Teses / dissertações sobre o tema "Système quantique de spins"
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Forestier, Guillaume. "Transport quantique dans les verres de spins". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY023/document.
Texto completo da fonteThe experiments presented in this thesis associate two fields of condensed matter physic, on the one hand with the spin glass physic and the other hand with the mesoscopic physic. The spin glass state is one of the most emblematic of disordered and frustred system and at low temperature, it is caracterized by an unconventionel order where the magnetic disorder is quenched. Moroever, it is considered as a model system for glasses in general and thereby it has been extensively studied, both experimentally and theoreticlly. After extensive research efforts, the description of fundamental state of the system has lead towards two well different approaches. The first, given by the mean field solution, highlights a fundamental composed of mulitple states organised and hierarchical. The second, called droplet model is based on the off--equilibrium dynamic of a unique ground state. However, despite these contributions, the understanding ot this phase is far from being complete and the nature of the ground state still remains an open question. In a mesoscopic conductor, the transport of electron is coherent: electrons keep the memory of their phase, so that one can observe interference effects. The main motivation of this work is to use these interference effects in order to to probe the spin glass state. Indeed, as electronic interference depends of the position of the static disorder, coherent transport can be a useful tool to study the configuration of the microscopic disorder. Althought few coherent transport experiments exist to probe the spin glass, this field of research has very little explored. Nevertheless, this area has been a revival thanks to theoritical work, showing how coherent transport is sensitived to the quenched disorder and how it may provide informations of the nature of fundamental state of spin glass. So, this experimental work deals with the implementation of transport measurements in mesoscopic spin glasses. The first part of the study is focused on the general charateristics of classical and quatum transport of these system. We have examined the resistivity as a function of the temperature and magnetic field and we show that these mesoscopic systems have a spin glass-like behaviour. In a second part, we have focused on the low field magnetoresistivity. We show that it presents a strong hysteresis, whose the amplitude is strongly depends, both of the temperature in the glassy phase and sweeping rate of the magnetic field. We argue that this particular behaviour is related to the out off-equilibrium of the system and we show how the temperature and the sweeping rate control the deviation to the equilibrium. In this part, we also examine by transport measurements how the system relaxes towards the equilibrium just after its excitation. In addition, we present surprinsing transport propreties that we observed, resulting of experimental protocols more sophisticated in temperatures and magnetic fields
Clémancey, Martin. "Etude RMN du système de spins quantiques CuHpCl". Université Joseph Fourier (Grenoble), 2004. http://www.theses.fr/2004GRE10037.
Texto completo da fonteWe present an NMR study of magnetic properties of Cu2(C5H12N2)2Cl4(CuHpCl). This system of quantum spins 1/2 has been considered for a long time as an experimental realization of a spin ladder system. Its phase diagram under magnetic field is very rich, in particular a spin liquid ground state in zero field and two quantum phase transitions at Hcl=7. 5Tesla and Hc2=13Tesla. The first goal of this study was a clarification of some specific parts of the phase diagram, in particular the low temperature regime beetwen Hcl and Hc2, where tridimensional magnetic order sets in. Trought the study of a compound deuterated on specific hydrogen bonds, we observed the commensurate nature of this ordered phase. The second-order phase transition was studied as a function of H and T. The main result of this study interactions, like observed in other spin liquid componds like NENP or SrCu(Bo3). This "anomalus" staggered magnetisation 3D magnetic order can be observed. We also observed by torque magnetometry anomalous features due to this staggered magnetisation. Last, in order to understand the magnetic exchange pathways in CuHpCl, we also undertook NMR and torque measurements of methylated of CuHpCl
Dimo, Panjio Claude. "Étude des modèles de Richardson-Gaudin de spin-½ avec champ magnétique arbitraire". Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0154.
Texto completo da fonteThis thesis is divided into three parts and extended over seven chapters between the general introduction and conclusion. Indeed, the first part, consisting of four chapters, is mainly focused on a static study of Richardson-Gaudin models of spin 1/2 with arbitrary magnetic field including the possibility of a totally anisotropic XYZ coupling such that the terms "S^x_jS^x_k , S^y_j S^y_k mathrm{and} S^z_j S^z_k" all have distinct coupling strengths. In this part we determine generically the energy spectrum, the central spin mean values, the wave functions and the two-point correlation functions of the considered models; which will be useful for an advanced dynamical analysis of these models. The calculation of the energy spectrum of the current system can exploit its integrability which is materialized by a set of equations constituting the integrability condition. This calculation is done independently of the symmetry of the model considered and involves the resolution of a system of quadratic equations that is relatively simple to solve numerically.The second part focuses on some examples of applications that could be implemented on the basis of the results obtained in part I. Indeed, it has recently been shown that the XX central spin model is integrable. It describes a particular spin coupled via XX spin-spin couplings to a bath of other spins while feeling a magnetic field along the "hat{z}" axis, i.e. perpendicular to the plane in which the coupling exists. What interests us here is first to demonstrate that the XX central spin model remains integrable in the presence of an arbitrarily oriented magnetic field. In a second step we study whether the dark states remain in this case. The U(1) symmetry of the considered model is broken by the addition of an external field component in the XY plane, which could lead to a radically different physics. Nevertheless, we show that, for a sufficiently strong coupling, the structure of the dark states reappears even in the presence of a magnetic field in the plane. A simple understanding of this result and the demonstration of the universality of the results by a finite size scale study and for a variety of distinct distributions of the coupling constants at the different spins of the bath. Another example of application which closes this second part is that of the XXX dark states with arbitrary magnetic field. These states, although having a different physics from the one encountered in the previously studied models, exist and a generic law has been established to count them.This law has been verified up to 12 spins in the bath, so we can assume that it also works beyond 12 spins in the bath, we can conjecture that it is valid for any value of N.The third part of this project is dedicated to a dynamic study of non-integrable models similar to those studied in the first part of this manuscript. Indeed, these models are just the representation of Richardson-Gaudin models immersed in a time dependent magnetic field oriented along "hat{z}".In a process of rotation around the "hat{z}" axis of the magnetic field associated to the central spin, it is possible to define a time dependent basis in which the time dependent problem reduces to an independent problem. The resulting Hamiltonian can then be integrable and require the use of the results found in the first part to be solved. For these models, by imagining for example that the system is initially prepared in a dark state of the static Hamiltonian, we clearly see that its dynamics is not trivial and leads to perfect oscillations of this state.Finite size systems resulting from the central spin models treated in this thesis depend strongly on the distribution of couplings between the central spin and each nuclear spin constituting the bath
Platini, Thierry. "Chaînes de spins quantiques hors de l'équilibre". Phd thesis, Université Henri Poincaré - Nancy I, 2008. http://tel.archives-ouvertes.fr/tel-00439896.
