Dissertations / Theses on the topic 'Entanglement in holography'

La notion d’entropie d’intrication a eu un profond impact sur la physique théorique, particulièrement depuis ces dix dernières années. D’abord introduite afin expliquer l’entropie des trous noirs, son champ d’application s’est par la suite ouvert à une grande variété de domaines de recherche, de la matière condensée à la gravitation quantique, de l’information quantique à la théorie quantique des champs. Dans ce contexte scientifique effervescent, l’entropie d’intrication apparait comme un outil central et doit donc intensivement être étudiée. A l’origine de cette thèse se trouve le désir de mieux comprendre cette entropie. D’intéressants développements concernant les effets de bord sur l’entropie d’intrication ont vu le jour récemment. Nous proposons donc d’explorer comment le bord d’un espace affecte l’entropie, en particulier dans la situation où la surface d’intrication intersecte ce bord. Nous présentons des calculs explicites de l’entropie d’intrication en espace plat avec bords. Nous montrons que des termes induits par ces bords apparaissent dans l’entropie et nous soulignons le rôle prépondérant que jouent les conditions aux bords. Nous étudions ensuite la contribution de bord dans le terme logarithmique de l’entropie d’intrication en dimensions trois et quatre. Nous calculons en premier lieu ce terme en théorie des champs pour la théorie N = 4 de Yang-Mills, puis nous répétons ce calcul de manière holographique. Nous montrons que ces deux méthodes de calcul donnent le même résultat, si du côté théorie des champs les conditions aux bords préservent la moitié de la supersymétrie et que du côté gravité l’extension du bord dans le bulk est une surface minimale
The entanglement entropy has had a tremendous and profound impact on theoretical physics, particularly since the last decade. First introduced in an attempt to explain black holes entropy, it has then found applications in a wide range of research areas, from condensed matter physics to quantum gravity, from quantum information to quantum field theory. In this exciting scientific context, the entanglement entropy has thus emerged as a useful and pivotal tool, and as such justifies the need to be intensively studied. At the heart of this thesis therefore lies the desire to better understand the entanglement entropy. Interesting developments during the recent years concern the boundary effects on the entanglement entropy. This dissertation proposes to explore the question of how the presence of spacetime boundaries affects the entropy, specifically in situations where the entangling surface intersects these boundaries. We present explicit calculations of entanglement entropy in flat spacetime with plane boundaries. We show that boundary induced terms appear in the entropy and we emphasize the prominent role of the boundary conditions. We then study the boundary contribution to the logarithmic term in the entanglement entropy in three and four dimensions. We perform the field theoretic computation of this boundary term for the free N = 4 super-gauge multiplet and then repeat the same calculation holographically. We show that these two calculations are in agreement provided that on the field theory side one chooses the boundary conditions which preserve half of the full supersymmetry and that on the gravity side the extension of the boundary in the bulk is minimal

In this thesis we will investigate a number of topics on the applications of the gauge-gravity duality to topics in condensed matter physics and quantum entanglement. This duality is a conjectured equivalence between type IIB string theory on asymptotically anti-de Sitter backgrounds with certain quantum field theories in one dimension less. Using this conjecture we can model strongly-coupled quantum systems using classical gravity duals which provide novel methods for calculating otherwise computationally inaccessible quantum properties. We will use this for the following applications: • We study a novel method for introducing broken translational symmetry into a holographic model whilst retaining homogeneity in the field equations. We demonstrate that this leads to a finite DC conductivity and shows features of heavy fermion models in the AC conductivity. • We explore the nature of real time scalar correlators in holographic models of critical systems that possess a non-relativistic scaling symmetry. Specifically we explore systems with dual Schrödinger or Lifshitz scaling symmetries, and discuss the problems that arise when trying to apply the standard framework of real time holography to these systems. • We provide an explicit counterexample to the holographic F-theorem, and an analytic argument that shows that this violation is not specific to the model in consideration but is rather a more general property of a class of holographic systems. • Finally we introduce a holographic renormalization scheme for the entanglement entropy based on the standard framework of holographic renormalization. We connect this to the field theory via the replica trick and use it to calculate a number of explicit examples both analytically and numerically.

