4,344 research outputs found
Transport mechanisms in low-resistance ohmic contacts to p-InP formed by rapid thermal annealing
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 -ordered operator product, where the value of 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 with the vacuum
. 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
- …