Texto completo da fonteAtas, Yasar Yilmaz. "Quelques aspects du chaos quantique dans les systèmes de N-corps en interaction : chaînes de spins quantiques et matrices aléatoires". Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112221/document.
Texto completo da fonteMy thesis is devoted to the study of some aspects of many body quantum interacting systems. In particular we focus on quantum spin chains. I have studied several aspects of quantum spin chains, from both numerical and analytical perspectives. I addressed especially questions related to the structure of eigenfunctions, the level densities and the spectral properties of spin chain Hamiltonians. In this thesis, I first present the basic numerical techniques used for the computation of eigenvalues and eigenvectors of spin chain Hamiltonians. Level densities of quantum models are important and simple quantities that allow to characterize spectral properties of systems with large number of degrees of freedom. It is well known that the level densities of most integrable models tend to the Gaussian in the thermodynamic limit. However, it appears that in certain limits of coupling of the spin chain to the magnetic field and for finite number of spins on the chain, one observes peaks in the level density. I will show that the knowledge of the first two moments of the Hamiltonian in the degenerate subspace associated with each peak give a good approximation to the level density. Next, I study the statistical properties of the eigenvalues of spin chain Hamiltonians. One of the main achievements in the study of the spectral statistics of quantum complex systems concerns the universal behaviour of the fluctuation of measure such as the distribution of spacing between two consecutive eigenvalues. These fluctuations are very well described by the theory of random matrices but the comparison with the theoretical prediction generally requires a transformation of the spectrum of the Hamiltonian called the unfolding procedure. For many-body quantum systems, the size of the Hilbert space generally grows exponentially with the number of particles leading to a lack of data to make a proper statistical study. These constraints have led to the introduction of a new measure free of the unfolding procedure and based on the ratio of consecutive level spacings rather than the spacings themselves. This measure is independant of the local level density. By following the Wigner surmise for the computation of the level spacing distribution, I obtained approximation for the distribution of the ratio of consecutive level spacings by analyzing random 3x3 matrices for the three canonical ensembles. The prediction are compared with numerical results showing excellent agreement. Finally, I investigate eigenfunction statistics of some canonical spin-chain Hamiltonians. Eigenfunctions together with the energy spectrum are the fundamental objects of quantum systems: their structure is quite complicated and not well understood. Due to the exponential growth of the size of the Hilbert space, the study of eigenfunctions is a very difficult task from both analytical and numerical points of view. I demonstrate that the groundstate eigenfunctions of all canonical models of spin chain are multifractal, by computing numerically the Rényi entropy and extrapolating it to obtain the multifractal dimensions
Dillenschneider, Raoul. "Effects of a strict site-occupation constraint in the description of quantum spin systems at finite temperature". Université Louis Pasteur (Strasbourg) (1971-2008), 2006. https://publication-theses.unistra.fr/public/theses_doctorat/2006/DILLENSCHNEIDER_Raoul_2006.pdf.
Texto completo da fonteWendenbaum, Pierre. "Intrication et dynamique de trempe dans les chaînes de spins quantiques". Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0170/document.
Texto completo da fonteThe study carried in this thesis concerns the dynamics of out-Of-Equilibrium quantum systems, and more particularly their entanglement properties. Indeed, entanglement became a fundamental concept in modern physics, especially with the development of quantum information. We have in a first part studied the dynamics of a model of bosons on a lattice after the quench of their trapping potential. In the hard-Core limit, we developed an hydrodynamical theory which perfectly reproduced the observed behavior. Then, we have looked at the dynamics of two defect spins coupled to an Ising chain. When these defects have been prepared into a separable state, we have established a formula giving the evolution of the reduced density matrix, allowing us to have access to the entanglement create through the coupling to the chain. We considered then the case of two initially entangled defect spins, and we studied the influence of a non-Equilibrium environment on the disentanglement properties. Finally, the last part of this thesis is devoted to the study of a system coupled to an environment by means of the repeated interactions process. We studied the relaxation of the system in two different time regimes. For short times, the state is well described by a non-Equilibrium-Steady-State, in which we highlighted the scaling properties of some observables. For long times, the system reaches an equilibrium steady state made of a product of Bell states
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.
Texto completo da fonteSeveral 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
Bocquet, Marc. "Chaînes de Spins, Fermions de Dirac, et Systèmes Désordonnés". Phd thesis, Ecole Polytechnique X, 2000. http://tel.archives-ouvertes.fr/tel-00001560.
Texto completo da fonteCapron, Thibaut. "Transport quantique dans les verres de spin". Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00686330.
Texto completo da fonteGawiec, 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.
Texto completo da fonteZhou, Jiaqi. "Etude ab initio du transport quantique dépendant du spin". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS508/document.
