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Çok Parçalı Sistemlerde Korelasyonlara Kuantum Bilişimi Yaklaşımı

Aksak, Çağan

Published Oct 27, 2022• 0 citations
OpenAlex

Abstract

Quantum correlations are crucial features in both quantum information theory and many-body physics. Characterization and quantification of quantum correlations have delivered a rich body of work and helped to understand some quantum phenomena. Entanglement is a unique quantum correlation for which it is a resource in many quantum information tasks. Developed for quantification of entanglement, entanglement witness formalism is a remarkable tool in the quantum information toolkit. It can be deployed beyond the entanglement theory to quantify quantum correlations in many-body systems. For many-body systems, the particle statistics and indistinguishability are essential. The relation between indistinguishability and entanglement has to be studied carefully. In this thesis, first, a class of witness operators for pairing correlations in both fermionic and bosonic systems have been proposed and the necessary and sufficient conditions for being a witness operator are found. Then, a Clauser-Horne-Shimony-Holt type test and its bounds for fermions have been demonstrated.

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Quantum correlations are crucial features in both quantum information theory and many-body physics. Characterization and quantification of quantum correlations have delivered a rich body of work and helped to understand some quantum phenomena. Entanglement is a unique quantum correlation for which it is a resource in many quantum information tasks. Developed for quantification of entanglement, entanglement witness formalism is a remarkable tool in the quantum information toolkit. It can be deployed beyond the entanglement theory to quantify quantum correlations in many-body systems. For many-body systems, the particle statistics and indistinguishability are essential. The relation between indistinguishability and entanglement has to be studied carefully. In this thesis, first, a class of witness operators for pairing correlations in both fermionic and bosonic systems have been proposed and the necessary and sufficient conditions for being a witness operator are found. Then, a Clauser-Horne-Shimony-Holt type test and its bounds for fermions have been demonstrated.
Quantum correlations and entanglement in identical-particle systems have been a puzzling question which has attracted vast interest and widely different approaches. Witness formalism developed first for entanglement measurement can be adopted to other kind of correlations. An approach is introduced by Kraus \emph{et al.}, [Phys. Rev. A \textbf{79}, 012306 (2009)] based on pairing correlations in fermionic systems and the use of witness formalism to detect pairing. In this contribution, a two-particle-annihilation operator is used for constructing a two-particle observable as a candidate witness for pairing correlations of both fermionic and bosonic systems. The corresponding separability bounds are also obtained. Two different types of separability definition are introduced for bosonic systems and the separability bounds associated with each type are discussed.
An entangled state of a two-particle system is a quantum state that cannot be separated-it cannot be written as the product of states of the individual particles.One way to tell if a system is entangled is to use it to violate a Bell inequality (such as the Clauser-Horne-Shimony-Holt, CHSH, inequality), because entanglement is necessary to violate these inequalities.However, there are other, more efficient measurements that determine whether or not a system is entangled; an operator that corresponds to such a measurement is referred to as an entanglement witness.We present the theory of witness operators, and an undergraduate experiment that measures an entanglement witness for the joint polarization state of two photons.We are able to produce states for which the expectation value of the witness operator is entangled by more than 160 standard deviations.
Quantum correlations and entanglement in identical-particle systems have been a puzzling question which has attracted vast interest and widely different approaches. A novel approach is introduced by Kraus \emph{et al.}, [Phys. Rev. A \textbf{79}, 012306 (2009)] based on pairing correlations in fermionic systems and the use of witness formalism to detect pairing. In this contribution, this approach has been extended to bosonic systems and separability bounds based on pairing correlations for fermions and bosons have been obtained. A two-particle annihilation operator is used for constructing a two-particle observable as a candidate witness. Two different types of separability definition is introduced for bosonic systems and the separability bounds associated with each type are discussed.
An entangled state of a two-particle system is a quantum state that cannot be separated, meaning it cannot be written as the product of states of the individual particles. One way to tell if a system is entangled is to use it to violate a Bell inequality (such as the Clauser-Horne-Shimony-Holt, CHSH, inequality), because entanglement is necessary for such a violation. However, there are other, easier-to-perform measurements that determine whether or not a system is entangled. An operator that corresponds to such a measurement is referred to as an entanglement witness. Here, we present the theory of witness operators and an undergraduate experiment that measures entanglement witnesses for the joint polarization state of two photons. We are able to produce states for which the expectation value of a witness operator is entangled by more than 300 standard deviations. In order to further examine the performance of these witness operators, we present a simple way to generate states that closely approximate Werner states, which have a controllable degree of entanglement.
We present here an overview of our work concerning entanglement properties of composite quantum systems. The characterization of entanglement, i.e. the possibility to assert if a given quantum state is entangled with others and how much entangled it is, remains one of the most fundamental open questions in quantum information theory. We discuss our recent results related to the problem of separability and distillability for distinguishable particles, employing the tool of witness operators. Finally, we also state our results concerning quantum correlations for indistinguishable particles.
The study of entanglement in systems composed of identical particles raises interesting challenges with far-reaching implications in both, our fundamental understanding of the physics of composite quantum systems, and our capability of exploiting quantum indistinguishability as a resource in quantum information theory. Impressive theoretical and experimental advances have been made in the last decades that bring us closer to a deeper comprehension and to a better control of entanglement. Yet, when it involves composites of indistinguishable quantum systems, the very meaning of entanglement, and hence its characterization, still finds controversy and lacks a widely accepted definition. The aim of the present paper is to introduce, within an accessible and self-contained exposition, the basic ideas behind one of the approaches advanced towards the construction of a coherent definition of entanglement in systems of indistinguishable particles, with focus on fermionic systems. We also inquire whether the corresponding tools developed for studying entanglement in identical-fermion systems can be exploited when analysing correlations in distinguishable-party systems, in which the complete information of the individual parts is not available. Further, we open the discussion on the broader problem of constructing a suitable framework that accommodates entanglement in the presence of generalized statistics. This article is part of the theme issue 'Identity, individuality and indistinguishability in physics and mathematics'.