140,280 research outputs found

    Characterization and quantification of symmetric Gaussian state entanglement through a local classicality criterion

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    A necessary and sufficient condition for characterization and quantification of entanglement of any bipartite Gaussian state belonging to a special symmetry class is given in terms of classicality measures of one-party states. For Gaussian states whose local covariance matrices have equal determinants it is shown that separability of a two-party state and classicality of one party state are completely equivalent to each other under a nonlocal operation, allowing entanglement features to be understood in terms of any available classicality measure.Comment: 5 pages, 1 figure. Replaced with final published versio

    Detecting Cognitive Load during Working Memory Tasks utilizing a Digitizer Tablet

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    The purpose of this line of research is to determine whether the ‘Digitizer’ is a reliable and valid way to measure cognitive load during dual working memory-drawing tasks. A quasi-experimental study was conducted at the University of Arkansas in a research laboratory, and participants included seven right-handed healthy adults with normal or corrected vision and no reading difficulty. The participants were selected on a volunteer basis. The study required participants to draw circles while continuously performing in three conditions – one baseline and two working memory experimental tasks, administered in counterbalanced order. The baseline task was to read an 8th grade level passage at comfortable speed and loudness level. The working memory tasks were symmetry span and operation span tasks. The operation span task required the participants to remember letters in sequence while simultaneously verifying arithmetic operations presented after each letter. The symmetry span task required participants to remember the position of the highlighted square in a grid in sequence while simultaneously determining the symmetricity of a figure presented afterwards. Both tasks were completed while drawing continuous circles on the ‘Digitizer’. A separate repeated measures analysis of variance (ANOVA) was conducted for each measure. A significant omnibus effect was found for the stroke duration measure only. Post-hoc paired tests showed that baseline was higher (p=.01) in stroke duration than in operation span task and symmetry span task. In this literature review, the results and elements of the study are described in full to inform future research. It was initially assumed that the working memory load would be significantly less in the baseline task as compared to the two working memory tasks; however, the data alternatively indicated that it taxed working memory more. With reading comprehension as a reference condition, it is logical to conclude that there is evidence of cognitive load in working memory tasks as measured by manual disfluencies. This literature review outlines potential adaptations and highlights primary weaknesses for future study in this area

    How to quantify coherence: Distinguishing speakable and unspeakable notions

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    Quantum coherence is a critical resource for many operational tasks. Understanding how to quantify and manipulate it also promises to have applications for a diverse set of problems in theoretical physics. For certain applications, however, one requires coherence between the eigenspaces of specific physical observables, such as energy, angular momentum, or photon number, and it makes a difference which eigenspaces appear in the superposition. For others, there is a preferred set of subspaces relative to which coherence is deemed a resource, but it is irrelevant which of the subspaces appear in the superposition. We term these two types of coherence unspeakable and speakable respectively. We argue that a useful approach to quantifying and characterizing unspeakable coherence is provided by the resource theory of asymmetry when the symmetry group is a group of translations, and we translate a number of prior results on asymmetry into the language of coherence. We also highlight some of the applications of this approach, for instance, in the context of quantum metrology, quantum speed limits, quantum thermodynamics, and NMR. The question of how best to treat speakable coherence as a resource is also considered. We review a popular approach in terms of operations that preserve the set of incoherent states, propose an alternative approach in terms of operations that are covariant under dephasing, and we outline the challenge of providing a physical justification for either approach. Finally, we note some mathematical connections that hold among the different approaches to quantifying coherence.Comment: A non-technical summary of the results and applications is provided in the first section. V5 close to the published version. Typos correcte

    Interplay between nonclassicality and PT\mathcal{PT} symmetry in an effective two level system with open system effects

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    A three level atom in Λ\Lambda configuration is reduced to an effective two level system, under appropriate conditions, and its PT\mathcal{PT} symmetric properties are investigated. This effective qubit system when subjected to a beam-splitter type of interaction, it provides the scope of directly (indirectly) probing the nonclassical properties of the output (input) state. Here, we study nonclassical properties of the output state by using some well known measures of nonclassical correlations like the measurement induced disturbance, concurrence and negativity. The nonclassical features are found to enhance in the PT\mathcal{PT} symmetric (PTS) phase compared to the PT\mathcal{PT} symmetry broken (PTSB) phase. Further, the output ports of the beam-splitter are subjected to different quantum noise channels, both non-Markovian, e.g., random telegraph noise as well as Markovian, e.g., phase damping, and amplitude damping noise. The application of noise channels is found to decrease the degree of nonclassicality, though continuing to exhibit distinct behavior in PTS and PTSB phases, with the dominant behavior appearing in the former case

    Chirality in Liquid Crystals: from Microscopic Origins to Macroscopic Structure

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    Molecular chirality leads to a wonderful variety of equilibrium structures, from the simple cholesteric phase to the twist-grain-boundary phases, and it is responsible for interesting and technologically important materials like ferroelectric liquid crystals. This paper will review some recent advances in our understanding of the connection between the chiral geometry of individual molecules and the important phenomenological parameters that determine macroscopic chiral structure. It will then consider chiral structure in columnar systems and propose a new equilibrium phase consisting of a regular lattice of twisted ropes.Comment: 20 pages with 6 epsf figure

    Groupoids: unifying internal and external symmetry

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    The aim of this paper is to explain, mostly through examples, what groupoids are and how they describe symmetry. We will begin with elementary examples, with discrete symmetry, and end with examples in the differentiable setting which involve Lie groupoids and their corresponding infinitesimal objects, Lie algebroids.Comment: 18 page

    Purification-based metric to measure the distance between quantum states and processes

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    In this work we study the properties of an purification-based entropic metric for measuring the distance between both quantum states and quantum processes. This metric is defined as the square root of the entropy of the average of two purifications of mixed quantum states which maximize the overlap between the purified states. We analyze this metric and show that it satisfies many appealing properties, which suggest this metric is an interesting proposal for theoretical and experimental applications of quantum information.Comment: 11 pages, 2 figures. arXiv admin note: text overlap with arXiv:quant-ph/0408063, arXiv:1107.1732 by other author

    Quantum dynamics as a physical resource

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    How useful is a quantum dynamical operation for quantum information processing? Motivated by this question we investigate several strength measures quantifying the resources intrinsic to a quantum operation. We develop a general theory of such strength measures, based on axiomatic considerations independent of state-based resources. The power of this theory is demonstrated with applications to quantum communication complexity, quantum computational complexity, and entanglement generation by unitary operations.Comment: 19 pages, shortened by 3 pages, mainly cosmetic change
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