Efficient optical quantum state engineering

We discuss a novel method of efficiently producing multi-photon states using repeated spontaneous parametric downconversion. Specifically, by attempting downconversion several times, we can pseudo-deterministically add photons to a mode, producing various several-photon states. We discuss both expected performance and experimental limitations.Comment: 4 pages, 4 figure

Entanglement purification of multi-mode quantum states

An iterative random procedure is considered allowing an entanglement purification of a class of multi-mode quantum states. In certain cases, a complete purification may be achieved using only a single signal state preparation. A physical implementation based on beam splitter arrays and non-linear elements is suggested. The influence of loss is analyzed in the example of a purification of entangled N-mode coherent states.Comment: 6 pages, 3 eps-figures, using revtex

Causal connection in parsec-scale relativistic jets: results from the MOJAVE VLBI survey

We report that active galactic nucleus (AGN) jets are causally connected on parsec scales, based on 15 GHz Very Long Baseline Array (VLBA) data from a sample of 133 AGN jets. This result is achieved through a new method for measuring the product of the jet Lorentz factor and the intrinsic opening angle Gamma*theta_j from measured apparent opening angles in flux density limited samples of AGN jets. The Gamma*theta_j parameter is important for jet physics because it is related to the jet-frame sidewise expansion speed and causal connection between the jet edges and its symmetry axis. Most importantly, the standard model of jet production requires that the jet be causally connected with its symmetry axis, implying that Gamma*theta_j < 1. When we apply our method to the MOJAVE flux density limited sample of radio loud objects, we find Gamma*theta_j = 0.2, implying that AGN jets are causally connected. We also find evidence that AGN jets viewed very close to the line of sight effectively have smaller intrinsic opening angles compared with jets viewed more off-axis, which is consistent with Doppler beaming and a fast inner spine/slow outer sheath velocity field. Notably, gamma-ray burst (GRB) jets have a typical Gamma*theta_j that is two orders of magnitude higher, suggesting that different physical mechanisms are at work in GRB jets compared to AGN jets. A useful application of our result is that a jet's beaming parameters can be derived. Assuming Gamma*theta_j is approximately constant in the AGN jet population, an individual jet's Doppler factor and Lorentz factor (and therefore also its viewing angle) can be determined using two observable quantities: apparent jet opening angle and the apparent speed of jet components.Comment: 9 pages, 4 figure

Conditional quantum-state transformation at a beam splitter

Using conditional measurement on a beam splitter, we study the transformation of the quantum state of the signal mode within the concept of two-port non-unitary transformation. Allowing for arbitrary quantum states of both the input reference mode and the output reference mode on which the measurement is performed, we show that the non-unitary transformation operator can be given as an $s$-ordered operator product, where the value of $s$ is entirely determined by the absolute value of the beam splitter reflectance (or transmittance). The formalism generalizes previously obtained results that can be recovered by simple specification of the non-unitary transformation operator. As an application, we consider the generation of Schr\"odinger-cat-like states. An extension to mixed states and imperfect detection is outlined.Comment: 7 Postscript figures, using Late

LOGISTIC REGRESSION ANALYSIS TO DETERMINE FACTORS CONTRIBUTING TO SUMMER FEEDLOT DEATHS

Summer heat has already been identified as a major factor for cattle deaths in the feedlot. This study attempts to assess what other factors contribute to and/or influence cattle deaths. Identifying multiple factors that contribute to summer feedlot deaths could aid feedlot managers in implementation of mitigation strategies and minimize the loss of nearly finished cattle. Daily pen, cattle, and nutritional characteristics were recorded and included in this generalized linear mixed model analysis. Cattle data were obtained from cattle pens at a single location from July 1, 2010 to July 31, 2010. Hourly weather data were acquired from this feed yard while solar radiation was received from a neighboring town. Rather than using multiple weather variables, a single comprehensive climate index that summarizes several weather variables is used to capture the apparent feel of the weather. After reviewing the data, a statistical model is developed and odds ratios are computed for statistical inference. According to these odds ratios, cattle fed on severe west slopes had significantly higher odds of death than other types of slopes. Analysis of feed intake indicates pens consuming 16 pounds of feed per head or less during July 16 – 18 have higher odds of death than other consumption levels

Production of superpositions of coherent states in traveling optical fields with inefficient photon detection

We develop an all-optical scheme to generate superpositions of macroscopically distinguishable coherent states in traveling optical fields. It non-deterministically distills coherent state superpositions (CSSs) with large amplitudes out of CSSs with small amplitudes using inefficient photon detection. The small CSSs required to produce CSSs with larger amplitudes are extremely well approximated by squeezed single photons. We discuss some remarkable features of this scheme: it effectively purifies mixed initial states emitted from inefficient single photon sources and boosts negativity of Wigner functions of quantum states.Comment: 13 pages, 9 figures, to be published in Phys. Rev.

Heralded single-photon generation using imperfect single-photon sources and a two-photon-absorbing medium

We propose a setup for a heralded, i.e. announced generation of a pure single-photon state given two imperfect sources whose outputs are represented by mixtures of the single-photon Fock state $\ket{1}$ with the vacuum $\ket{0}$. Our purification scheme uses beam splitters, photodetection and a two-photon-absorbing medium. The admixture of the vacuum is fully eliminated. We discuss two potential realizations of the scheme.Comment: 22 pages, 8 figures (LaTeX). In version v2 we have slightly modified our setup so as to increase the success probability of single-photon generation by a factor of two. In addition, in an appendix we discuss alternative realizations of single-photon generation without a Mach-Zehnder interferometer. Three new figures have been added. Version v3 is a revised version published in Phys. Rev. A. It contains numerous minor corrections and clarifications. A new figure has been added in order to clarify our convention regarding labelling the field modes. The action of the beam splitters in the Schroedinger picture is introduced. A new reference has been include

Near-Constant Mean Curvature Solutions of the Einstein Constraint Equations with Non-Negative Yamabe Metrics

We show that sets of conformal data on closed manifolds with the metric in the positive or zero Yamabe class, and with the gradient of the mean curvature function sufficiently small, are mapped to solutions of the Einstein constraint equations. This result extends previous work which required the conformal metric to be in the negative Yamabe class, and required the mean curvature function to be nonzero.Comment: 15 page