Texto completo da fonteSpintronics devices manipulate the electron spin degree of freedom to process information. In this thesis, we investigate spin-dependent quantum transport properties to optimize the performances of spintronics devices. Through ab initio approach, we research the tunneling magnetoresistance (TMR), spin Hall effect (SHE), as well as spin injection efficiency (SIE). It has been demonstrated that heavy metals (HMs) are able to modulate TMR effects in MgO-based magnetic tunnel junctions (MTJs), and tungsten, molybdenum, and iridium are promising to enhance TMR. Moreover, substitutional atom doping can effectively optimize SHE of HMs, which would strengthen spin Hall angles (SHAs) to achieve efficient spin-orbit torque (SOT) switching of MTJs. To eliminate the mismatch between ferromagnetic and barrier layers in MgO-based MTJs, we design the MTJ with bond-free van der Waals (vdW) heterojunction VSe₂/MoS₂ and report the room-temperature TMR. The occurrence of quantum-well resonances enables voltage control to be an effective method to modulate TMR ratios in vdW MTJ. We put forward the idea of SOT vdW MTJ, which employs SOT to switch vdW MTJ and requires vdW materials with strong SHE. Research on MoTe₂ and WTe₂ verifies the possibility of realizing this idea. Both of them are layered transition metal dichalcogenides (TMDC) and exhibit strong SHEs, as well as large SHAs thanks to their low electrical conductivity. Lastly, motivated by the demand of a two-dimensional (2D) switchable device with long spin diffusion length, we construct the spin injection system with silicene monolayer, and reveal high SIEs under electric fields. Works in this thesis would advance the research of spintronics devices
Domenge, Jean-Christophe. "Brisures de symétrie dans les modèles de Heisenberg classiques et quantiques en deux dimensions". Paris 6, 2005. https://tel.archives-ouvertes.fr/tel-00010943.
Texto completo da fonteGrezes, Cécile. "Towards a spin ensemble quantum memory for superconducting qubits". Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066635.
Texto completo da fonteThis thesis work discusses the development of a hybrid quantum processor, in which collective degrees of freedom of an ensemble of spins are used as a multimode quantum memory for superconducting qubits. We design a memory protocol able to store and retrieve on demand the state of a large number of qubits in a spin ensemble and we demonstrate building blocks of its operations with NV centers in diamond. The protocol relies on the coupling of the NV ensemble to a resonator with tunable frequency and quality factor. Incoming quantum states are written by resonant absorption of a microwave photon in the spin ensemble, and then read out of the memory by applying a sequence of control pulses to the spins and to the resonator. The write step of the protocol is demonstrated in a first experiment by integrating on the same chip a superconducting qubit, a resonator with tunable frequency, and the NV ensemble. Arbitrary qubit states are stored into the spin ensemble via the resonator. After storage, the resulting collective quantum state is rapidly dephased due to inhomogeneous broadening of the ensemble and a refocusing sequence must be applied on the spins to bring them to return in phase and to re-emit collectively the quantum state initially absorbed as an echo. In a second experiment, we demonstrate an important building block of this read-out operation, which consists in retrieving multiple classical microwave pulses down to the single photon level using Hahn echo refocusing techniques. Finally, optical repumping of the spin ensemble is implemented in order to reset the memory in-between two successive sequences
Gauthé, Olivier. "Méthodes de réseaux de tenseurs pour les systèmes de spins SU(N)". Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30279.
Texto completo da fonteThe study of strongly correlated electron systems is one of the most challenging target of modern condensed matter physics. Beyond the Mott transition, these systems are magnetic insulators that can be described by a spin wavefunction. This concept can be generalized by replacing the spin variable by an irreducible representation of the group SU(N), which is relevant in some cold atomic gases experiments. This thesis aims to determine the physical properties of paradigmatic wavefunctions of condensed matter systems ruled by SU(N) symmetry using tensor network algorithms. These methods have already proven to be efficient to tackle problems with discrete variables on a lattice. Here, the formalism of Projected Entangled Pair States (PEPS) is used to design elementary tensors with intrinsic SU(N) symmetry that describe quantum spin liquid phases. This method is first applied to the generalization to SU(3) symmetry group and in two dimensions on the square lattice of the Affleck-Kennedy-Lieb-Tasaki (AKLT) wavefunction. It is shown to belong to the class of symmetry protected topological phases. Subsequently, the generalization to SU(N) of resonant valence bond (RVB)-like states on the square lattice is investigated, first for staggered fundamental-conjugate representations. A system of two SU(4) fermions per site is then considered and described with generalized RVB wavefunctions. These states are shown to represent a Z2 topological quantum spin liquid, possibly chiral, that does not break any spatial symmetry. A reasonable, short-range Hamiltonian able to stabilize this phase is proposed
Stephan, Jean-Marie. "Intrication dans des systèmes quantiques à basse dimension". Thesis, Paris 11, 2011. http://www.theses.fr/2011PA112308.
Texto completo da fonteIn recent years, it has been understood that entanglement measures can be useful tools for the understanding and characterization of new and exotic phases of matter, especially when the study of order parameters alone proves insufficient. This thesis is devoted to the study of a few low-dimensional quantum systems where this is the case. Among these measures, the entanglement entropy, defined through a bipartition of the quantum system, has been perhaps one of the most heavily studied, especially in one dimension. Such a quantity is usually very difficult to compute in dimension larger than one, but we show that for a particular class of wave functions, named after Rokhsar and Kivelson, the entanglement entropy of an infinite cylinder cut into two parts simplifies considerably. It can be expressed as the Shannon entropy of the probability distribution resulting from the ground-state wave function of a one-dimensional quantum system. This dimensional reduction allows for a detailed numerical study (free fermion, exact diagonalizations, \ldots) as well as an analytic treatment, using conformal field theory (CFT) techniques. We also argue that this approach can give an easy access to some refined universal features of a given wave function in general.Another part of this thesis deals with the study of local quantum quenches in one-dimensional critical systems. The emphasis is put on the Loschmidt echo, the overlap between the wave function before the quench and the wave function at time t after the quench. Because of the commensurability of the CFT spectrum, the time evolution turns out to be periodic, and can be obtained analytically in various cases. Inspired by these results, we also study the zero-frequency contribution to the Loschmidt echo after such a quench. It can be expressed as a simple overlap -- which we name bipartite fidelity -- and can be studied in its own right. We show that despite its simple definition, it mimics the behavior of the entanglement entropy very well. In particular when the one-dimensional system is critical, this fidelity decays algebraically with the system size, reminiscent of Anderson's celebrated orthogonality catastrophe. The exponent is universal and related to the central charge of the underlying CFT
Camara, Ibrahima Sock. "Étude, par Résonance de Spin Électronique, de la dynamique des spins dans les composés à base de dimères de spins 1/2, CsV2O5, VO(HPO4)*0.5H2O et KZn(H2O)(VO)2(PO4)2(H2PO4)". Phd thesis, Aix-Marseille Université, 2012. http://tel.archives-ouvertes.fr/tel-00747670.
