다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Annals of physics

One of the best signatures of nonclassicality in a quantum system is the existence of correlations that have no classical counterpart. Different methods for quantifying the quantum and classical parts of correlations are among the more actively studied topics of quantum-information theory over the past decade. Entanglement is the most prominent of these correlations, but in many cases unentangled states exhibit nonclassical behavior too. Thus distinguishing quantum correlations other than entanglement provides a better division between the quantum and classical worlds, especially when considering mixed states. Here different notions of classical and quantum correlations quantified by quantum discord and other related measures are reviewed. In the first half, the mathematical properties of the measures of quantum correlations are reviewed, related to each other, and the classical-quantum division that is common among them is discussed. In the second half, it is shown that the measures identify and quantify the deviation from classicality in various quantum-information-processing tasks, quantum thermodynamics, open-system dynamics, and many-body physics. It is shown that in many cases quantum correlations indicate an advantage of quantum methods over classical ones.

/pdf/the-classical-quantum-boundary-for-correlations-discord-and-3rixt19msw.pdf

The classical-quantum boundary for correlations: Discord and related measures

a ) p. 131 The discussion between eqs. (5.14) and (5.15) is incorrect (dA should be made as large as possible!). b ) p. 256 In the figure, the numbers 6) and 7) occur twice. c ) p. 292 At the end of section 12.5, it should be the space of isospectral 0Hermitian matrices. d ) p. 306 A ”Tr” is missing in eq. (13.43). e ) p. 327, Eq. (14.64b) is 〈Trρ〉B = N(14N+10) (5N+1)(N+3) should be 〈Trρ〉B = 8N+7 (N+2)(N+4)

Geometry of Quantum States: Frontmatter

Quantum theory: Concepts and methods

We study a quantum state transfer between two qubits interacting with the ends of a quantum wire consisting of linearly arranged spins coupled by an excitation conserving, time-independent Hamiltonian. We show that, if we control the coupling between the source and the destination qubits and the ends of the wire, the evolution of the system can lead to an almost perfect transfer even in the case in which all nearest-neighbour couplings between the internal spins of the wire are equal.

Unmodulated spin chains as universal quantum wires

We analyze quantum network primitives which are entanglement breaking We show superadditivity of quantum and classical capacity regions for quantum multiple-access channels and the quantum butterfly network Since the effects are especially visible at high noise they suggest that quantum information effects may be particularly helpful in the case of the networks with occasional high noise rates The present effects provide a qualitative borderline between superadditivities of bipartite and multipartite systems

Nonadditivity of quantum and classical capacities for entanglement breaking multiple-access channels and the butterfly network

We observe that changing a phase at a single point in a discrete quantum walk results in a rather surprising localization effect. For certain values of this phase change the possibility of localization strongly depends on the internal coin state of the walker.

Trapping a particle of a quantum walk on the line

Contextuality is central to both the foundations of quantum theory and to the novel information processing tasks Although it was recognized before Bell's nonlocality, despite some recent proposals, it still faces a fundamental problem: how to quantify its presence? In this work, we provide a framework for quantifying contextuality We conduct two complementary approaches: (i) bottom-up approach, where we introduce a communication game, which grasps the phenomenon of contextuality in a quantitative manner; (ii) top-down approach, where we just postulate two measures - relative entropy of contextuality and contextuality cost, analogous to existent measures of non-locality (a special case of contextuality) We then match the two approaches, by showing that the measure emerging from communication scenario turns out to be equal to the relative entropy of contextuality We give analytical formulas for the proposed measures for some contextual systems Furthermore we explore properties of these measures such as monotonicity or additivity

Quantifying Contextuality

We study the ordering of two-qubit states with respect to the degree of bipartite entanglement using the Wootters concurrence - a measure of the entanglement of formation - and the negativity - a measure of the entanglement cost under the positive-partial-transpose-preserving operations. For two-qubit pure states, the negativity is the same as the concurrence. However, we demonstrate analytically on simple examples of various mixtures of Bell and separable states that the entanglement measures can impose different orderings on the states. We show which states, in general, give the maximally different predictions (i) when one of the states has the concurrence greater but the negativity smaller than those for the other state and (ii) when the states are entangled to the same degree according to one of the measures, but differently according to the other.

/pdf/ordering-two-qubit-states-with-concurrence-and-negativity-1gwp5syv9i.pdf

Andrzej Grudka

Papers

Unmodulated spin chains as universal quantum wires

Nonadditivity of quantum and classical capacities for entanglement breaking multiple-access channels and the butterfly network

Trapping a particle of a quantum walk on the line

Quantifying Contextuality

Ordering two-qubit states with concurrence and negativity