânticas em sistemas bosônicos fortemente correlacionados". [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277709.
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física "Gleb Wataghin"
Made available in DSpace on 2018-09-24T13:52:11Z (GMT). No. of bitstreams: 1 HerazoWarnes_JesusMaria_D.pdf: 4836710 bytes, checksum: 5b7290f1db20bc31b153f3e7202fff39 (MD5) Previous issue date: 2011
Resumo: A questão da natureza das transições de fases de sistemas de redes de bósons tem se tornado cada vez mais urgente à vista da capacidade de carregamento de átomos ultrafrios em redes ópticas. Nesta tese, tentamos avançar este conhecimento através do estudo de 3 modelos básicos de redes de bósons interagentes. Inicialmente, determinamos o diagrama de fases c as propriedades físicas do modelo bosônico de impureza única de Anderson. Este modelo é interessante tanto em si mesmo quanto por causa de sua relação com outras abordagens teóricas tais como a teoria dinâmica de campo médio bosônica. Usamos como estratégia a inclusão de um pequeno campo externo acoplado ao parâmetro de ordem superfluido, que quebra a simetria global de calibre do modelo. Desta forma, foi possível estudar a transição de condensação de Base-Einstein através do critério de quebra espontânea de simetria global de calibre. Outras quantidades como a ocupação da impureza, o desvio padrão da ocupação e a susceptibilidade com respeito ao campo externo também foram calculadas, caracterizando a transição de fase do modelo. Alguns desses resultados foram comparados com aqueles já obtidos na literatura através do grupo de renormalização numérico. Encontramos bom acordo entre os dois métodos. O segundo estudo realizado nesta tese refere-se ao comportamento crítico do modelo de Bose-Hubbard desordenado através da chamada teoria de campo médio estocástica. O objeto central dessa teoria de campo médio é a distribuição de parâmetros de ordem P(?). Estudos numéricos estabelecem que perto da linha crítica que separa as fases superfluida e vidro de Base do modelo, essa distribuição exibe uma grande região com comportamento de lei de potência P(?) ~ ? ^-(1+ß_c), onde ß_c < 1. Usando esse comportamento como tentativa, obtivemos analiticamente tanto a fronteira de fases quanto o valor do expoente crítico da lei de potência ß_c , encontrando um razoável acordo com os resultados numéricos e avançando o entendimento da natureza da transição de fase específica ao modelo desordenado. Finalmente, o modelo de Bose-Hubbard desordenado para partículas de spin-1 foi estudado dentro da teoria de campo médio estocástica. As distribuições de probabilidade de várias quantidades físicas como o parâmetro de ordem superfluido, o desvio padrão da ocupação por sítio, a fração do condensado, o quadrado do operador de spin, bem como seus valores médios, foram determinados para as três fases do modelo, a saber, o superfluido polar, o isolante de Mott e o vidro de Bose. Uma completa caracterização das propriedades físicas dessas fases e das transições de fase entre elas foi estabelecida
Abstract: The question of the nature of phase transitions of systems of lattice bosons has become increasingly more pressing in view of the capability of loading ultracold atoms in opticallattices. In this thesis we try to advance this understanding through the study of 3 basic models of interacting lattice bosons. Initially, we determined the phase diagram and physical properties of the bosonic singleimpurity Anderson model. This model is interesting both in its own right and because of its relation to other theoretical approaches such as the bosonic dynamical field theory method. We used as strategy the inclusion of a small external field coupled to the superfluid order parameter, which breaks the global gauge symmetry of the model. Thus, it was possible to study the Base-Einstein condensation transition through the criterion of the onset of spontaneous broken global gauge symmetry. Other quantities such as the occupation of the impurity, the standard deviation of the occupation and the susceptibility with respect to the external! Field were calculated characterizing the phase transition in the model. Some of the results were compared with those already reported in the literature, obtained with tic numerical renormalization group. We found good agreement between the two methods. The second study carried out in this thesis concerned the critical behavior of the disordered Bose-Hubbard model within the so-called stochastic mean-field theory. The central object of this mean-field theory is the distribution of order parameters P(?). Numerical studies establish that near the critical line separating the superfluid and Bose glass phases of this model, this distribution shows a wide region of power-law behavior P(?) ~ ? ^-(1+ß_c), where ß_c < 1. Using this behavior as an Ansatz, we obtained analytically both the phase boundary and the value of the critical power-law exponent ß_c, finding a reasonably good agreement with the numerical results and thus shedding new light on the nature of this phase transition specific to disordered model. Finally, the disordered Bose-Hubbard model for spin-1 particles was studied within the stochastic mean-field theory. The probability distributions of various physical quantities, such as the superfluid order parameter, the standard deviation of the occupation per site, the condensate fraction, the square of the spin operator, as well as their average values, were determined for the three phases of the model, namely, the polar superfluid, the Mott insulating and the Bose glass phases. A complete characterization of the physical properties of these phases and the phase transitions between them was then established
Doutorado
Física da Matéria Condensada
Doutor em Ciências
Kainaris, Nikolaos [Verfasser], e A. D. [Akademischer Betreuer] Mirlin. "Topology, interactions, and disorder in one-dimensional quantum systems / Nikolaos Kainaris ; Betreuer: A. D. Mirlin". Karlsruhe : KIT-Bibliothek, 2016. http://d-nb.info/1124068864/34.