Texto completo da fonteMessio, Laura. "Etats fondamentaux et excitations de systèmes magnétiques frustrés, du classique au quantique". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2010. http://tel.archives-ouvertes.fr/tel-00523976.
Texto completo da fonteMichéa, Sébastien. "Quelques applications des groupes de Lie de dimension infinie en systèmes de spins et en théorie topologique des champs". Dijon, 1999. http://www.theses.fr/1999DIJOS002.
Texto completo da fonteWieland, Wolfgang. "Structure chirale de la gravité quantique à boucles". Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4094/document.
Texto completo da fonteGeneral relativity is the most precise theory of the gravitational interaction. It is a classical field theory. All matter, on the other hand, follows the rules of quantum theory. At the Planck scale, at about distances of the order of 10E-35 meters, both theories become equally important. Today, theoretical physics lacks a unifying language to explore what happens at this scale, but there are several candidate theories available. Loop quantum gravity is one them, and it is the main topic of this thesis. To see whether a particular proposal is a viable candidate for a quantum theory of the gravitational field it must be free of internal inconsistencies, and agree with all experimental tests of general relativity. This thesis develops mathematical tools to check these
Silva, Fernanda Deus da. "Contributions aux propriétés de transport d'un système à N Corps". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GRENY007/document.
Texto completo da fonteWe study some important problems related to the transport properties of many body systems. It is divided in three parts, each one focusing in a specific topic. We obtain relevant results that improve our understanding of these systems. We investigate the effect of dissipation and time-dependent external sources, in the phase diagram of a many body system at zero and finite temperature. In the presence of time-dependent perturbations, dissipation is essential for the system to attain a steady, time independent state. In order to treat this time dependent problem, we use a Keldysh approach within an adiabatic approximation that allows us to study the phase diagram of this system as a function of the parameters of the system and temperature. We also discuss the nature of the quantum phase transitions of the system. Next, we study an important concept in the physics of metallic multi-band systems, that of hybridization, and how it affects the superconducting properties of a material. A constant or symmetric $k$-dependent hybridization in general act in detriment of superconductivity. We show here that when hybridization between orbitals in different sites assumes an anti-symmetric character having odd-parity it {it{enhances}} superconductivity. The antisymmetric hybridization in a problem study in this thesis (present in Chapter 3) allow us to propose a new system where it is possible to investigate Majorana fermions, even in absence of spin-orbit interactions. In the last part of this thesis we study the effect of spin-orbit coupling (SOC) on transport properties in magnetic nanostructures. In this system SOC plays an important role, because surfaces (or interfaces) introduce symmetry breaking which is a source of spin-orbit interaction. We study the role of Dzyaloshinshkii-Moriya (DM) interaction on spin-transport in a 3 layer system. We show that there is a DM interaction between magnetics ions in the layers and spin of conduction electrons. We study the influence of this DM interaction on transport within a simple model where each layer is represented by a point
Laurent, Sabine. "Orientation optique et relaxation du spin du trion dans les boîtes quantiques d'InAs/GaAs". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2004. http://tel.archives-ouvertes.fr/tel-00007028.
Texto completo da fonteSolana, Mathias. "Electronic transport in spin-glasses and mesoscopic wires : correlations of universal conductance fluctuations in disordered conductors". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY020/document.
Texto completo da fonteThe experimental work developed during this PhD is situated at the interface of two fields of condensed matter physics, namely spin glasses and mesoscopic physics. Spin glasses have been widely studied and are one of the problem that has been the most discussed over the years, both on a theoretical and experimental point of view. This state is characterized by very peculiar properties that come to light as it exhibits a magnetic phase transition at low temperatures that is already unusual. Indeed, this transition is due to a mix of frustration and disorder in the magnetic structure of the system, making it an exceptional model system for glasses and frustrated systems in general. After many efforts, theoreticians managed to described the fundamental state of the system by the mean of two different and apparently incompatible approaches. The first one, called RSB theory, is based on a mean-field approximation and predicts a complex phase space with an unconventional hierarchical organization. The second is based on more phenomenological approach and is named Droplet theory. It points towards a unique ground state and explain all the observation by slow relaxation processes. However, the question of the true nature of the spin glass phase is still heavily debated. Mesoscopic physics, for its part, addresses the question of electronic transport for samples in which the electrons keep their phase coherence. If the electrons remains coherent, it is possible to see interference effects that are quantum signs of what happens at the atomic level. In this work, it is used to probe the magnetic and static disorder in spin glasses. Indeed, it is possible to interpret the change in those interferences as changes in the microscopic disorder configuration and to know exactly how the spin glass state evolves. Some work have already tried to use coherent transport in spin glasses but this remains an open field. This work has then be dedicated to the implementation of transport measurement in spin glasses and mesocopic conductors. The first part will be focused on a the experimental setup that was used to perform very precise transport measurements and on the processing of the data taken out of them. In a second part, we will present some general physical characteristics of our samples such as their resistance dependence to the temperature or magnetic field, before extracting the quantum signature in magnetoresistance measurements. Finally, we will discuss the results obtained. We show that strong changes in the microscopic disorder happen even at low temperatures, in opposition to what is believed. We argue that those observed changes are purely structural and come from systems that are widely distributed in energy
Bondesan, Roberto. "Edge states and supersymmetric sigma models". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://tel.archives-ouvertes.fr/tel-00808736.
Texto completo da fonteMöller, Gunnar. "Espaces dynamiques réduits en physique de la matière condensée :Systèmes à effet Hall bicouches, réduction dimensionnelle et systèmes de spins magnétiques". Phd thesis, Université Paris Sud - Paris XI, 2006. http://tel.archives-ouvertes.fr/tel-00121765.