In this thesis I explore the connection between geometry and quantum entanglement, in the context of holographic duality, where entanglement entropies in a quantum field theory are associated with the areas of surfaces in a dual gravitational theory. The first chapter looks at a phase transition in such systems in finite size and at finite temperature, associated with the properties of minimal surfaces in a static black hole background. This is followed by the related problem of extremal surfaces in a spacetime describing the dynamical process of black hole formation, with a view towards understanding the connections between bulk locality and various field theory observables including entanglement entropy. The third chapter looks at the simple case of pure gravity in three spacetime dimensions, where I show how evaluating the entanglement entropy can be reduced to a simple algebraic calculation, and apply it to some interesting examples. Finally, the role played by topology of surfaces in a proposed derivation of a holographic entanglement entropy formula is investigated. This makes it clear what assumptions are required in order to reproduce the ‘homology constraint’, a topological condition necessary for consistency with field theory.

In this thesis we study the time evolution of Rényi and entanglement entropies of thermal states in Conformal Field Theory (CFT). These quantities are usually hard to compute but Ryu-Takayanagi (RT) and Hubeny-Rangamani-Takayanagi (HRT) proposals allow us to find the same quantities using calculations in general relativity. We will introduce main concepts of holography, quantum information and conformal field theory that will be used to derive the results of this thesis. In the first part of the thesis, we explicitly compute entanglement entropy of the rotating BTZ black hole by directly applying HRT proposal and finding lengths of spacelike geodesics. Rényi entropy of thermal state perturbed by a local quantum quench is computed by mapping correlators on two glued cylinders to the plane for field theory containing a single free boson and for 2d CFTs in the large c limit. We consider Thermofield Double State (TFD) which is an entangled state in direct product of two 2D CFTs. It is conjectured to be holographically equivalent to the eternal BTZ black hole. TFD state is perturbed by a local quench in one CFT and mutual information between two intervals in two CFTs is computed. We find when mutual information vanishes and interpret this as scrambling time, i.e. time scale required for the system to thermalize. This field theory result is modelled with a massive free falling particle in the BTZ black hole. We have computed the back-reaction of the particle on the metric of BTZ and used RT proposal to find holographic entanglement entropy. Finally, we generalize this calculation to the case of rotating BTZ with inner and outer horizons. It is dual to the CFT with different temperatures for left and right moving modes. We calculate mutual information and scrambling time and find exact agreement between results in the gravity and those in the CFT.

Recentemente, uma quantidade de informação/computação quântica chamada complexidade computacional tem adquirido mais e mais importância no estudo de buracos negros.Resumidamente, complexidade mede a dificuldade de alguma tarefa. No contexto de mecânica quântica (ou mesmo para estados em uma CFT), qualquer estado tem uma complexidade associada, uma vez que o processo de preparar algum estado, usando operações unitárias, é uma tarefa por sí só. Propostas holográficas para o cálculo de complexidade tem sido desenvolvidas nos anos recentes. Há duas delas que estão mais desenvolvidas: as conjecturas complexidade=volume e complexidade=ação. No contexto da correspondência AdS/CFT é sabido que o buraco negro de Schwarzschild em AdS é dual à um estado térmico que descreve duas CFTs emaranhadas. Para esse caso em específico, a conjectura complexidade=volume iguala a complexidade do estado que descreve esse par de CFTs emaranhadas com o volume da máxima superfície de codimensão um no espaço-tempo dual. Por outro lado, a conjectura complexidade=ação iguala a complexidade da borda com a ação gravitacional calculada sobre uma região do espaço-tempo conhecida como Wheeler-DeWitt patch. O objetivo dessa tese é proporcionar os requisitos necessários para entender as conjecturas relacionadas com complexidade, monstrando alguns resultados importantes proporcionados pelos cálculos holográficos no lado gravitacional.
In recent years, a quantity from quantum information/computation called computational complexity has been acquiring more and more importance in the study of black holes. Briefly, complexity measures the hardness of some task. In the context of quantum mechanics (or even for states in a CFT), any state has an associated complexity, once the process of to preparing some state, using unitary operations, is a task by itself. Holographic proposals for the computation of complexity have been developed in recent years. There are two of them that are more developed: the complexity=volume and complexity=action conjectures. In the context of the AdS/CFT correspondence, it is known that the two sided AdS-Schwarzschild black hole is dual to some thermal state that describes two entangled CFTs. For this specific case, the complexity=volume conjecture equates the complexity of the state that describes this pair of entangled CFTs with the volume of the maximal codimension-one surface in the dual space-time. On the other hand, the complexity=action conjecture equates the boundary complexity with the gravitational action evaluated on a region of space-time known as the Wheeler-DeWitt patch. The goal of this thesis is to provide the necessary requisites to understand the conjectures related to complexity, showing some important results provided by holographic computations on the gravitational side.

