Showing papers on "Concurrence published in 2008"

Universal observable detecting all two-qubit entanglement and determinant based separability tests

Abstract: We construct a single observable measurement of which mean value on four copies of an {\it unknown} two-qubit state is sufficient for unambiguous decision whether the state is separable or entangled. In other words, there exists a universal collective entanglement witness detecting all two-qubit entanglement. The test is directly linked to a function which characterizes to some extent the entanglement quantitatively. This function is an entanglement monotone under so--called local pure operations and classical communication (pLOCC) which preserve local dimensions. Moreover it provides tight upper and lower bounds for negativity and concurrence. Elementary quantum computing device estimating unknown two-qubit entanglement is designed.

Proper monogamy inequality for arbitrary pure quantum states

Abstract: We provide a detailed proof of an analytical lower bound of entanglement quantified by concurrence for arbitrary bipartite quantum states. It is shown that though the bound does not allow one to detect bound entanglement, it is tight for some mixed states and can detect most of the free entanglement. On the other hand, it is known that the entanglement monogamy inequality proposed by Coffman, Kundu, and Wootters is, in general, not true for higher-dimensional quantum states. Inducing from the lower bound of concurrence, we find a proper form of entanglement monogamy inequality for arbitrary pure quantum states.

Lower bounds on entanglement measures from incomplete information

Abstract: How can we quantify the entanglement in a quantum state, if only the expectation value of a single observable is given? This question is of great interest for the analysis of entanglement in experiments, since in many multiparticle experiments the state is not completely known. We present several results concerning this problem by considering the estimation of entanglement measures via Legendre transforms. First, we present a simple algorithm for the estimation of the concurrence and extensions thereof. Second, we derive an analytical approach to estimate the geometric measure of entanglement, if the diagonal elements of the quantum state in a certain basis are known. Finally, we compare our bounds with exact values and other estimation methods for entanglement measures.

Entangled quantum heat engines based on two two-spin systems with Dzyaloshinski-Moriya anisotropic antisymmetric interaction

Abstract: We construct an entangled quantum heat engine (EQHE) based on two two-spin systems with Dzyaloshinski-Moriya (DM) anisotropic antisymmetric interaction. By applying the explanations of heat transferred and work performed at the quantum level in Kieu’s work [Phys. Rev. Lett. 93, 140403 (2004)], the basic thermodynamic quantities, i.e., heat transferred, net work done in a cycle and efficiency of EQHE are investigated in terms of DM interaction and concurrence. The validity of the second law of thermodynamics is confirmed in the entangled system. It is found that there is a same efficiency for both antiferromagnetic and ferromagnetic cases, and the efficiency can be controlled in two manners: (1) only by spin-spin interaction J and DM interaction D; (2) only by the temperature T and concurrence C. In order to obtain a positive net work, we need not entangle all qubits in two two-spin systems and we only require the entanglement between qubits in a two-spin system not be zero. As the ratio of entanglement between qubits in two two-spin systems increases, the efficiency will approach infinitely the classical Carnot one. An interesting phenomenon is an abrupt transition of the efficiency when the entanglements between qubits in two two-spin systems are equal.

Multipartite entanglement measure for all discrete systems

Abstract: Via a multidimensional complementarity relation we derive an operational entanglement measure for any discrete quantum system, i.e., for any multidimensional and multipartite system. This measure admits a separation into different classes of entanglement obtained by using a flip operator $2,3,\dots{},n$ times, defining a $m$-flip concurrence. This operator sum has the practical feature to allow one to calculate for mixed states bounds on this $m$-flip concurrence. Moreover, the information content of an $n$-partite multidimensional system admits a simple and intuitive interpretation in terms of single particle obtainable information, entanglement, and information due to lack of classical knowledge of the quantum state under investigation. Explicitly, the three qubit system is analyzed and, e.g., the physical difference in entanglement of the W state, the Greenberger-Horne-Zeilinger (GHZ) state, or a biseparable state is revealed.

Estimation of concurrence for multipartite mixed states

Abstract: We investigate the lower bound of concurrence for multipartite quantum mixed states. Analytical lower bounds are derived for some multipartite systems, by establishing functional relations between concurrence and the generalized partial transpositions.

Proposal for direct measurement of concurrence via visibility in a cavity QED system

Abstract: An experimental scheme is proposed that allows direct measurement of the concurrence of a two-qubit cavity system. It is based on the cavity-QED technology using atoms as flying qubits and relies on the identity of the two-particle visibility of the atomic probability with the concurrence of the cavity system. The scheme works for any arbitrary pure initial state of the two-qubit cavity system.