Texto completo da fonteOn introduit une classe générale d'états appariés de fermions composites. Ces fonctions d'onde sont exploitées pour analyser l'état fondamental des systèmes bicouches à effet Hall au facteur de remplissage total un. A partir d'une étude de Monte Carlo variationnel nous concluons que la transition de phase compressible à incompressible observée dans ce système est du deuxième ordre. Nous étudions également la question de l'existence d'un état apparié à demi-remplissage dans les simples couches. Ensuite nous considérons des schémas de réduction dimensionnelle de systèmes bidimensionnels sur la sphère vers des systèmes unidimensionnels sur le cercle. Un tel mapping est établi pour des systèmes libres et un candidat pour un système d'anyons généralisé est proposé. Finalement, nous analysons les systèmes de spins magnétiques sur réseaux bidimensionnels et discutons si un état de glace de spins peut exister en présence d'interactions dipolaires à longue portée.
Brunel, Vivien. "Systèmes de spins quantiques unidimensionnels. Désordre et impuretés". Phd thesis, Université Paris Sud - Paris XI, 1999. http://tel.archives-ouvertes.fr/tel-00000893.
Texto completo da fonteVillar, Vincent. "Etude expérimentale des effets quantiques dans deux systèmes de spins : aimant moléculaire Fe8 et chaîne de spins quantiques". Université Joseph Fourier (Grenoble), 2001. http://www.theses.fr/2001GRE10255.
Texto completo da fonteBRUNEL, VIVIEN. "Systemes de spins quantiques unidimensionnels desordre et impuretes". Paris 11, 1999. http://www.theses.fr/1999PA112142.
Texto completo da fonteMöller, Gunnar. "Dynamically reduced spaces in condensed matter physics : quantum Hall bilayers, dimensional reduction and magnetic spin systems". Paris 11, 2006. http://www.theses.fr/2006PA112131.
Texto completo da fonteFor a description of the low-temperature physics of condensed-matter systems, it is often useful to work within dynamically reduced spaces. This philosophy equally applies to quantum Hall bilayer systems, anyon systems, and frustrated magnetic spin systems - three examples studied in this thesis. First, we developed a new class of wave functions based upon paired composite fermions. These were applied to analyze the physics of the quantum Hall bilayer system at total filling one. Studying these via variational Monte Carlo methods, we concluded that the compressible to incompressible transition in the bilayer system is of second order. Furthermore, we pursued the longstanding question of whether pairing in the single layer might cause an incompressible quantum state at half filling. We then considered schemes of dimensional reduction for quantum mechanical models on the sphere. We achieved a mapping from non-interacting particles on the sphere to free particles on the circle. We proposed that an analogous mapping might exist for interacting anyons, and an appropriate anyon-like model on the sphere was introduced. Lastly, we performed an analysis of magnetic spin systems on two-dimensional lattices addressing the question of whether spin-ice can be realized in the presence of long-range dipolar interactions
Dréau, Anaïs. "Spins individuels dans le diamant pour l'information quantique". Thesis, Cachan, Ecole normale supérieure, 2013. http://www.theses.fr/2013DENS0055/document.
Texto completo da fonteThe principle of quantum information relies on processing information, not from a classical point of view but from a quantum one, in order to increase the efficiency of some computer algorithms. Fulfilling such a goal requires the construction of a quantum register, for instance by coherently putting together a large number of individual quantum systems which play the role of quantum information bits. In this respect, a lot of research has focused on the NV colored center of diamond as it constitutes one of the few systems which can be used as a solid-state quantum bit at room temperature. This doctoral thesis studies the interactions between the NV electronic spin and surrounding nuclear spins located in the diamond matrix, with the intention of creating diamond quantum hybrid systems. We first explain how the NV electronic spin can be used to detect nuclear spins dispersed inside the diamond. Then, we use the NV center as an ancillary quantum bit to initialize the state of these nuclear spins, either by benefitting from a level-anticrossing, or by implementing a projective measurement. Finally, we analyse the origins of the limitation of the coherence time of NV centers in ultrapure diamond samples caused by the interaction with a surrounding nuclear spin bath. Besides their interest for quantum information processing, the study and control of spins in diamond also open the path to making highly sensitive nano-sensors, for which applications can be found in numerous fields of modern physics
Louchet, Anne. "Manipulation optique d'une cohérence de spin nucléaire dans l'ion thulium en matrice cristalline". Phd thesis, Université Paris Sud - Paris XI, 2008. http://tel.archives-ouvertes.fr/tel-00345345.
Texto completo da fonteGranet, Étienne. "Advanced integrability techniques and analysis for quantum spin chains". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS239.
Texto completo da fonteThis thesis mainly deals with integrable quantum critical systems that exhibit peculiar features such as non-unitarity or non-compactness, through the technology of Bethe ansatz. These features arise in non-local statistical physics models such as percolation, but also in disordered systems for example. The manuscript both presents detailed studies of the continuum limit of finite-size lattice integrable models, and develops new techniques to study this correspondence. In a first part we study in great detail the continuum limit of non-unitary (and sometimes non-compact) super spin chains with orthosymplectic symmetry which is shown to be supersphere sigma models, by computing their spectrum from field theory, from the Bethe ansatz, and numerically. The non-unitarity allows for a spontaneous symmetry breaking usually forbidden by the Mermin-Wagner theorem. The fact that they are marginal perturbations of a Logarithmic Conformal Field Theory is particularly investigated. We also establish a precise correspondence between the spectrum and intersecting loops configurations, and derive new critical exponents for fully-packed trails, as well as their multiplicative logarithmic corrections. During this study we developed a new method to compute the excitation spectrum of a critical quantum spin chain from the Bethe ansatz, together with their logarithmic corrections, that is also applicable in presence of so-called ’strings’, and that avoids Wiener-Hopf and Non-Linear Integral Equations. In a second part we address the problem of the behavior of a spin chain in a magnetic field, and show that one can derive convergent series for several physical quantities such as the acquired magnetization or the critical exponents, whose coefficients can be efficiently and explicitely computed recursively using only algebraic manipulations. The structure of the recurrence relations permits to study generically the excitation spectrum content – moreover they are applicable even to some cases where the Bethe roots lie on a curve in the complex plane. It is our hope that the analytic continuation of such series might be helpful the study non-compact spin chains, for which we give some flavour. Besides, we show that the fluctuations within the arctic curve of the six-vertex model with domain-wall boundary conditions are captured by a Gaussian free field with space-dependent coupling constant that can be computed from the free energy of the periodic XXZ spin chain with an imaginary twist and in a magnetic field
Colombier, Estelle. "Développement instrumental pour les mesures de résistivité sous pression hydrostatique. Étude de systèmes à électrons corrélés d'ytterbium et de la famille A0,33V2O5". Phd thesis, Université Joseph Fourier (Grenoble), 2008. http://tel.archives-ouvertes.fr/tel-00305344.
