12,965 research outputs found
A High Precision, Optical Polarimeter to Measure Inclinations of High Mass X-Ray Binaries
We present commissioning data for the POLISH instrument obtained on the Hale
5-m telescope. The goal of this high precision polarimeter is to constrain
orbital inclination of high mass X-ray binaries and to therefore obtain
independent mass estimates for their black hole companions. We have obtained
photon shot noise limited precision on standard stars, and we have measured the
polarization of bright stars at the part per million level on a nightly basis.
Systematic effects have been reduced to less than 1% of the measured
polarization for polarized sources and to the part per million level for weakly
polarized sources. The high sensitivity of this instrument to asymmetry
suggests that valuable contributions will be made in many other fields,
including studies of extrasolar planets, debris disks, and stellar
astrophysics.Comment: 35 pages, 10 figures, accepted for publication in PAS
Frequency tuning of a triply-resonant whispering-gallery mode resonator to MHz wide transitions for proposed quantum repeater schemes
Quantum repeaters rely on an interfacing of flying qubits with quantum
memories. The most common implementations include a narrowband single photon
matched in bandwidth and central frequency to an atomic system. Previously, we
demonstrated the compatibility of our versatile source of heralded single
photons, which is based on parametric down-conversion in a triply-resonant
whispering-gallery mode resonator, with alkaline transitions [Schunk et al.,
Optica 2, 773 (2015)]. In this paper, we analyze our source in terms of phase
matching, available wavelength-tuning mechanisms, and applications to
narrow-band atomic systems. We resonantly address the D1 transitions of cesium
and rubidium with this optical parametric oscillator pumped above its
oscillation threshold. Below threshold, the efficient coupling of single
photons to atomic transitions heralded by single telecom-band photons is
demonstrated. Finally, we present an accurate analytical description of our
observations. Providing the demonstrated flexibility in connecting various
atomic transitions with telecom wavelengths, we show a promising approach to
realize an essential building block for quantum repeaters.Comment: 18 pages, 14 figure
High precision simulations of weak lensing effect on Cosmic Microwave Background polarization
We study accuracy, robustness and self-consistency of pixel-domain
simulations of the gravitational lensing effect on the primordial CMB
anisotropies due to the large-scale structure of the Universe. In particular,
we investigate dependence of the results precision on some crucial parameters
of such techniques and propose a semi-analytic framework to determine their
values so the required precision is a priori assured and the numerical workload
simultaneously optimized. Our focus is on the B-mode signal but we discuss also
other CMB observables, such as total intensity, T, and E-mode polarization,
emphasizing differences and similarities between all these cases. Our
semi-analytic considerations are backed up by extensive numerical results.
Those are obtained using a code, nicknamed lenS2HAT -- for Lensing using
Scalable Spherical Harmonic Transforms (S2HAT) -- which we have developed in
the course of this work. The code implements a version of the pixel-domain
approach of Lewis (2005) and permits performing the simulations at very high
resolutions and data volumes, thanks to its efficient parallelization provided
by the S2HAT library -- a parallel library for a calculation of the spherical
harmonic transforms. The code is made publicly available.Comment: 20 pages, 14 figures, submitted to A&A, matches version accepted for
publication in A&
Hong-Ou-Mandel interferometry on a biphoton beat note
Hong-Ou-Mandel interference, the fact that identical photons that arrive
simultaneously on different input ports of a beam splitter bunch into a common
output port, can be used to measure optical delays between different paths. It
is generally assumed that great precision in the measurement requires that
photons contain many frequencies, i.e., a large bandwidth. Here we challenge
this well-known assumption and show that the use of two well-separated
frequencies embedded in a quantum entangled state (discrete color entanglement)
suffices to achieve great precision. We determine optimum working points using
a Fisher Information analysis and demonstrate the experimental feasibility of
this approach by detecting thermally-induced delays in an optical fiber. These
results may significantly facilitate the use of quantum interference for
quantum sensing, by avoiding some stringent conditions such as the requirement
for large bandwidth signals
Precision Spectroscopy at Heavy Ion Ring Accelerator SIS300
Unique spectroscopic possibilities open up if a laser beam interacts with
relativistic lithium-like ions stored in the heavy ion ring accelerator SIS300
at the future Facility for Antiproton and Ion Research FAIR in Darmstadt,
Germany. At a relativistic factor gamma = 36 the 2P 1/2 level can be excited
from the 2S 1/2 ground state for any element with frequency doubled dye-lasers
in collinear geometry. Precise transition energy measurements can be performed
if the fluorescence photons, boosted in forward direction into the X-ray
region, are energetically analyzed with a single crystal monochromator. The
hyperfine structure can be investigated at the 2P 1/2 - 2S 1/2 transition for
all elements and at the 2P 3/2 - 2S 1/2 transition for elements with Z < 50.
