7,324 research outputs found

    Coherence-Preserving Quantum Bits

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    Real quantum systems couple to their environment and lose their intrinsic quantum nature through the process known as decoherence. Here we present a method for minimizing decoherence by making it energetically unfavorable. We present a Hamiltonian made up solely of two-body interactions between four two-level systems (qubits) which has a two-fold degenerate ground state. This degenerate ground state has the property that any decoherence process acting on an individual physical qubit must supply energy from the bath to the system. Quantum information can be encoded into the degeneracy of the ground state and such coherence-preserving qubits will then be robust to local decoherence at low bath temperatures. We show how this quantum information can be universally manipulated and indicate how this approach may be applied to a quantum dot quantum computer.Comment: 5 pages, 1 figur

    Weak Gravitational Flexion

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    Flexion is the significant third-order weak gravitational lensing effect responsible for the weakly skewed and arc-like appearance of lensed galaxies. Here we demonstrate how flexion measurements can be used to measure galaxy halo density profiles and large-scale structure on non-linear scales, via galaxy-galaxy lensing, dark matter mapping and cosmic flexion correlation functions. We describe the origin of gravitational flexion, and discuss its four components, two of which are first described here. We also introduce an efficient complex formalism for all orders of lensing distortion. We proceed to examine the flexion predictions for galaxy-galaxy lensing, examining isothermal sphere and Navarro, Frenk & White (NFW) profiles and both circularly symmetric and elliptical cases. We show that in combination with shear we can precisely measure galaxy masses and NFW halo concentrations. We also show how flexion measurements can be used to reconstruct mass maps in 2-D projection on the sky, and in 3-D in combination with redshift data. Finally, we examine the predictions for cosmic flexion, including convergence-flexion cross-correlations, and find that the signal is an effective probe of structure on non-linear scales.Comment: 17 pages, including 12 figures, submitted to MNRA

    Sectoral Changes in the Labour Force over the Period 1961-1980 with Particular Reference to Public Sector and Services Employment. Special Article in Quarterly Economic Commentary, Winter 2015

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    A knowledge of the significant changes which have been taking place in the sectoral composition of employment is fundamental to a proper understanding of the recent evolution of the labour force. This paper traces the changes in the numbers at work in broad sectors of the Irish economy over the period 1961-80. The basic information is given in Appendix I, Table A which contains an annual sectoral subdivision under four broad headings (Agriculture, Manufacturing, Building and Services); Tables 1 and lA following show these data for selected years* in this period with a somewhat more detailed sectoral subdivision, the second table giving absolute and relative employment changes by sector for the 1961/1971 and 1971/1979 periods

    A Tunable Echelle Imager

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    We describe and evaluate a new instrument design called a Tunable Echelle Imager (TEI). In this instrument, the output from an imaging Fabry-Perot interferometer is cross-dispersed by a grism in one direction and dispersed by an echelle grating in the perpendicular direction. This forms a mosaic of different narrow-band images of the same field on a detector. It offers a distinct wavelength multiplex advantage over a traditional imaging Fabry-Perot device. Potential applications of the TEI include spectrophotometric imaging and OH-suppressed imaging by rejection.Comment: 11 pages, 12 figures, accepted by PAS

    Competitiveness Indices for Irish Manufactured Exports. Quarterly Economic Commentary Special Article, July 1981

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    This paper is devoted primarily to the construction of competitiveness indices for Irish manufactured exports. Our principal motivation in conducting such an exercise is the fact that no satisf a,ctory measures of competitiveness have as yet been developed for Ireland despite which the concept of competitiveness, and the problems assoicated with declining competitiveness in particular, frequently figure in public discussions of Ireland's economic performance. This concern is exemplified, for instance, by the fact that it is a recurring theme in the Quarterly Bulletins and Annual Reports of the Central Bank

    Density mapping with weak lensing and phase information

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    The available probes of the large scale structure in the Universe have distinct properties: galaxies are a high resolution but biased tracer of mass, while weak lensing avoids such biases but, due to low signal-to-noise ratio, has poor resolution. We investigate reconstructing the projected density field using the complementarity of weak lensing and galaxy positions. We propose a maximum-probability reconstruction of the 2D lensing convergence with a likelihood term for shear data and a prior on the Fourier phases constructed from the galaxy positions. By considering only the phases of the galaxy field, we evade the unknown value of the bias and allow it to be calibrated by lensing on a mode-by-mode basis. By applying this method to a realistic simulated galaxy shear catalogue, we find that a weak prior on phases provides a good quality reconstruction down to scales beyond l=1000, far into the noise domain of the lensing signal alone.Comment: 11 pages, 9 figures, published in MNRA
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