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arXiv:1004.1944 · Physica Scripta

Convex ordering and quantification of quantumness

Jan Sperling, W Vogel

Published Jun 1, 2015• 74 citations
arXivHTMLPDF

Abstract

The characterization of physical systems requires a comprehensive understanding of quantum effects. One aspect is a proper quantification of the strength of such quantum phenomena. Here, a general convex ordering of quantum states will be introduced which is based on the algebraic definition of classical states. This definition resolves the ambiguity of the quantumness quantification using topological distance measures. Classical operations on quantum states will be considered to further generalize the ordering prescription. Our technique can be used for a natural and unambiguous quantification of general quantum properties whose classical reference has a convex structure. We apply this method to typical scenarios in quantum optics and quantum information theory to study measures which are based on the fundamental quantum superposition principle.

DOI
10.1088/0031-8949/90/7/074024

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The characterization of physical systems requires a comprehensive understanding of quantum effects. One aspect is a proper quantification of the strength of such quantum phenomena. Here, a general convex ordering of quantum states will be introduced which is based on the algebraic definition of classical states. This definition resolves the ambiguity of the quantumness quantification using topological distance measures. Classical operations on quantum states will be considered to further generalize the ordering prescription. Our technique can be used for a natural and unambiguous quantification of general quantum properties whose classical reference has a convex structure. We apply this method to typical scenarios in quantum optics and quantum information theory to study measures which are based on the fundamental quantum superposition principle.
Convex operational theories form a class of physical theories that are built on the operational mixing of states of the system resulting in convex state spaces. Following the operational approach to describe physical experiments, the other operational concepts, such as measurements and state transformations, rise from the properties of the state space. In addition to quantum theory, the convex operational theories include but are not restricted to classical theories and quantum theory of processes. In the light of recent deep interest in quantum information theory, convex operational theories serve as means to consider information-theoretic principles in a more abstract framework. This allows to compare different types of theories against each other and further study the nature of these principles. Some of these principles can then even be used for different axiomatizations of quantum theory. This thesis serves to introduce the mathematical concepts related to convex operational theories and then use them to construct this class of theories in the ordered vector space formalism. We use the constructed class of theories to consider the most important aspects of the theories with applications in physical theories such as quantum theory. We study some of the most important non-classical properties of quantum theory in the more abstract framework of convex operational theories including original research on one of these features.
Various physical phenomena have found use as resources in quantum information processing tasks, and the study of their properties is necessary to provide optimal methods to harness their power. The thesis presents a series of results aiming to characterise the quantitative and operational aspects of general quantum resources, and in particular to establish methods applicable to a variety of resources and emphasise the similarities in their characterisation. Our approach relies on the underlying convex structure of quantum resource theories, employing techniques from convex analysis and optimisation to gain a better understanding of both the fundamental properties of quantum resources as well as our ability to manipulate them efficiently in information processing protocols such as resource distillation. The first part of the thesis introduces a unified framework for resource quantification, establishing general properties of arbitrary convex quantum resource theories and providing insight into the common structure of many physically relevant resources. The second part of the thesis deals with the convex optimisation problems involved in the operational characterisation of two representative quantum resources, quantum entanglement and quantum coherence, where we in particular establish a detailed description of their distillation under several classes of operations, and introduce methods for the interconversion between the two resources. In the final part, we employ geometric methods to characterise the quantification of entanglement measures based on polynomial invariants and apply the results to investigate the monogamy properties of multipartite entanglement.
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Convex operational theories form a class of physical theories that are built on the operational mixing of states of the system resulting in convex state spaces. Following the operational approach to describe physical experiments, the other operational concepts, such as measurements and state transformations, rise from the properties of the state space. In addition to quantum theory, the convex operational theories include but are not restricted to classical theories and quantum theory of processes. In the light of recent deep interest in quantum information theory, convex operational theories serve as means to consider information-theoretic principles in a more abstract framework. This allows to compare different types of theories against each other and further study the nature of these principles. Some of these principles can then even be used for different axiomatizations of quantum theory. This thesis serves to introduce the mathematical concepts related to convex operational theories and then use them to construct this class of theories in the ordered vector space formalism. We use the constructed class of theories to consider the most important aspects of the theories with applications in physical theories such as quantum theory. We study some of the most important non-classical properties of quantum theory in the more abstract framework of convex operational theories including original research on one of these features.
The algebraic quantification of nonclassicality, which naturally arises from the quantum superposition principle, is related to properties of regular nonclassicality quasiprobabilities. The latter are obtained by non-Gaussian filtering of the Glauber-Sudarshan PPP function. They yield lower bounds for the degree of nonclassicality. We also derive bounds for convex combinations of Gaussian states for certifying quantum non-Gaussianity directly from the experimentally accessible nonclassicality quasiprobabilities. Other quantum-state representations, such as sss-parametrized quasiprobabilities, insufficiently indicate or even fail to directly uncover detailed information on the properties of quantum states. As an example, our approach is applied to multi-photon-added squeezed vacuum states.
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