Wang, Ruizhe. "Magnetic fluctuations and clusters in the itinerant ferromagnet Ni-V close to a disordered quantum critical point". Kent State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=kent1555936445433091.
Sciolla, Bruno. "Dynamique quantique hors-équilibre et systèmes désordonnés pour des atomes ultrafroids bosoniques". Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00734641.
Capron, Thibaut. "Transport quantique dans les verres de spin". Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00686330.
Ruess, Frank Joachim Physics Faculty of Science UNSW. "Atomically controlled device fabrication using STM". Awarded by:University of New South Wales. Physics, 2006. http://handle.unsw.edu.au/1959.4/24855.
Vermersch, Benoît. "Dynamique d'un gaz de bosons ultra-froids dans un milieu désordonné : Effets des interactions sur la localisation et sur la transition d'Anderson". Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2013. http://tel.archives-ouvertes.fr/tel-00910405.
Percebois, Gaëtan. "Quantum transport in two-dimensional systems : artificial intelligence applied to material science". Electronic Thesis or Diss., Strasbourg, 2023. http://www.theses.fr/2023STRAE033.
Heterostructures represent one of the most widely employed devices for generating a two-dimensional electron gas (2DEG). However, the precise transport properties of electrons within such devices remain neither completely controllable nor predictable. This is mainly due to the presence of randomly located ionized dopants, that are necessary for creating the electron gas. However, due to the Coulombic interactions, the electron motion is impacted, which results in a disorder potential. In this study, we introduce a method to determine this disorder potential using local transport information obtained from scanning gate microscopy (SGM) experiments. The mapping between the data captured in an SGM image and the disorder potential is achieved through the utilization of a deep learning algorithm. We have demonstrated that this inverse problem can be solved, and we have been able to determine the disorder potential within a real experimental heterostructure. In this manuscript, we detail the employed methodology, making it replicable for other devices
Petersen, Greg M. "Anderson Localization in Low-Dimensional Systems with Long-Range Correlated Disorder". Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1365762218.
Adroguer, Pierre. "Propriétés de transport électronique des isolants topologiques". Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2013. http://tel.archives-ouvertes.fr/tel-00832048.
Anfray, Valentin. "Étude numérique du point critique de systèmes quantiques de spin désordonnés en dimensions élevées". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0127.
Several random quantum spin models have been numerically studied in dimension D>1 by Strong Disorder Renormalisation Group (SDRG). We have implemented an efficient algorithm to be able to consider a system with up to a billion spins independently of its spatial dimension. Critical properties of the 2D and 3D random quantum Potts model with q=2,3,5,10,20 and 50 states are shown to be governed by an infinite disorder fixed point. We have computed the correlation-length exponent u, the magnetization exponent d_f and the energy gap exponent psi. Using finite-size scaling and taking into account finite-size corrections, critical properties of the Potts model are shown to be q-independent. Random quantum Clock models with q=2,3,5,8 and 10 states have been also studied in 2D and 3D. A minimum amount of initial disorder strength is required to flow to an infinite disorder fixed point. Despite large error bars on psi exponent, our estimates for the critical exponents u and psi for all q are compatible with those of the random transverse-field Ising model. Our estimates for the critical exponent d_f are incompatible within error bar but very close. Lastly, the tricritical point of the random quantum Ashkin-Teller model has been studied in dimension two and three. We have shown that the correlation-length exponent associated with one of the two unstable directions does not belong to the university class of the random transverse-field Ising model
Pereira, Ana Luiza Cardoso 1976. "Destino dos estados estendidos e origem dos estados localizados no regime Hall quântico". [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277032.