The work presented in this thesis is a contribution towards the understanding of holo- graphic entanglement from an operational perspective. Following the interpretation which is most natural for quantum information theory, entanglement is viewed as a resource that can be produced, stored, transferred and used for practical purposes. The first chapter introduces the main concepts which are necessary throughout the discussion. Quantum entanglement, as opposed to merely classical correlation, is presented in detail within the framework of quantum mechanics. This is followed by a brief overview on the current state of knowledge about entanglement in quantum field theory and more specifically in gauge/gravity duality. The second chapter investigates a particular measure of entanglement, known as nega- tivity, in the context of holographic field theories. This is further explored in the following (third) chapter, where an interesting dependence of the entanglement between a region and its complement on the topology of their interface is presented. The forth chapter investigates qubits systems and compares equivalence classes of entanglement structures to known properties of holographic states. The fifth chapter focuses on the behaviour of the tripartite information for highly en- tangled states, both in a bipartite and multipartite sense, in relation to the sign definiteness imposed by holography. A final chapter comments on future directions of investigation within this program.

One decade ago, Ryu-Takayanagi explicitly introduced a formula that relates the entropy of a subregion in CFT system to a geometrical quantity which is called minimal surface in hyperbolic space. This formula extended to the idea of connection of gravy to quantum mechanics of gauge/gravity duality. This duality which can help us to learn a more interesting feature of each side from the other. Quantum systems obey from some constraints come from the quantum information theory. I would be interesting to find out what is the dual of this constraint in the gravitation system. Dual to the specific class of quantum theories which is called conformal field theories. One of the most significant constraint that QFTs should obey is the strong subadditivity of entanglement entropy. These constraints let the theories have bound on the energy spectrum from the below; Recently there has been the development that the combination of monotonicity of relative entropy and the strong subadditivity of entanglement entropy is equal to have a specific bound on the energy momentum tensor, called quantum null energy condition. In this thesis, we re-look to this argument by introducing the entanglement density and obtain a differential operator from the strong subadditivity and exploiting from the Markov property of the vacuum of CFT. In the next step, by using from the Ryu-Takayangi, we rewrite the strong subadditivity inequality regarding geometrical quantities. By using from the kinematic languages and intertwinement, we realize that the strong subadditivity at the boundary implies new bound on averaged energy condition which has some common feature with the quantum null energy condition statement.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