Entanglement of formation and concurrence for mixed states

Abstract: We review some results on analytical computations of the measures for quantum entanglement: entanglement of formation and concurrence. We introduce some estimations of the lower bounds for the entanglement of formation in bipartite mixed states, and of lower bounds for the concurrence in bipartite and tripartite systems. The results on lower bounds for the concurrence are also generalized to arbitrary multipartite systems.

Evolution of entanglement for quantum mixed states

Abstract: A simple relation is introduced for concurrence to describe how much the entanglement of a bipartite system is at least left if either (or both) subsystem undergoes an arbitrary physical process. This provides a lower bound for concurrence of mixed states (pure states are included) in contrast to the upper bound given by Konrad et al. [Nat. Phys. 4, 99 (2008)]. Our results are also suitable for general high-dimensional bipartite quantum systems.

Descriptor and Folksonomy Concurrence in Education Related Scholarly Research.

Abstract: Folksonomies are a decentralized yet collaborative form of classification based on user-defined keywords (also known as tags). Although this uncontrolled method of classification lacks rules for term standardization and usage, it has potential for organizational patterns and an emerging vocabulary (terminology). The objective of this research is to analyze the descriptors and tags from journal articles indexed in the Education Resources Information Center (ERIC) and the folksonomy-based website CiteULike to determine overlap between the controlled and uncontrolled vocabularies. Metadata from 2,786 journal articles indexed in ERIC and CiteULike was collected using Perl and MySQL. The total metadata was comprised of 2,899 unique ERIC descriptors, 3,176 unique CiteULike tags, and 1,083 unique CiteULike users. An analysis of this metadata revealed that 240 of the CiteULike tags matched ERIC descriptors. The low number of tag-descriptor matches in this research indicates that CiteULike users do not use the same terminology as subject specialists who maintain descriptors in the ERIC thesaurus.

A Family of Concurrence Monotones and its Applications

Abstract: We extend the definition of concurrence into a family of entanglement monotones, which we call concurrence monotones. We discuss their properties and advantages as computational manageable measures of entanglement, and show that for pure bipartite states all measures of entanglement can be written as functions of the concurrence monotones. We then show that the concurrence monotones provide bounds on quantum information tasks. As an example, we discuss their applications to remote entanglement distributions (RED) such as entanglement swapping and remote preparation of bipartite entangled states (RPBES). We prove a powerful theorem which states what kind of (possibly mixed) bipartite states or distributions of bipartite states can not be remotely prepared. The theorem establishes an upper bound on the amount of G-concurrence (one member in the concurrence family) that can be created between two single-qudit nodes of quantum networks by means of tripartite RED. For pure bipartite states the bound on the G-concurrence can always be saturated by RPBES.

Concurrence vectors for entanglement of high-dimensional systems

Abstract: The concurrence vectors are proposed by employing the fundamental representation of An Lie algebra, which provides a clear criterion to evaluate the entanglement of bipartite systems of arbitrary dimension. Accordingly, a state is separable if the norm of its concurrence vector vanishes. The state vectors related to SU(3) states and SO(3) states are discussed in detail. The sign situation of nonzero components of concurrence vectors of entangled bases presents a simple criterion to judge whether the whole Hilbert subspace spanned by those bases is entangled, or there exists an entanglement edge. This is illustrated in terms of the concurrence surfaces of several concrete examples.

Measurable Concurrence of Mixed States

Abstract: We show that bipartite concurrence for rank-2 mixed states of qubits is written by an observable which can be exactly and directly measurable in experiment by local projective measurements, provided that four copies of the composite quantum system are available. In addition, for a tripartite quantum pure state of qubits, the 3-tangle is also shown to be measurable only by projective measurements on the reduced density matrices of a pair of qubits conditioned on four copies of the state.

Statistics of orbital entanglement production in quantum-chaotic dots

Abstract: The production of orbitally entangled electrons in quantum-chaotic dots is investigated from a statistical point of view. The degree of entanglement is quantified through the concurrence and the entanglement of formation. We calculate the complete statistical distributions of the entanglement measures by using random matrix theory. Simple analytical expressions are provided for the concurrence distributions. We identify clear signatures of time-reversal invariance in the production of entanglement at the level of the entanglement-measure distributions, such as the ability of producing maximally entangled (Bell) states, which passed unnoticed in previous works, where only the first two moments of the distributions were studied.

