Entanglement and Quantum Phase Transitions via Adiabatic Quantum Computation

For a finite XY chain and a finite two-dimensional Ising lattice, it is shown that the paramagnetic ground state is adiabatically transformed to the GHZ state in the ferromagnetic phase by slowly turning on the magnetic field. The fidelity between the GHZ state and an adiabatically evolved state shows a feature of the quantum phase transition.Comment: Revise

Cosmic Microwave Background Anisotropy Window Functions Revisited

The primary results of most observations of cosmic microwave background (CMB) anisotropy are estimates of the angular power spectrum averaged through some broad band, called band-powers. These estimates are in turn what are used to produce constraints on cosmological parameters due to all CMB observations. Essential to this estimation of cosmological parameters is the calculation of the expected band-power for a given experiment, given a theoretical power spectrum. Here we derive the "band power" window function which should be used for this calculation, and point out that it is not equivalent to the window function used to calculate the variance. This important distinction has been absent from much of the literature: the variance window function is often used as the band-power window function. We discuss the validity of this assumed equivalence, the role of window functions for experiments that constrain the power in {\it multiple} bands, and summarize a prescription for reporting experimental results. The analysis methods detailed here are applied in a companion paper to three years of data from the Medium Scale Anisotropy Measurement.Comment: 5 pages, 1 included .eps figure, PRD in press---final published versio

How well can we measure and understand foregrounds with 21 cm experiments?

Before it becomes a sensitive probe of the Epoch of Reionization, the Dark Ages, and fundamental physics, 21 cm tomography must successfully contend with the issue of foreground contamination. Broadband foreground sources are expected to be roughly four orders of magnitude larger than any cosmological signals, so precise foreground models will be necessary. Such foreground models often contain a large number of parameters, reflecting the complicated physics that governs foreground sources. In this paper, we concentrate on spectral modeling (neglecting, for instance, bright point source removal from spatial maps) and show that 21 cm tomography experiments will likely not be able to measure these parameters without large degeneracies, simply because the foreground spectra are so featureless and generic. However, we show that this is also an advantage, because it means that the foregrounds can be characterized to a high degree of accuracy once a small number of parameters (likely three or four, depending on one's instrumental specifications) are measured. This provides a simple understanding for why 21 cm foreground subtraction schemes are able to remove most of the contaminants by suppressing just a small handful of simple spectral forms. In addition, this suggests that the foreground modeling process should be relatively simple and will likely not be an impediment to the foreground subtraction schemes that are necessary for a successful 21 cm tomography experiment.Comment: 15 pages, 9 figures, 2 tables; Replaced with accepted MNRAS version (slight quantitative changes to plots and tables, no changes to any conclusions

Realistic Simulations of the Galactic Polarized Foreground: Consequences for 21-cm Reionization Detection Experiments

Experiments designed to measure the redshifted 21~cm line from the Epoch of Reionization (EoR) are challenged by strong astrophysical foreground contamination, ionospheric distortions, complex instrumental response and other different types of noise (e.g. radio frequency interference). The astrophysical foregrounds are dominated by diffuse synchrotron emission from our Galaxy. Here we present a simulation of the Galactic emission used as a foreground module for the LOFAR- EoR key science project end-to-end simulations. The simulation produces total and polarized intensity over $10^\circ \times 10^\circ$ maps of the Galactic synchrotron and free-free emission, including all observed characteristics of the emission: spatial fluctuations of amplitude and spectral index of the synchrotron emission, together with Faraday rotation effects. The importance of these simulations arise from the fact that the Galactic polarized emission could behave in a manner similar to the EoR signal along the frequency direction. As a consequence, an improper instrumental calibration will give rise to leakages of the polarized to the total signal and mask the desired EoR signal. In this paper we address this for the first time through realistic simulations.Comment: 14 pages, 8 figures, published in MNRA

