245 research outputs found

    Sudden Death of Entanglement: Classical Noise Effects

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    When a composite quantum state interacts with its surroundings, both quantum coherence of individual particles and quantum entanglement will decay. We have shown that under vacuum noise, i.e., during spontaneous emission, two-qubit entanglement may terminate abruptly in a finite time [T. Yu and J. H. Eberly, \prl {93}, 140404 (2004)], a phenomenon termed entanglement sudden death (ESD). An open issue is the behavior of mixed-state entanglement under the influence of classical noise. In this paper we investigate entanglement sudden death as it arises from the influence of classical phase noise on two qubits that are initially entangled but have no further mutual interaction.Comment: 5 pages, 1 figur

    Enhancement of Rabi Splitting in a Microcavity with an Embedded Superlattice

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    We have observed a large coupling between the excitonic and photonic modes of an AlAs/AlGaAs microcavity filled with an 84-({\rm {\AA}})/20({\rm {\AA}}) GaAs/AlGaAs superlattice. Reflectivity measurements on the coupled cavity-superlattice system in the presence of a moderate electric field yielded a Rabi splitting of 9.5 meV at T = 238 K. This splitting is almost 50% larger than that found in comparable microcavities with quantum wells placed at the antinodes only. We explain the enhancement by the larger density of optical absorbers in the superlattice, combined with the quasi-two-dimensional binding energy of field-localized excitons.Comment: 5 pages, 4 figures, submitted to PR

    A global systematic scoping review of studies analysing indicators, development, and content of national-level physical activity and sedentary behaviour policies

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    Background: National policy approaches to physical activity (PA) promotion and sedentary behaviour (SB) reduction are needed to address rising rates of non-communicable diseases. Understanding the policy process and impact through robust research and evaluation is crucial for facilitating successful reforms in national health policy. This scoping review, therefore, aimed to map the evidence on indicators, development, and content of national PA and/or SB policies globally. Methods: A systematic search of academic and grey literature was conducted through six bibliographic databases, Google, and websites of three large organisations for PA promotion. Results: Out of 24,872 screened documents, 203 publications from 163 studies were selected. The selected studies investigated PA/SB policies in 168 countries worldwide, and we provided summary results for each of the countries. Overall, 69, 29, and 2% of the analyses of national PA/SB policies were conducted for high-, middle-, and low-income countries, respectively. Twenty-two percent of the studies mentioned SB policies as part of their analysis, with only one study focusing solely on assessing SB policies. Operational definitions of policy were found in only 13% of publications. Only 15% of the studies used a conceptual or theoretical framework. A large variety of methods were used for data collection and analysis of PA/SB policy. Conclusions: We found that PA policy research is much more developed than it was considered several years ago. Research around SB policies is still in its infancy, but it seems to have experienced some positive progress in the last few years. Three key issues were identified that should be addressed in further research: [i] there is a lack of PA/SB policy research in low- and middle-income countries, which is an important limitation of the current body of evidence; [ii] the definition of policy varied significantly across studies, and most studies did not rely on any theoretical framework, which may impede cross-study comparisons; and [iii] studies have used a variety of methods to analyse policy, which may also cause problems with comparability. Future PA/SB policy research should aim towards a clearer conceptualisation of policy, greater reliance on existing theoretical frameworks, and the use and further development of standardised methods for PA/SB policy analysis

    Does Treewidth Help in Modal Satisfiability?

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    Many tractable algorithms for solving the Constraint Satisfaction Problem (CSP) have been developed using the notion of the treewidth of some graph derived from the input CSP instance. In particular, the incidence graph of the CSP instance is one such graph. We introduce the notion of an incidence graph for modal logic formulae in a certain normal form. We investigate the parameterized complexity of modal satisfiability with the modal depth of the formula and the treewidth of the incidence graph as parameters. For various combinations of Euclidean, reflexive, symmetric and transitive models, we show either that modal satisfiability is FPT, or that it is W[1]-hard. In particular, modal satisfiability in general models is FPT, while it is W[1]-hard in transitive models. As might be expected, modal satisfiability in transitive and Euclidean models is FPT.Comment: Full version of the paper appearing in MFCS 2010. Change from v1: improved section 5 to avoid exponential blow-up in formula siz

    The complications of ‘hiring a hubby’: gender relations and the commoditisation of home maintenance in New Zealand

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    This paper examines the commoditization of traditionally male domestic tasks through interviews with handymen who own franchises in the company ‘Hire a Hubby’ in New Zealand and homeowners who have paid for home repair tasks to be done. Discussions of the commoditization of traditionally female tasks in the home have revealed the emotional conflicts of paying others to care as well as the exploitative and degrading conditions that often arise when work takes place behind closed doors. By examining the working conditions and relationships involved when traditionally male tasks are paid for, this paper raises important questions about the valuing of reproductive labour and the production of gendered identities. The paper argues that while working conditions and rates of pay for ‘hubbies’ are better than those for people undertaking commoditized forms of traditionally female domestic labour, the negotiation of this work is still complex and implicated in gendered relations and identities. Working on the home was described by interviewees as an expression of care for family and a performance of the ‘right’ way to be a ‘Kiwi bloke’ and a father. Paying others to do this labour can imply a failure in a duty of care and in the performance of masculinity
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