A conceptual framework for analysis of market efficiency

Abstract: Important agricultural marketing policies and decisions are constantly before industry and government. Much market research is being supported. There is a need to “bridge” research with policy. The core of this paper is to develop a conceptual framework that spans the needed analysis of marketing efficiency. The basic point is that marketing policy must focus on both competition and physical operations. The analysis of this paper builds upon Clark's concept of workable competition and Sosnick's extension to the concept of effective competition. Market efficiency is separated into operational efficiency and exchange efficiency components; the determinants of each component are diagnosed and analyzed in terms of costs and pricing. While the agricultural marketing process produces increments of product form, space, and time utility, costs are incurred. Cost analysis is central to the notion of operational efficiency; cost levels depend upon market organization and the feasible set of market logistics. Exchange efficiency refers primarily to price; the effectiveness with which price reflects costs depends upon market structures and the applicable competitive strategies. The conceptual framework developed in this paper integrates the preceding relationships and formalizes an approach for decisions. Trade-offs often exist between operational efficiency and exchange efficiency components of market efficiency. When a trade-off relationship exists, market efficiency is maximized by equalizing the gain in one component with the opportunity-cost loss in the other component. Le gourvernement el I'industrie font continuellemeni face aďimportante decisions dans le domaine des marches el de la politique agricloe. Ces deux groupes subven-tionnenl les recherches dans ce domaine. II y a un besoin de Her la recherche avec la politique. ľessentiel de cet article est de developper un codre qui comprend ľanalyse necessaire pour ľefficacite du marche, le point important est que le politique du marche doit se concentrer sur le concurrence et les operations. L'analyse de cet article travail sur le theorie de concurrence realisable de Clark et sur celle Sosnick traitant de ľExtension de la concurrence effective. ľefficacite du marche est diverse en deux elements: ľexploitation efftcace el ľechange efficace, les facteurs determinant de chaque element sont soumis a un diagnostic et a une analyse en termes du cout et du prix

Bounds on bipartitely shared entanglement reduced from superposed tripartite quantum states

Abstract: For a tripartite pure state superposed by two individual states, the bipartitely shared entanglement can always be achieved by local measurements of the third party. Consider the different aims of the third party, i.e. maximizing or minimizing the bipartitely shared entanglement, we find bounds on both the possible bipartitely shared entanglement of the superposition state in terms of the corresponding entanglement of the two states being superposed. In particular, by choosing the concurrence as bipartite entanglement measure, we obtain calculable bounds for tripartite (2 ⊗ 2 ⊗ n)-dimensional cases.

Agreement: Concurrence of Wills, or Offer and Acceptance?

Abstract: Four questions about agreement, with Article 81 EC, can be distinguished. The first is one of analysis: What is it for something to be an agreement within Article 81? The second is one of linguistic definition: What, for the purposes of Article 81, does “agreement” mean? This differs from the analytical question as it concerns a word in a particular language, but the answers to the two questions will be substantively the same. The third question is epistemic: How can we know whether X and Y have an agreement within Article 81? This can be recast in legal terms as: What, for the purposes of Article 81, is sufficient evidence to prove the existence of an agreement?1 The fourth is a question about conditions: What are the conditions for X and Y to have an agreement within Article 81? The answer to this will depend on the kind of condition at issue; it is plausible to hold for example that, if the question concerns truthor assertability-conditions June 2008 European Competition Journal 103

Entanglement of formation is non-monotonic with concurrence: a simple proof

Abstract: In this paper we explore the non-monotonic nature of entanglement of formation with respect to concurrence for pure bipartite states. For pure bipartite system, one of the basic physical reason of this non-monotonicity character is due to the existence of incomparable states, i.e., the pure bipartite states which are not convertible to each other by LOCC with certainty.

Bounds on Bipartitiely Shared Entanglement Reduced from Superposed Tripartite Quantum States

Abstract: For a tripartite pure state superposed by two individual states, the bipartitely shared entanglement can always be achieved by local measurements of the third party. Consider the different aims of the third party, i.e. maximizing or minimizing the bipartitely shared entanglement, we find bounds on both the possible bipartitely shared entanglement of the superposition state in terms of the corresponding entanglement of the two states being superposed. In particular, by choosing the concurrence as bipartite entanglement measure, we obtain calculable bounds for tripartite $(2\otimes 2\otimes n)$ -dimensional cases.