Texto completo da fonteDans ce but, une nouvelle technique de mesure de résistivité sous pression a été mise au point pour appliquer jusqu'à 8 GPa à des échantillons de taille millimétrique.
Nous avons montré qu'aucune phase magnétique n'apparait sous pression au-dessus de 2 K pour le composé YbAl3, jusqu'à 6 GPa.
Des mesures de résistivité sur des monocristaux d'YbCu2Si2 ont mis en évidence une anisotropie. YbCu2Si2, magnétique à partir d'environ 8 GPa, a été mesuré sous pression pour établir un diagramme de phase précis.
Enfin, nous discutons des raisons expérimentales qui nous ont empêché d'observer la supraconductivité dans le composé Na0,33V2O5.
Colombier, Estelle. "Développement instrumental pour les mesures de résistivité sous pression hydrostatique. Étude de systèmes à électrons corrélés d'ytterbium et de la famille A0,33V2O5". Phd thesis, Grenoble 1, 2008. http://www.theses.fr/2008GRE10048.
Texto completo da fonteWe investigate in extreme conditions of high pressure and low temperature the phase diagram (p,T) for ytterbium-based strongly correlated electron compounds, and also the superconducting phase which appears under pressure in the spin-ladder compound Na0,33V2O5. Particular emphasis is made on high quality crystals and good hydrostatic conditions. To achieve this, we developed a new technique to measure resistivity under pressure up to 8 GPa to millimetric samples. We showed that no magnetic phase exists under pressure up to about 6 GPa for YbAl3, down to 2 K. Resistivity measurements on high quality YbCu2Si2 single crystals showed anisotropy. We performed measurements under pressure to investigate precisely the phase diagram in the vicinity of the magnetic phase appearance, around 8 GPa. Resistivity measurements were performed on the spin ladder compound Na0,33V2O5 to 7 GPa. We discuss about experimental reasons which prevent us to observe the superconducting phase
Ferhat, Karim. "Fluctuations quantiques dans des systèmes de spins et de charges en interaction". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY087/document.
Texto completo da fonteThis thesis focuses on two different spin and charge systems, interacting under the effect of quantum fluctuations.The first project highlights the phase diagram of interacting electrons on a kagome lattice. This diagram is driven by two Coulomb repulsions. The first is a on site repulsion, and the second a nearest neighbor one. These two repulsions are in competition with quantum fluctuations of electronic charges. Four phases are depicted, two are unknown and the two other are in agreement with the literature. The two new phases are stabilized in the strong on site repulsion regime. When nearest neighbor repulsions are strong enough to induce a charge local constraint, the system enters in a so called Heisenberg-Loop Phase. These loops are antiferromagnetically arranged and can be described by a Heisenberg-like model in which both charge and spin play surprisingly a role in the exchange interaction. The second new phase is stabilized in the regime where nearest neighbor interactions are too weak to maintain the local constraint. Then, half of the electrons are delocalized in unidimensional Bloch states similar to quantum polarized electronic bubbles. These bubbles are trapped in an inversely polarized electronic cristal formed by the other electrons. This peculiar phase is favored by both quantum charge fluctuations in the bubbles, and antiferromagnetic exchanges between their electrons and the cristal ones.The second project deals with a Terbium Double-Decker molecular magnet. This molecule is modeled by three interacting degrees of freedom. The first is a nuclear spin of the Terbium ion, and the second is the electronic spin of this same ion. The two spins interact via a magnetic exchange.In a first approximation, the effect of the electronic spin is to induce a dipolar field. Finally, the last degree of freedom is carried by two ligands under the influence of the dipolar field. The ligands play the role of a read-out quantum dot, and by conductance measurements through this last one, we can probe the electronic spin and then, the nuclear spin. The first step of this project highlights the modeling of the global system. Then numerical computations are depicted and are in a quantitative agreement with the experimental measurements realized during the thesis of Stefan Thiele and Clément Godfrin.On the other hand, by applying electrical Radio Frequency Fields, we can drive quantum fluctuations on the nuclear spin. This quantum manipulation of the spin is realized by the dynamic deformation of the electron cloud under the effect of the Radio Frequency Field. As a result, we are able to implement a Grover Quantum Algorithm on the nuclear field. This thesis focuses on the realization of a simulation program that was a tool used by Clément Godfrin to successfully implement the Grover Algorithm
Van, Den Berg Tineke. "Conductivité de spin et effets magnétiques dans les systèmes quantiques désordonnés". Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4812/document.
