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Quantum information theory is a branch of science at the frontier of physics, mathematics, and information science, and offers a variety of solutions that are impossible using classical theory. This book provides a detailed introduction to the key concepts used in processing quantum information and reveals that quantum mechanics is a generalisation of classical probability theory. The second edition contains new sections and entirely new chapters: the hot topic of multipartite entanglement; in-depth discussion of the discrete structures in finite dimensional Hilbert space, including unitary operator bases, mutually unbiased bases, symmetric informationally complete generalized measurements, discrete Wigner function, and unitary designs; the Gleason and Kochen-Specker theorems; the proof of the Lieb conjecture; the measure concentration phenomenon; and the Hastings' non-additivity theorem. This richly-illustrated book will be useful to a broad audience of graduates and researchers interested in quantum information theory. Exercises follow each chapter, with hints and answers supplied.

Quantum theory. --- Quantum entanglement.

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This book presents a complete study of natural orbitals in quantum impurity problems, revealing a certain simplicity in these interacting many-body problems. These systems consist of a few localized degrees of freedom that undergo strong interactions and hybridize with a larger system of free particles; they are central in the study of strongly correlated systems. In a first step, the standard non-perturbative numerical renormalization group method is employed to demonstrate the hierarchical structure of correlations unveiled by natural orbitals. This simplification brought new insights for simulating quantum impurity problems, and a new algorithm is developed to generate an optimized subset of natural orbitals independently of existing methods, going beyond their usual limitations. This algorithm is presented in detail in the book, and a careful benchmark on known results is carried out to guarantee the validity of the method. It is then used to study spatialentanglement structures under various conditions that were not accessible with previous methods, such as representing the electron bath by a realistic 2D square lattice or taking account of static disorder in the metallic host. In the last chapter, the non-interacting problem in the presence of disorder is studied through random matrix theory, reproducing some of the results presented in the previous chapters. The main original result of this chapter lies in the analytical calculation of the joint distribution of one-particle orbitals energies and amplitudes of the impurity, which makes it possible to calculate any disordered averaged local correlation functions. Starting from this result, calculations in the large-N limit are compared with numerical simulations.

Quantum physics. --- Electronics --- Quantum entanglement. --- Quantum Physics. --- Electronic Materials. --- Quantum Correlation and Entanglement. --- Materials. --- Quantum theory.

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The purpose of this book is to empower readers to deeply understand how quantum-entangled particles violate common-sense assumptions and constraints. This book focuses on what quantum physics is not and investigates seemingly plausible theories that cannot account for experimental results. Quantum physics is notable for its brazen defiance of common sense. (Think of Schrödinger's Cat, famously both dead and alive). An especially rigorous form of quantum contradiction occurs in experiments with entangled particles. Our common assumption is that objects have properties whether or not anyone is observing them, and the measurement of one can't affect the other. Quantum entanglement - called by Einstein "spooky action at a distance" - rejects this assumption, offering impeccable reasoning and irrefutable evidence of the opposite. Is quantum entanglement mystical, or just mystifying ? In this volume in the MIT Press Essential Knowledge series, Jed Brody equips readers to decide for themselves. He explains how our commonsense assumptions impose constraints - from which entangled particles break free.Brody explores such concepts as local realism, Bell's inequality, polarization, time dilation, and special relativity. He introduces readers to imaginary physicists Alice and Bob and their photon analyses ; points out that it's easier to reject falsehood than establish the truth ; and reports that some physicists explain entanglement by arguing that we live in a cross-section of a higher-dimensional reality. He examines a variety of viewpoints held by physicists, including quantum decoherence, Niels Bohr's Copenhagen interpretation, genuine fortuitousness, and QBism. This relatively recent interpretation, an abbreviation of "quantum Bayesianism," holds that there's no such thing as an absolutely accurate, objective probability "out there," that quantum mechanical probabilities are subjective judgments, and there's no "action at a distance," spooky or otherwise.

Quantum entanglement. --- Relativity (Physics) --- Théorie quantique. --- Relativité (physique) --- Quantum entanglement --- Entangled states (Quantum theory) --- Quantum theory --- Entanglement (Quantum theory) --- Théorie quantique. --- Relativité (physique)

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Characterizing entanglement is an important issue in quantum information, as it is considered to be a resource for many applications such as quantum key distribution or quantum metrology. One useful tool to detect and quantify entanglement are witness operators. A standard way to construct them is based on the fidelity of pure states and mathematically relies on the Schmidt decomposition of vectors. In this book a method to build entanglement witnesses using the Schmidt decomposition of operators is presented. One can show that these are strictly stronger than the fidelity witnesses. Moreover, the concept can be generalized easily to the multipartite case, and one may use it to quantify the dimensionality of entanglement. Finally, this scheme will be used to provide two algorithms that can be combined to improve given witnesses for multiparticle entanglement. About the author Sophia Denker studied physics at the University of Siegen. Now she is investigating concepts of high dimensional entanglement under the tutelage of Prof. Dr. Otfried Gühne. Her master thesis was awarded with the “Studienpreis des Landkreises Altenkirchen 2023”.

Quantum physics. --- Quantum computing. --- Quantum Physics. --- Quantum Information. --- Quantum entanglement.

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This book uses the formal semantics of counterfactual conditionals to analyze the problem of non-locality in quantum mechanics. Counterfactual conditionals (subjunctive conditionals) enter the analysis of quantum entangled systems in that they enable us to precisely formulate the locality condition that purports to exclude the existence of causal interactions between spatially separated parts of a system. They also make it possible to speak consistently about alternative measuring settings, and to explicate what is meant by quantum property attributions. The book develops the possible-world semantics of quantum counterfactuals using David Lewis's famous approach as a starting point but modifying it significantly in order to achieve compatibility with the demands of the special theory of relativity as well as quantum mechanics. There have been several attempts to use counterfactual semantics to strengthen Bell's theorem and its cognates such as the GHZ and Hardy theorems. These are critically evaluated in the book. Finally, a counterfactual reconstruction of the EPR argument and Bell's theorem is proposed that sheds a new light on their philosophical consequences regarding the relations between realism and local causation.

Cosmology. --- Philosophy. --- Quantum theory. --- Quantum theory --- Quantum entanglement --- Physics --- Physical Sciences & Mathematics --- Atomic Physics --- Quantum entanglement. --- Entangled states (Quantum theory) --- Quantum dynamics --- Quantum mechanics --- Quantum physics --- Mechanics --- Thermodynamics --- Entanglement (Quantum theory)