Proof of a lower bound for bipartite concurrence via equivalence to an observable entanglement measure

Abstract: In this Brief Report, we prove that an analytically solvable two-qubit entanglement monotone introduced by Zhang et al. [Phys. Rev. A 76, 032306 (2007)] is no greater than the square of concurrence. This proof is based on the equivalence between Zhang et al.'s monotone and an observable entanglement measure for mixed states suggested by Mintert and Buchleitner [Phys. Rev. Lett. 98, 140505 (2007)]. Our result may clarify the connections between several recently defined entanglement measures and help understand their possible applications in quantum-information theory.

Formation of three-body entanglement via a vacuum optical cavity induction in Tavis-Cummings model

Abstract: After briefly introducing Akhtarshenas, concurrence vector and subvector for describing many-body entanglement, we investigate the entanglement formation for a system which contains three bodies, i.e. two identical atoms and a single-model cavity field, in the Tavis–Cummings model by calculating the concurrences. The results show that the coupling strength between two atoms, the decay cavity and the atomic spontaneous emission can change the entanglement of formation according to different modes: these factors destroy periodicity and symmetry of all concurrences, and that the coupling strength of two atoms does not change the peak value of concurrence (C), but the strength of decay cavity and the atomic spontaneous emission decline in the peak value of concurrence (C) and the latter is more serious than the former under the same strengths. The concurrence vector and subvector are a useful measure of entanglement for a pure state of the many-body system, in that it can give novel pictures about the entanglements for the entire system and between its inner bodies.

Concurrence of Stochastic 1-Qubit Maps

Abstract: Explicit expressions for the concurrence of all positive and trace-preserving ("stochastic") 1-qubit maps are presented. By a new method we find the relevant convex roof pattern. We conclude that two component optimal decompositions always exist. Our results can be transferred to $2 \times n$-quantum systems providing the concurrence for all rank two density operators as well as a lower bound for their entanglement of formation.

Simple proof for the bounds of concurrence

Abstract: Theoretical Physics Division, Chern Institute of Mathematics, Nankai University, Tianjin, 300071, P.R.China(Dated: August 23, 2008)The bounds of concurrence in [F. Mintert and A. Buchleitner, Phys. Rev. Lett. 98, 140505(2007)] and [C. Zhang et. al., arXiv: 0806.2598] are proved by using two properties of the fidelity.This shows these two concepts in quantum information are closely related.

Entanglement in disordered systems at criticality

Abstract: Entanglement is a physical resource of a quantum system just like mass, charge or energy. Moreover it is an essential tool for many purposes of nowadays quantum information processing, e.g. quantum teleportation, quantum cryptography or quantum computation. In this work we investigate an extended system of N qubits. In our system a qubit is the absence or presence of an electron at a site of a tight-binding system. Several measures of entanglement between a given qubit and the rest of the system and also the entanglement between two qubits and the rest of the system are calculated in a one-electron picture in the presence of disorder. We invoke the power law band random matrix model which even in one dimension is able to produce multifractal states that fluctuate at all length scales. The concurrence, the tangle and the entanglement entropy all show interesting scaling properties. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Entanglement dynamics in quantum spin chains

Abstract: We study patterns of temporal evolution, creation and transport, of entanglement in quantum spin chains. The model used is an isotropic Heisenberg chain with periodic boundary conditions, and we obtain in analytic form the time dependence of concurrence and negativity of various pairs of spins in the system. The objective of the present study is to assess the usefulness of various averaged entanglement measures in the characterization of entangling properties of quantum evolutions.

Entanglement in One-Dimensional Anderson Model with Long-Range Correlated Disorder

Abstract: By using the measure of concurrence, the entanglement of the ground state in the one-dimensional Anderson model is studied with consideration of the long-range correlations. Three kinds of correlations are discussed. We compare the effects of the long-rang Gaussian and power-law correlations between the site energies on the concurrence, and demonstrate the existence of the band structure of the concurrence in the power-law case. The emergence of the sharp kink on the concurrence curve shown in the intraband or in the interband indicates the position at which the localization extent of the state may have the severe variation. We use the Rudin–Shapiro model to describe the site energy distribution of the nucleotides of the DNA chain: guanine (G), adenine (A), cytosine(C), thymine (T). This model is a tetradic quasiperiodic sequence and is shown to be long-range correlated. Our results show that correlations between the site energies increase the concurrences.