Texto completo da fonteSpintronics is a research area that is concerned with the storage and transfer of information by means of electron spins. In the first part we investigated the intrinsic spin Hall effect in the presence of disordered magnetic impurities in a paramagnetic state in a two dimensional electron gas with Rashba spin-orbit coupling. In the presence of weak magnetic disorder the spin Hall conductivity stays close to its universal (clean system) value, as shown by analytical linear response calculations and numerical simulations. Heavy spin conductivity fluctuations are observed, that increase with disorder strength. To investigate the spreading of a wavepacket on a lattice we measure the wavepacket width, the inverse participation ratio and the (2)-fractal dimension. It is shown the system undergoes a localization transition at a critical disorder strength. In the localized regime the local density of states is not uniform anymore. An anti-ferromagnetic correlation between electron spins and impurity magnetic moments is observed. Beyond the localization transition the spin conductivity increases significantly. The first quantum (Cooperon) corrections in the linear response formalism are shown to contribute positively to the spin Hall conductivity. In the second part the double exchange Hubbard model for correlated electron systems is studied using dynamical mean field theory (DMFT) with the non-crossing approximation (NCA). Around quarter filling an orbital polaron is observed, numerically and in an effective Hamiltonian. Double exchange in dilute magnetic semiconductors is studied using the coherent potential approximation (CPA)
Van, Den Berg Tineke. "Conductivité de spin et effets magnétiques dans les systèmes quantiques désordonnés". Electronic Thesis or Diss., Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4812.
Texto completo da fonteSpintronics is a research area that is concerned with the storage and transfer of information by means of electron spins. In the first part we investigated the intrinsic spin Hall effect in the presence of disordered magnetic impurities in a paramagnetic state in a two dimensional electron gas with Rashba spin-orbit coupling. In the presence of weak magnetic disorder the spin Hall conductivity stays close to its universal (clean system) value, as shown by analytical linear response calculations and numerical simulations. Heavy spin conductivity fluctuations are observed, that increase with disorder strength. To investigate the spreading of a wavepacket on a lattice we measure the wavepacket width, the inverse participation ratio and the (2)-fractal dimension. It is shown the system undergoes a localization transition at a critical disorder strength. In the localized regime the local density of states is not uniform anymore. An anti-ferromagnetic correlation between electron spins and impurity magnetic moments is observed. Beyond the localization transition the spin conductivity increases significantly. The first quantum (Cooperon) corrections in the linear response formalism are shown to contribute positively to the spin Hall conductivity. In the second part the double exchange Hubbard model for correlated electron systems is studied using dynamical mean field theory (DMFT) with the non-crossing approximation (NCA). Around quarter filling an orbital polaron is observed, numerically and in an effective Hamiltonian. Double exchange in dilute magnetic semiconductors is studied using the coherent potential approximation (CPA)
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.
Texto completo da fonteIn 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
Kulkarni, Giridhar. "Étude asymptotique des facteurs de formes des chaînes de spin quantiques". Thesis, Bourgogne Franche-Comté, 2020. http://www.theses.fr/2020UBFCK043.
Texto completo da fonteSince a long-time, the quantum integrable systems have remained an area where modern mathematical methods have given an access to interesting results in the study of physical systems. The exact computations, both numerical and asymptotic, of the correlation function is one of the most important subject of the theory of the quantum integrable models. In this context an approach based on the calculation of form factors has been proved to be a more effective one. In this thesis, we develop a new method based on the algebraic Bethe ansatz is proposed for the computation of the form-factors in thermodynamic limit. It is applied to and described in the context of isotropic XXX Heisenberg chain, which is one of the example of an interesting case of critical models where the Fermi-zone is non-compact
Jamonneau, Pierre. "Vers le développement de technologies quantiques à base de spins nucléaires dans le diamant". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLN052/document.
Texto completo da fonteAt a time where processing and exchanging big sets of data is one of the main challenge of our society, the development of technologies related to information based on the principles of quantum physics offer interesting new perspectives. This thesis is within the context of the emergence of new quantum technologies based on artificial atoms. We are particularly interested in the opportunities offered by single nuclear spins in diamond. The beginning of this thesis introduces the properties of the NV coloured center of diamond. In particular, we explain how the NV defect electronic spin can be used to detect nuclear spins dispersed in the diamond matrix. By making use, the anisotropic nature of the hyperfine interaction between the NV electron spin and 13C nuclear spins, we demonstrate nuclear spin initialization close to the nuclear spin levels anti-crossing. The specific structure of the spin system’s energy levels enables us to revisit the phenomenon of coherent population trapping with a single nuclear spin at room temperature. Finally, in the aim of developing new technologies based on this spin system, we describe the beginning of a project going towards the implementation of the micro-wave detection of a single electronic spin in diamond. This project is aiming to get rid of the optical illumination which is the main source of decoherence of the nuclear spin quantum state in diamond. The results obtained in this thesis about the control of spin systems in diamond, can be combined with the development of hybrid quantum systems. Thus, the combination of the long coherence time of nuclear spins with the computing performances of superconducting qu-bits is a promising development of quantum information technology
Flentje, Hanno. "Coherent transfer of electron spins in tunnel-coupled quantum dots". Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY039/document.
Texto completo da fonteRecent technological advances hint at the future possibility to use single electron spins as carriers and storage of information. Due to their quantum nature, individually controlled electron spins can not only be used to store classical information, but could also find implementation as quantum bits in a quantum computer. In this envisioned device, the superposition of different spin states could be used to perform novel calculation procedures more efficiently than their classical counterparts.A promising implementation of a controllable single electron spin system is an electron trapped in a lateral quantum dot. This nanoscale solid state device allows to isolate and coherently manipulate the spin of individual electrons with electrostatic potentials. In this thesis we study electrons in quantum dot structures using a manipulation technique which we call the "isolated regime". In this regime the manipulation of individual electron charges in several connected quantum dots is shown to be simplified. This allows to implement a novel spin manipulation scheme to induce coherent exchange of a quantum of spin between two electrons via a variation of the tunnel-coupling between adjacent quantum dots. This manipulation scheme is observed to lead to a reduced sensibility to charge noise at a "sweet spot" and thereby allows to obtain high quality spin oscillations.The improved charge control in the isolated regime is then used to achieve circular coupling in a triple quantum dot device with high tunnel-rates. This allows to directly probe the coherence of a superposition of two electron spins which are displaced on a closed loop in the three quantum dots. Our measurements demonstrate coherent electron transport over distances of up to 5 μm. During the transfer the coherence time is found to be significantly increased. We identify the underlying mechanism for the enhancement with a motional narrowing of the nuclear field gradients originating from the crystal environment. The limiting decoherence source is found to be single electron spin-flips induced by a real space motion of the electrons. Our results on the coherent transport of electrons can be used to asses the scaling possibilities of spin qubit implementations on two-dimensional lattices
Jadot, Baptiste. "Coherent long-range transport of entangled electron spins". Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALY007.
