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Distribution and quantum coherence manipulation in multi-qudit systems

Lucas Camponogara Viera

Published Feb 24, 2017• 0 citations
OpenAlex

Abstract

Repeatedly in the field of Quantum Information Science (QIS) it’s essentially required of physical systems the quantification concerning its quantum phenomena, such as Quantum Coherence (QC) relying in quantum superposition states. Hereafter several quantifiers of QC have been proposed over the years through distance measures in quantum state spaces, called distinguishability measures, playing an important role in QIS correlation phenomena such as Discord and Entanglement with Quantum Cryptography implementation, as example. The aim of this dissertation is to extend the research of QC, published by Jonas Maziero in an article, performing an in-depth analysis regarding the control of local and non-local aspects of Hilbert-Schmidt Coherence (HSC) in multipartite systems and its relations with others QC quantifiers, as well as an analisys of a possible Hilbert-Schmidt Distance (HSD) implication in QC functions over the Non-Monotonicity under Tensor Products (NMuTP) inequality and of limitations between Coherence of state populations and energy. Starting from the generic multipartite state of level quantum energy systems (qudit), defined from the Bloch parameterization, calculations of QC functions concerning its particular cases are considered for 1-qubit, 2-qubit, 1-qutrit and two copies of 1-qubit adopting HSD. Writing the HSC function for the latter case in terms of its local and non-local parts and from the result of 1-qubit it is possible, by manipulating the difference between local populations, to infer a non-local implication in the HSC for that system, in contrast to what has been seen by adopting distinct dissimilarity measures for this function, named l1- Norm Distance and Relative Entropy Distance, cases where there are no implications and where there is a direct consequence with their local populations instead of the previously difference between them, respectively. Notwithstanding, HSD usage provides a description of an awkward relation in QIS towards NMuTP, and a possible implication of that kind of relation in QIS emergent phenomena such as QC function.

