3,230 research outputs found
Demonstration of efficient scheme for generation of "Event Ready" entangled photon pairs from single photon source
We present a feasible and efficient scheme, and its proof-of-principle
demonstration, of creating entangled photon pairs in an event-ready way using
only simple linear optical elements and single photons. The quality of
entangled photon pair produced in our experiment is confirmed by a strict
violation of Bell's inequality. This scheme and the associated experimental
techniques present an important step toward linear optics quantum computation.Comment: 4 pages, 4 figure
Smallest disentangling state spaces for general entangled bipartite quantum states
PACS numbers: 03.67.-a, 03.65.-w, 03.65.Ta, 03.65.Ud.Entangled quantum states can be given a separable decomposition if we relax the restriction that the local operators be quantum states. Motivated by the construction of classical simulations and local hidden variable models, we construct `smallest' local sets of operators that achieve this. In other words, given an arbitrary bipartite quantum state we construct convex sets of local operators that allow for a separable decomposition, but that cannot be made smaller while continuing to do so. We then consider two further variants of the problem where the local state spaces are required to contain the local quantum states, and obtain solutions for a variety of cases including a region of pure states around the maximally entangled state. The methods involve calculating certain forms of cross norm. Two of the variants of the problem have a strong relationship to theorems on ensemble decompositions of positive operators, and our results thereby give those theorems an added interpretation. The results generalise those obtained in our previous work on this topic [New J. Phys. 17, 093047 (2015)].EP/K022512/1/Engineering and Physical Sciences Research Counci
Characterizing entanglement with geometric entanglement witnesses
We show how to detect entangled, bound entangled, and separable bipartite
quantum states of arbitrary dimension and mixedness using geometric
entanglement witnesses. These witnesses are constructed using properties of the
Hilbert-Schmidt geometry and can be shifted along parameterized lines. The
involved conditions are simplified using Bloch decompositions of operators and
states. As an example we determine the three different types of states for a
family of two-qutrit states that is part of the "magic simplex", i.e. the set
of Bell-state mixtures of arbitrary dimension.Comment: 19 pages, 4 figures, some typos and notational errors corrected. To
be published in J. Phys. A: Math. Theo
Qubit-portraits of qudit states and quantum correlations
The machinery of qubit-portraits of qudit states, recently presented, is
consider here in more details in order to characterize the presence of quantum
correlations in bipartite qudit states. In the tomographic representation of
quantum mechanics, Bell-like inequalities are interpreted as peculiar
properties of a family of classical joint probability distributions which
describe the quantum state of two qudits. By means of the qubit-portraits
machinery a semigroup of stochastic matrices can be associated to a given
quantum state. The violation of the CHSH inequalities is discussed in this
framework with some examples, we found that quantum correlations in qutrit
isotropic states can be detected by the suggested method while it cannot in the
case of qutrit Werner states.Comment: 12 pages, 4 figure
Entanglement Measures with Asymptotic Weak-Monotonicity as Lower (Upper) Bound for the Entanglement of Cost (Distillation)
We propose entanglement measures with asymptotic weak-monotonicity. We show
that a normalized form of entanglement measures with the asymptotic
weak-monotonicity are lower (upper) bound for the entanglement of cost
(distillation).Comment: 3 pages, RevTe
Hermitian Tensor Product Approximation of Complex Matrices and Separability
The approximation of matrices to the sum of tensor products of Hermitian
matrices is studied. A minimum decomposition of matrices on tensor space
in terms of the sum of tensor products of Hermitian matrices
on and is presented. From this construction the separability of
quantum states is discussed.Comment: 16 page
Bounds for multipartite concurrence
We study the entanglement of a multipartite quantum state. An inequality
between the bipartite concurrence and the multipartite concurrence is obtained.
More effective lower and upper bounds of the multipartite concurrence are
obtained. By using the lower bound, the entanglement of more multipartite
states are detected.Comment: 8 page
Test for entanglement using physically observable witness operators and positive maps
Motivated by the Peres-Horodecki criterion and the realignment criterion we
develop a more powerful method to identify entangled states for any bipartite
system through a universal construction of the witness operator. The method
also gives a new family of positive but non-completely positive maps of
arbitrary high dimensions which provide a much better test than the witness
operators themselves. Moreover, we find there are two types of positive maps
that can detect 2xN and 4xN bound entangled states. Since entanglement
witnesses are physical observables and may be measured locally our construction
could be of great significance for future experiments.Comment: 6 pages, 1 figure, revtex4 styl
A mathematical model for fibro-proliferative wound healing disorders
The normal process of dermal wound healing fails in some cases, due to fibro-proliferative disorders such as keloid and hypertrophic scars. These types of abnormal healing may be regarded as pathologically excessive responses to wounding in terms of fibroblastic cell profiles and their inflammatory growth-factor mediators. Biologically, these conditions are poorly understood and current medical treatments are thus unreliable.
In this paper, the authors apply an existing deterministic mathematical model for fibroplasia and wound contraction in adult mammalian dermis (Olsenet al., J. theor. Biol. 177, 113–128, 1995) to investigate key clinical problems concerning these healing disorders. A caricature model is proposed which retains the fundamental cellular and chemical components of the full model, in order to analyse the spatiotemporal dynamics of the initiation, progression, cessation and regression of fibro-contractive diseases in relation to normal healing. This model accounts for fibroblastic cell migration, proliferation and death and growth-factor diffusion, production by cells and tissue removal/decay.
Explicit results are obtained in terms of the model processes and parameters. The rate of cellular production of the chemical is shown to be critical to the development of a stable pathological state. Further, cessation and/or regression of the disease depend on appropriate spatiotemporally varying forms for this production rate, which can be understood in terms of the bistability of the normal dermal and pathological steady states—a central property of the model, which is evident from stability and bifurcation analyses.
The work predicts novel, biologically realistic and testable pathogenic and control mechanisms, the understanding of which will lead toward more effective strategies for clinical therapy of fibro-proliferative disorders
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