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-08-06T19:00:22Z (GMT). No. of bitstreams: 1 Pereira_AnaLuizaCardoso_D.pdf: 2880300 bytes, checksum: ffd133973b4bc6e23c91694bc47d8794 (MD5) Previous issue date: 2005
Resumo: Esse trabalho é dedicado ao estudo de dois problemas de interesse atual em sistemas quânticos de baixa dimensionalidade. Ambos são relacionados ao processo de localização eletrônica no regime Hall quântico. O primeiro problema diz respeito ao destino dos estados estendidos no limite de baixos campos magnéticos ou forte desordem, onde ocorre a transição de líquido de Hall para o isolante de Hall. O problema é abordado através de simulações numéricas, com um modelo de rede bidimensional tratado por um Hamiltoniano tight-binding, considerando-se tanto desordem tipo ruído branco quanto desordem correlacionada com perfil Gaussiano. Nós observamos que à medida que o campo magnético tende a zero ou a desordem é suficientemente aumentada no sistema, os estados estendidos sofrem um deslocamento em relação ao centro das bandas de Landau, indo em direção às mais altas energias e, eventualmente, ultrapassando a energia de Fermi. Esse mecanismo é chamado na literatura de levitação de estados estendidos. Nossos resultados permitem uma análise quantitativa. Identificamos os seguintes parâmetros como sendo os relevantes para mapear a levitação: (i) a razão entre escalas de energia ¿ entre a energia de separação dos níveis de Landau e o alargamento do nível devido à desordem; e (ii) a razão entre escalas de comprimento ¿ entre o comprimento magnético e o comprimento de correlação da desordem. Analisando uma vasta gama de parâmetros, uma expressão de escala descrevendo a levitação de estados estendidos é estabelecida neste trabalho. O segundo problema abordado nesta tese é relacionado ao processo de blindagem do potencial de desordem e ao mecanismo de formação dos estados localizados em sistemas Hall quânticos. O trabalho analítico apresentado aqui é motivado por recentes resultados experimentais, que mostram imagens de microscopia com medidas locais do potencial eletrostático e da compressibilidade desses sistemas, evidenciando como se dá o processo de carga de estados localizados por cargas inteiras ou fracionárias (quase-partículas). Em um regime onde o comportamento é dominado por interações Coulombianas, estabelecemos um modelo eletrostático que descreve o estado localizado como sendo uma região compressível (quantum dot ou antidot) envolta por um plano incompressível, usando a aproximação de Thomas-Fermi para tratar as interações. O potencial eletrostático nas vizinhanças da região compressível é calculado, fornecendo o tamanho dos saltos que ocorrem no potencial à medida que cada carga é adicionada ou removida do estado localizado. Além de mostrar como estes saltos se tornam menores com o aumento do índice de Landau, nossos resultados mostram a dependência deles com a altura de observação do potencial (ou seja, a altura da ponta de prova em relação ao gás de elétrons). O modelo apresentado pode ser usado para tratar estados localizados observados nos platôs do efeito Hall quântico inteiro ou fracionário
Abstract: This work is devoted to the study of two problems of current interest in low dimensional quantum systems. Both are related to the process of electron localization in the quantum Hall regime. The first problem refers to the fate of extended states in the limit of low magnetic fields or strong disorder, where the transition from quantum Hall liquid to Hall insulator takes place. A numerical approach to the problem is used, with a 2D lattice model treated in a tight-binding framework, considering both white-noise and Gaussian correlated disorder. We observe that as the magnetic field vanishes or the disorder is sufficiently increased in the system, the extended states are shifted from the Landau band centers, going to higher energies and, eventually, rising above the Fermi energy. This mechanism is referred in the literature as levitation of extended states. Our results allow a quantitative analysis. We identify the following parameters as the relevant ones to map the levitation: (i) the energy scales ratio - between the energy separation of consecutive Landau levels and the level broadening due to disorder; and (ii) the length scales ratio - between the magnetic length and the disorder correlation length. Analyzing a wide range of parameters, a scaling expression describing the levitation of extended states is established. The second problem considered in this thesis is related to the screening of the disorder potential and to the mechanism of formation of localized states in quantum Hall systems. The analytical work we present here is motivated by recent imaging experiments, which probe locally the electrostatic potential and the compressibility of these systems, showing the charging of individual localized states by integer or fractional charges (quasiparticles). For a regime where the behavior is dominated by Coulomb interactions, we set out an electrostatic model describing the localized state as a compressible region (quantum dot or antidot) embebed in an incompressible background, using the Thomas-Fermi approximation to treat the interactions. The electrostatic potential in the vicinity of the compressible region is calculated, providing the size of potential steps as each charge is added or removed from the localized state. Besides from showing how the potential steps get smaller for higher Landau levels, our results show the dependence of these steps with the height of observation (i.e., the distance from the scanning probe to the electron gas). The proposed model can be used to treat localized states observed on integer or fractional quantum Hall plateaus
Doutorado
Física da Matéria Condensada
Doutor em Ciências
Mukhopadhyay, Ranjan. "Quantum phase transitions in disordered Bose systems". Thesis, 1998. https://thesis.library.caltech.edu/463/1/Mukhopadhyay_r_1998.pdf.