The holographic Ryu-Takayanagi formula for entanglement entropy connects the entanglement of a field theory to the geometry of a dual gravitational theory in a straightforward and universal way. The first part of this thesis applies this formula to study the entanglement entropy in strongly coupled noncommutative field theories. It is found that the ground state of these theories have substantial entanglement at the length scale of the noncommutativity. The entanglement entropy in a different perturbative regime is also computed, where in contrast it is found that noncommutative interactions do not induce long range entanglement in the ground state to leading order in perturbations theory. The second part of this thesis explores some general consequences of this holographic formula for the entanglement entropy. Identities involving entanglement entropies are related to nontrivial geometric constraints on gravitational duals. In particular, the strong subadditivity of entanglement entropy is used to show that dual three dimensional asymptotically anti-de Sitter gravitational states must obey an averaged null energy condition. Finally, this holographic formula allows us at least in principle to express the entanglement entropy of a region in a holographic field theory in terms of the one-point functions in that theory. This is explored in the context of a two dimensional conformal field theory where explicit calculations are possible. Our results in this case allow us to extend a recent proposal that the entanglement entropy of states near the vacuum of conformal theories can be understood by propagation in an auxiliary de Sitter space.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

The idea of holography [1, 2] finds a concrete realization in form of the AdS/CFT correspondence [3, 4]. This duality relates a field theory with conformal symmetries to quantum gravity living in one higher dimension. In this thesis we study aspects of black hole quasinormal modes, higher spin theories and entanglement entropy in the context of this duality. In almost all cases we have been able to subject the duality to some precision tests. Quasinormal modes encode the spectrum of black holes and the time-scale of pertur- bations therein [5]. From the dual CFT viewpoint they are the poles of retarded Green's function (or peaks in the spectral function) [6]. Quasinormal modes were previously studied for scalar, gauge field and fermion fluctuations [7]. We solve for these quasinormal modes of higher spin (s _ 2) fields in the background of the BTZ black hole [8, 9]. We obtain an exact solution for a field of arbitrary spin s (integer or half-integer) in the BTZ background. This implies that the BTZ is perhaps the only known black hole background where such an analysis can be done analytically for all bosonic and fermionic fields. The quasinormal modes are shown to match precisely with the poles of the corresponding Green's function in the CFT living on the boundary. Furthermore, we show that one-loop determinants of higher spin fields can also be written as a product form [10] in terms of these quasinormal modes and this agrees with the same obtained by integrating the heat-kernel [11]. We then turn our attention to dualities relating higher-spin gravity to CFTs with W algebra symmetries. Since higher spin gravity does go beyond diffeomorphism invariance, one needs re_ned notions of the usual concepts in differential geometry. For example, in general relativity black holes are defined by the presence of the horizon. However, higher spin gravity has an enlarged group of symmetries of which the diffeomorphisms form a subgroup. The appropriate way of thinking of solutions in higher spin gravity is via characterizations which are gauge invariant [12, 13]. We study classical solutions embedded in N = 2 higher spin supergravity. We obtain a general gauge-invariant condition { in terms of the odd roots of the superalgebra and the eigenvalues of the holonomy matrix of the background { for the existence of a Killing spinor such that these solutions are supersymmetric [14]. We also study black holes in higher spin supergravity and show that the partition function of these black holes match exactly with that obtained from a CFT with the same asymptotic symmetry algebra [15]. This involved studying the asymptotic symmetries of the black hole and thereby developing the holographic dictionary for the bulk charges and chemical potentials with the corresponding quantities of the CFT. We finally investigate entanglement entropy in the AdS3/CFT2 context. Entanglement entropy is an useful non-local probe in QFT and many-body physics [16]. We analytically evaluate the entanglement entropy of the free boson CFT on a circle at finite temperature (i.e. on a torus) [17]. This is one of the simplest and well-studied CFTs. The entanglement entropy is calculated via the replica trick using correlation functions of bosonic twist operators on the torus [18]. We have then set up a systematic high temperature expansion of the Renyi entropies and determined their finite size corrections. These _nite size corrections both for the free boson CFT and the free fermion CFT were then compared with the one-loop corrections obtained from bulk three dimensional handlebody spacetimes which have higher genus Riemann surfaces (replica geometry) as its boundary [19]. One-loop corrections in these geometries are entirely determined by the spectrum of the excitations present in the bulk. It is shown that the leading _nite size corrections obtained by evaluating the one-loop determinants on these handlebody geometries exactly match with those from the free fermion/boson CFTs. This provides a test for holographic methods to calculate one-loop corrections to entanglement entropy. We also study conformal field theories in 1+1 dimensions with W-algebra symmetries at _nite temperature and deformed by a chemical potential (_) for a higher spin current. Using OPEs and uniformization techniques, we show that the order _2 correction to the Renyi and entanglement entropies (EE) of a single interval in the deformed theory is universal [20]. This universal feature is also supported by explicit computations for the free fermion and free boson CFTs { for which the EE was calculated by using the replica trick in conformal perturbation theory by evaluating correlators of twist fields with higher spin operators [21]. Furthermore, this serves as a verification of the holographic EE proposal constructed from Wilson lines in higher spin gravity [22, 23]. We also examine relative entropy [24] in the context of higher-spin holography [25]. Relative entropy is a measure of distinguishability between two quantum states. We confirm the expected short-distance behaviour of relative entropy from holography. This is done by showing that the difference in the modular Hamiltonian between a high-temperature state and the vacuum matches with the difference in the entanglement entropy in the short-subsystem regime.