Texto completo da fonteQuantum computing is a field of growing interest, especially in Grenoble with an exceptional concentration of both research and industrials groups implicated in this field. The global aim is to develop a new kind of nano-processors, based on quantum properties. Its building brick is a two-level quantum system, in our case the spin of electrons trapped in a quantum dot.In this quest for a large-scale architecture, networked quantum computers offer a natural path towards scalability. Indeed, separating the computational task among quantum core units interconnected via a coherent quantum mediator would greatly simplify the addressability challenges. These quantum links should be able to coherently couple arbitrary nodes on fast timescales, in order to share entanglement across the whole quantum circuit. In semiconductor quantum circuits, nearest neighbor entanglement has already been demonstrated, and several schemes exist to realize long-range coupling. Among them, a possible implementation of this quantum mediator would be to prepare an entangled state and shuttle individual electron spins across the structure, provided that this transport preserves the entanglement.In this work, we demonstrate the fast and coherent transport of electron spin qubits across a 6.5 μm long channel, in a GaAs/AlGaAs laterally defined nanostructure. Using the moving potential induced by a propagating surface acoustic wave, we send sequentially two electron spins initially prepared in a spin singlet state. During its displacement, each spin experiences a coherent rotation due to spin-orbit interaction, over timescales shorter than any decoherence process. By varying the electron separation time and the external magnetic field, we observe quantum interferences which prove the coherent nature of both the initial spin state and the transfer procedure.We show that this experiment is analogous to a Bell measurement, allowing us to quantify the entanglement between the two electron spins when they are separated, and proving this fast and long-range qubit displacement is an efficient procedure to share entanglement across future large-scale structures
Dillenschneider, Raoul Richert Jean. "Effects of a strict site-occupation constraint in the description of quantum spin systems at finite temperature". Strasbourg : Université Louis Pasteur, 2006. http://eprints-scd-ulp.u-strasbg.fr:8080/560/01/DILLENSCHNEIDER2006.pdf.
Texto completo da fonteBaboux, Florent. "Effets spin-orbite géants sur les modes collectifs de spin de puits quantiques". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2013. http://tel.archives-ouvertes.fr/tel-01020564.
Texto completo da fonteJbeli, Anouar. "Dynamique de photoluminescence dans les boîtes quantiques auto-assemblées InGaAs/GaAs : propriétés de spin et couplage électronique inter-boîte". Toulouse, INSA, 2003. http://www.theses.fr/2003ISAT0015.
Texto completo da fonteRoubert, Benoît. "Approche semi-classique de l'information quantique". Toulouse 3, 2010. http://thesesups.ups-tlse.fr/1123/.
Texto completo da fonteToday, a large community of scientists is working to make possible the achievement of a quantum computer, a machine that can offer at least in theory (and especially for problems whose complexity grows exponentially with the size of the system) a degree of performance inaccessible to its classical counterpart. This thesis is looking at the possibility of producing a semi-classical approach of quantum information in two areas of interest: the cloning of a qubit, and the amplification of spin in spin chains. In the first part of this thesis is studied the role of interference in quantum cloners. We study in particular the case of cloners without interference (as defined, in the thesis) that turned out to be an intermediary case (that can be qualified of semi-classical) between purely quantum cloners (which propagate coherences and probabilities of density matrices) and classical cloners (which carry only the probabilities). In the second part, the phenomenon of amplification is studied in spin chains, which allows to amplify the state of a unique spin in a state of polarization of the entire chain, problem for which the semi-classical approach (valid because of the large number of spins) is used to show the unexpectedly important role played by the edge effects in these kind of systems
Regnault, Nicolas. "Solutions exactes de la gravité réduite : effet Hall quantique de spin". Phd thesis, Université Paris Sud - Paris XI, 2002. http://tel.archives-ouvertes.fr/tel-00001360.
Texto completo da fonteFlottat, Thibaut. "Bosons couplés à des spins 1/2 sur réseau". Thesis, Université Côte d'Azur (ComUE), 2016. http://www.theses.fr/2016AZUR4080/document.
Texto completo da fonteStrongly correlated systems, where new surprising phases of matter may appear both in the context of ultra-cold atoms and cavity quantum electrodynamics, are the focus of intense experimental and theoritical activity. In this thesis we present a study of two models of bosons with two or zero internal states, that is to say spin-1/2 or spin-0 bosons. These particles can move around a lattice, and they are locally coupled to immobile spins 1/2. Our interest was to determine the ground state phase diagram, study phase properties and quantum phase transitions. We used two methods: an approximate one using a mean field approach and the other using quantum Monte-Carlo simulations, which provides numerically exact results. The first model, namely the bosonic Kondo lattice model, is in the context of ultra-cold atoms in optical lattices. We found that its physics is close to that of the Bose-Hubbard model, exhibiting Mott and superfluid phases. The local coupling strengthens the insulating behaviour of the system and magnetism emerges through indirect or direct coupling between bosons. Thermal effects, inherent in experiments, are also studied. The second model, which is in the context of light-matter interaction, describes a situation of an ultra-strong coupling between spin-0 bosons (photons) and local spins 1/2 (two levels atoms) and is known as the Rabi lattice model. The phase diagram generally consists of only two phases: a coherent phase and a compressible incoherent one. The locals
Allen, Dave. "Étude des chaînes de spins par les méthodes de la théorie quantique des champs". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0004/NQ40506.pdf.
Texto completo da fonteAllen, Dave. "Étude des chaînes de spins par les méthodes de la théorie quantique des champs". Sherbrooke : Université de Sherbrooke, 1998.
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