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Repeatedly in the field of Quantum Information Science (QIS) it’s essentially required of physical systems the quantification concerning its quantum phenomena, such as Quantum Coherence (QC) relying in quantum superposition states. Hereafter several quantifiers of QC have been proposed over the years through distance measures in quantum state spaces, called distinguishability measures, playing an important role in QIS correlation phenomena such as Discord and Entanglement with Quantum Cryptography implementation, as example. The aim of this dissertation is to extend the research of QC, published by Jonas Maziero in an article, performing an in-depth analysis regarding the control of local and non-local aspects of Hilbert-Schmidt Coherence (HSC) in multipartite systems and its relations with others QC quantifiers, as well as an analisys of a possible Hilbert-Schmidt Distance (HSD) implication in QC functions over the Non-Monotonicity under Tensor Products (NMuTP) inequality and of limitations between Coherence of state populations and energy. Starting from the generic multipartite state of level quantum energy systems (qudit), defined from the Bloch parameterization, calculations of QC functions concerning its particular cases are considered for 1-qubit, 2-qubit, 1-qutrit and two copies of 1-qubit adopting HSD. Writing the HSC function for the latter case in terms of its local and non-local parts and from the result of 1-qubit it is possible, by manipulating the difference between local populations, to infer a non-local implication in the HSC for that system, in contrast to what has been seen by adopting distinct dissimilarity measures for this function, named l1- Norm Distance and Relative Entropy Distance, cases where there are no implications and where there is a direct consequence with their local populations instead of the previously difference between them, respectively. Notwithstanding, HSD usage provides a description of an awkward relation in QIS towards NMuTP, and a possible implication of that kind of relation in QIS emergent phenomena such as QC function.
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This dissertation describes the application of symmetry to multipartite quantum systems from the viewpoint of quantum information theory. It is written in the framework of abstract quantum information theory, i.e. without distinguishing the physical nature of the d-level systems considered. The results are mathematically rigorous and aim at investigating entanglement properties as well as operational properties of states of multipartite systems. The first chapter gathers the mathematical tools and concepts needed in the following chapters and can be omitted by the experienced reader. In chapter two we apply the concept of symmetry to multipartite systems and show how to construct families of symmetric states that can be described by few parameters only regardless of the size of single systems. Chapter three is devoted to the states of tripartite systems having Werner symmetry. We characterize their separability properties and analyze the strength of the known separability criteria. Furthermore we investigate their entanglement properties in terms of the relative entropy of entanglement, the entanglement monotone induced by the trace norm distance and the maximal violation of Bell inequalities. As a third aspect we analyze the possibility of embedding bipartite Werner states and explore the inner geometry of the manifold given by the statistical distance of two neighbouring tripartite Werner states. In the fourth chapter we introduce multipartite quantum data hiding as an application of multipartite Werner states. We prove the security of this protocol for any coalition and give various examples. The last chapter is concerned with the shared fidelity, its frustration and how it can be maximized in certain multipartite systems.
Quantum computing is among the most far-reaching technologies of the 21st century, tackling challenges at the cutting edge of physics. This new paradigm in computer science harnesses quantum entanglement, one striking non-intuitive feature of quantum mechanics and a cornerstone of quantum information, to provide computation with a quantum speed-up over the best-known classical algorithms and to enable encrypted data communication against eavesdropping. The bulk of this article is focused on providing a deep and abiding understanding of non-relativistic matrix mechanics by demonstrating the fundamental mathematical identities of the contemporary postulatory approach of quantum mechanics within the state vector and density operator formalism in multipartite systems. In addition to that, we derive and analyze the respective 1-qubit, 1-qutrit, 2-qubit, and 2-qudit coherent and incoherent density operators using Bloch's parametrization for generalized ddd-dimensional NNN-qudit states embedded in the SU(d)SU(d)SU(d) Lie group with associate generalized Gell Mann's matrices spanning the su(d)\mathfrak{su}(d)su(d) Lie algebra. We also address the fundamental concepts of quantum nondemolition measurements, quantum decoherence and, particularly, quantum entanglement providing for the latter a systematic view on its historical development and mathematical description in multipartite systems. We conclude our review by introducing some of the ubiquitous quantum quantifiers required to measure degrees of quantum entanglement and quantum coherence, deriving the ppp-norm quantum coherence measure for a 1-qubit state.
Quantum information science (QIS) is an interdisciplinary field that explores the principles and applications of quantum mechanics in information processing, communication and computation. QIS leverages the unique properties of quantum systems such as entanglement and superposition to develop new ways of encoding, transmitting and manipulating information. Eventhough quantum technologies hold enormous promises for quantum processing or quantum communication, their potential is still limited by the ability to transmit quantum information and control quantum systems with high precision. Distributing entanglement over large distances holds vast potential for communication applications. However, the inherent fragility of entangled states presents a significant challenge in their distribution. In Part I of this thesis, we investigate the distribution of entanglement over noisy channels. Concerning bipartite entanglement, we introduce novel hardware-agnostic protocols and tools for various tasks that are relevant for reliable quantum communication in the context of quantum computing, including entanglement purification, entanglement verification and fidelity witnessing. Our protocols rely on auxiliary high-dimensional entangled systems to gather non-local information and on new approaches that use but do not consume all available resources. These new tools enhance the performance of our protocols compared to previous strategies, working particularly well for the verification of entangled states where without using auxiliary resources an exponential improvement even with ``optimal'' strategies is obtained. We also investigate the distribution of tripartite entanglement. On the one hand, we extend our protocols to operate with GHZ states, and on the other hand, we develop a new entanglement swapping protocol and enhance the only known entanglement purification protocol for W states. These two strategies collectively enable us to introduce the first quantum repeater for W states. In Part II of the thesis, we explore quantum processing architectures based on logically encoded systems. We investigate many-body systems subject to non-tunable distant-dependent interactions. We demonstrate how using logical encodings we can execute multiqubit non-local gates in a controlled manner solely using local control. This method presents different functionalities which can be exploited for various applications. (1) Efficient way to control the interaction topology of the system, which we use for quantum control where we show how a logical system can be used to control another system by mediating non-local interactions. Based on this functionality, we also develop a quantum simulator with enhanced performance compared to prior methodologies. (2) Interactions resilient against position fluctuations of the system. We demonstrate a significant enhancement in entangling gate fidelities in different systems subjected to thermal noise. (3) Amplification of interactions. We exploit this capability to design a modular quantum computing architecture, which uses multipartite entanglement to implement different intermodular gates.
Within the unified framework of exploiting the relative entropy as a distance measure of quantum correlations, we make explicit the hierarchical structure of quantum coherence, quantum discord, and quantum entanglement in multipartite systems. On this basis, we define a basis-independent measure of quantum coherence and prove that it is exactly equivalent to quantum discord. Furthermore, since the original relative entropy of coherence is a basis-dependent quantity, we investigate the local and nonlocal unitary creation of quantum coherence, focusing on the two-qubit unitary gates. Intriguingly, our results demonstrate that nonlocal unitary gates do not necessarily outperform the local unitary gates. Finally, the additivity relationship of quantum coherence in tripartite systems is discussed in detail, where the strong subadditivity of von Neumann entropy plays an essential role.
The aim of this thesis is to investigate quantum entanglement and quantum nonlocality of bipartite finite-dimensional systems (bipartite qudits). Entanglement is one of the most fascinating non-classical features of quantum theory, and besides its impact on our view of the world, it can be exploited for applications such as quantum cryptography and quantum computing. (...) Although entanglement and nonlocality are ordinarily regarded as one and the same, under close consideration this cannot be taken for granted. The reason for this is that entanglement is defined by the mathematical structure of a quantum state in a composite Hilbert space, whereas nonlocality signifies that the statistical behaviour of a system cannot be described by a local realistic theory. For the latter it is essential that the correlation probabilities of such theories obey so-called Bell inequalities, which are violated for certain quantum states. The main focus of this thesis is on the comparison of both properties with the objective of understanding their relation. (...) Because of the fact that the correlation probabilities in general depend on the measurement settings it is necessary to optimise these in order to reveal nonlocality. This problem is solved for a particular Bell inequality (CGMLP) by means of a self-developed numerical search algorithm. The method is then applied to density matrices of a subspace spanned by the projectors of maximally entangled two-qudit states. This set of states (...) serves to visualise and analyse the state space geometrically.