Enhanced adhesion of polypyrrole/PW12O40 3- hybrid coatings on polyester fabrics

Polyester fabrics have been treated with plasma to increase polypyrrole/PW12O40 3- (hybrid material) adhesion to its surface. With the plasma treatment, the roughness of the fibers increases as it has been observed by means of atomic force microscopy (AFM). Polar functional groups are also created on the surface of polyester fabrics as X-ray photoelectron spectroscopy (XPS) measurements have shown. These polar groups contribute to the adhesion of polypyrrole to the fibers. Coatings obtained on plasma treated fabrics were more resistant to washing and rubbing fastness tests. The use of an inorganic counter ion (PW12O 403-) that contains an element with a high atomic number (W) helps to locate zones where the coating is missed; this is achieved by means of micrographs obtained by backscattered electrons (BSE). The electrical resistance of the fabrics was also measured by electrochemical impedance spectroscopy (EIS), obtaining also better results with the plasma treated fabrics. Copyright © 2012 Wiley Periodicals, Inc.Authors thank to the Spanish Ministerio de Ciencia e Innovación (contracts CTM2010-18842-C02-02 and CTM2011-23583) and Universitat Politècnica de València (Primeros Proyectos de Investigación (PAID-06-10)) for the financial support. J. Molina is grateful to the Conselleria d'Educació (Generalitat Valenciana) for the FPI fellowship

The contribution of star-forming galaxies to the cosmic radio background

Recent measurements of the temperature of the sky in the radio band, combined with literature data, have convincingly shown the existence of a cosmic radio background with an amplitude of $\sim 1$ K at 1 GHz and a spectral energy distribution that is well described by a power law with index $\alpha \simeq -0.6$. The origin of this signal remains elusive, and it has been speculated that it could be dominated by the contribution of star-forming galaxies at high redshift \change{if the far infrared-radio correlation $q(z)$ evolved} in time. \change{We fit observational data from several different experiments by the relation $q(z) \simeq q_0 - \beta \log(1+z)$ with $q_0 = 2.783 \pm 0.024$ and $\beta = 0.705 \pm 0.081$ and estimate the total radio emission of the whole galaxy population at any given redshift from the cosmic star formation rate density at that redshift. It is found that} star-forming galaxies can only account for $\sim$13 percent of the observed intensity of the cosmic radio background.Comment: 5 pages, 3 figure

Making Maps Of The Cosmic Microwave Background: The MAXIMA Example

This work describes Cosmic Microwave Background (CMB) data analysis algorithms and their implementations, developed to produce a pixelized map of the sky and a corresponding pixel-pixel noise correlation matrix from time ordered data for a CMB mapping experiment. We discuss in turn algorithms for estimating noise properties from the time ordered data, techniques for manipulating the time ordered data, and a number of variants of the maximum likelihood map-making procedure. We pay particular attention to issues pertinent to real CMB data, and present ways of incorporating them within the framework of maximum likelihood map-making. Making a map of the sky is shown to be not only an intermediate step rendering an image of the sky, but also an important diagnostic stage, when tests for and/or removal of systematic effects can efficiently be performed. The case under study is the MAXIMA data set. However, the methods discussed are expected to be applicable to the analysis of other current and forthcoming CMB experiments.Comment: Replaced to match the published version, only minor change

Will point sources spoil 21 cm tomography?

21 cm tomography is emerging as a promising probe of the cosmological dark ages and the epoch of reionization, as well as a tool for observational cosmology in general. However, serious sources of foreground contamination must be subtracted for experimental efforts to be viable. In this paper, we focus on the removal of unresolved extragalactic point sources with smooth spectra, and evaluate how the residual foreground contamination after cleaning depends on instrumental and algorithmic parameters. A crucial but often ignored complication is that the synthesized beam of an interferometer array shrinks towards higher frequency, causing complicated frequency structure in each sky pixel as "frizz" far from the beam center contracts across unresolved radio sources. We find that current-generation experiments should nonetheless be able to clean out this points source contamination adequately, and quantify the instrumental and algorithmic design specifications required to meet this foreground challenge.Comment: 14 pages, 17 figures, replaced to match accepted MNRAS versio