abstract: Here I develop the connection between thermodynamics, entanglement, and gravity. I begin by showing that the classical null energy condition (NEC) can arise as a consequence of the second law of thermodynamics applied to local holographic screens. This is accomplished by essentially reversing the steps of Hawking's area theorem, leading to the Ricci convergence condition as an input, from which an application of Einstein's equations yields the NEC. Using the same argument, I show logarithmic quantum corrections to the Bekenstein-Hawking entropy formula do not alter the form of the Ricci convergence condition, but obscure its connection to the NEC. Then, by attributing thermodynamics to the stretched horizon of future lightcones -- a timelike hypersurface generated by a collection of radially accelerating observers with constant and uniform proper acceleration -- I derive Einstein's equations from the Clausius relation. Based on this derivation I uncover a local first law of gravity, connecting gravitational entropy to matter energy and work. I then provide an entanglement interpretation of stretched lightcone thermodynamics by extending the entanglement equilibrium proposal. Specifically I show that the condition of fixed volume can be understood as subtracting the irreversible contribution to the thermodynamic entropy. Using the AdS/CFT correspondence, I then provide a microscopic explanation of the 'thermodynamic volume' -- the conjugate variable to the pressure in extended black hole thermodynamics -- and reveal the super-entropicity of three-dimensional AdS black holes is due to the gravitational entropy overcounting the number of available dual CFT states. Finally, I conclude by providing a recent generlization of the extended first law of entanglement, and study its non-trivial 2+1- and 1+1-dimensional limits. This thesis is self-contained and pedagogical by including useful background content relevant to emergent gravity.
Dissertation/Thesis
Doctoral Dissertation Physics 2020

Vrije Universiteit Brussel - THEORETISCHE NATUURKUNDE Applications of the AdS/CFT correspondence to strongly coupled dynamics Dissertation presented in partial fulfillment of the requirements for the degree Doctor of Science Brussels, May 2012 PhD advisors: Prof. Dr. B. Craps and Prof. Dr. A. Sevrin (Theoretische Natuurkunde, Vrije Universiteit Brussel, Belgium) Members of the Jury: Prof. Dr. I. Veretennicoff, chairperson (Natuurkunde & Toegepaste Natuurkunde & Fotonica, Vrije Universiteit Brussel, Belgium) Prof. Dr. N. Van Eijndhoven, secretary (IIHE, Vrije Universiteit Brussel, Belgium) Prof. Dr. J. L. F. Barbón (Instituto de F ́ısica Te ́orica, UAM/CSIC, Spain) Prof. Dr. F. Blekman (IIHE, Vrije Universiteit Brussel, Belgium) Prof. Dr. F. Denef (Instituut voor Theoretische Fysica, Katholieke Universiteit Leuven, Belgium)

Over the past decade, the AdS/CFT correspondence has proven to be a remarkable tool to study various properties of strongly coupled field theories. In the context of the holography, Ryu and Takayanagi have proposed an elegant method to calculate entanglement entropy for these field theories. In this thesis, we use this holographic entanglement entropy to study a candidate c-theorem and entanglement entropy for singular surfaces. We use holographic entanglement entropy for strip geometry and construct a candidate c-function in arbitrary dimensions. For holographic theories dual to Einstein gravity, this c-function is shown to decrease monotonically along RG flows. A sufficient condition required for this monotonic flow is that the stress tensor of the matter fields driving the holographic RG flow must satisfy the null energy condition over the holographic surface used to calculate the entanglement entropy. In the case where the bulk theory is described by Gauss-Bonnet gravity, the latter condition alone is not sufficient to establish the monotonic flow of the c-function. We also observe that for certain holographic RG flows, the entanglement entropy undergoes a ‘phase transition’ as the size of the system grows and as a result, evolution of the c-function may exhibit a discontinuous drop. Then, we turn towards studying the holographic entanglement entropy for regions with a singular boundary in higher dimensions. Here, we find that various singularities make new universal contributions. When the boundary CFT has an even spacetime dimension, we find that the entanglement entropy of a conical surface contains a term quadratic in the logarithm of the UV cut-off. In four dimensions, the coefficient of this contribution is proportional to the central charge c. A conical singularity in an odd number of spacetime dimensions contributes a term proportional to the logarithm of the UV cut-off. We also study the entanglement entropy for various boundary surfaces with extended singularities. In these cases, extended singularities contribute through new linear or quadratic terms in logarithm only when the locus of the singularity is even dimensional and curved.

博士
國立臺灣師範大學
物理學系
105
Two topics on entanglement are concerned in this thesis: One is the decoherence patterns of a topological qubit made of two Majorana zero modes in the generic linear and circular motions and the other is a simplified protocol of quantum energy teleportation (QET) for the holographic conformal field theory in three-dimensional anti-de Sitter space with or without a black hole. On the first topic, the exact reduced dynamics without Markov approximation is shown. For general time scale, the acceleration causes thermalization as expected by Unruh effect. However, for the short-time scale, the rate of decoherence is anti-correlated with the acceleration, as a kind of decoherence impedance. This is in fact related to the “anti-Unruh" phenomenon previously found by studying the transition probability of Unruh-DeWitt detector. Besides, the information backflow is observed by some time modulations of coupling constant or acceleration. Moreover, it also shows that some incoherent accelerations of the constituent Majorana zero modes can preserve the coherence instead of thermalizing it. On the second topic, as a tentative proposal, the standard QET is simplified by replacing Alice’s local measurement with the local projection. At the same time, Bob’s local operation of the usual QET for extracting energy is mimicked by deforming the UV surface with a local bump. Adopting the surface-state duality, this deformation corresponds to local unitary. In this protocol, the extraction energy is always positive. Moreover, the ratio of extraction energy to the injection one is an universal function of the UV surface deformation profile.

This thesis presents a series of studies of thermalization and dissipation in a variety of strongly coupled systems. The main tool for these investigations is the Gauge/Gravity duality, which establishes a correspondence between a d+1-dimensional quantum theory of gravity and a d-dimensional quantum field theory. We study the decay rates of fluctuations around the thermal equilibrium in theories in non-commutative geometry. Rapid thermalization of such fluctuations is found and motivates the conjecture that the phenomena at the black hole horizon is described by non-local physics. In the same type of environment, we analyze the Langevin dynamics of a heavy quark, which undergoes Brownian motion. We find that the late-time behavior of the displacement squared is unaffected by the non-commutativity of the geometry. In a different scenario, we study the correlation functions in theories with quantum critical points. We compute the response of these quantum critical points to a disturbance caused by a massive charged particle and analyze its late time behavior. Finally, we analyze systems far-from-equilibrium as they evolve towards a thermal state. We characterize this evolution for systems with chemical potential by focusing on the ``strong subadditivity" property of their entanglement entropy. This is achieved on the gravity side by using time dependent functions for mass and charge in an AdS-Vaydia metric.
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