Isotope shifts and nuclear moments can be measured with unprecedented
precision, in principle even for only a few stored radioactive species with
known nuclear spin. A superior relative line width in the order of 5E-7 may be
feasible after laser cooling, and even polarized external beams may be prepared
by optical pumping
A Full-Potential-Linearized-Augmented-Plane-Wave Electronic Structure Study of delta-Plutonium and the (001) Surface
The electronic and geometric properties of bulk fcc delta-plutonium and the
quantum size effects in the surface energies and the work functions of the
(001) ultra thin films (UTF) up to 7 layers have been investigated with
periodic density functional theory calculations within the full-potential
linearized augmented-plane wave (FP-LAPW) approach as implemented in the WIEN2k
package. Our calculated equilibrium atomic volume of 178.3 a.u.^3 and bulk
modulus of 24.9 GPa at the fully relativistic level of theory, i.e.
spin-polarization and spin-orbit coupling included, are in good agreement with
the experimental values of 168.2 a.u.^3 and 25 GPa (593 K), respectively. The
calculated equilibrium lattice constants at different levels of approximation
are used in the surface properties calculations for the thin films. The surface
energy is found to be rapidly converged with the semi-infinite surface energy
predicted to be 0.692eV at the fully-relativistic level.Comment: 27 pages,8 figure
All-sky signals from recombination to reionization with the SKA
Cosmic evolution in the hydrogen content of the Universe through
recombination and up to the end of reionization is expected to be revealed as
subtle spectral features in the uniform extragalactic cosmic radio background.
The redshift evolution in the excitation temperature of the 21-cm spin flip
transition of neutral hydrogen appears as redshifted emission and absorption
against the cosmic microwave background. The precise signature of the spectral
trace from cosmic dawn and the epoch of reionization are dependent on the
spectral radiance, abundance and distribution of the first bound systems of
stars and early galaxies, which govern the evolution in the spin-flip level
populations. Redshifted 21 cm from these epochs when the spin temperature
deviates from the temperature of the ambient relic cosmic microwave background
results in an all-sky spectral structure in the 40-200 MHz range, almost wholly
within the band of SKA-Low. Another spectral structure from gas evolution is
redshifted recombination lines from epoch of recombination of hydrogen and
helium; the weak all-sky spectral structure arising from this event is best
detected at the upper end of the 350-3050 MHz band of SKA-mid. Total power
spectra of SKA interferometer elements form the measurement set for these faint
signals from recombination and reionization; the inter-element interferometer
visibilities form a calibration set. The challenge is in precision polarimetric
calibration of the element spectral response and solving for additives and
unwanted confusing leakages of sky angular structure modes into spectral modes.
Herein we discuss observing methods and design requirements that make possible
these all-sky SKA measurements of the cosmic evolution of hydrogen.Comment: Accepted for publication in the SKA Science Book 'Advancing
Astrophysics with the Square Kilometre Array', to appear in 201
On the detection of spectral ripples from the Recombination Epoch
Photons emitted during the epochs of Hydrogen () and Helium recombination ( for HeII
HeI, for HeIII
HeII) are predicted to appear as broad, weak spectral distortions of the Cosmic
Microwave Background. We present a feasibility study for a ground-based
experimental detection of these recombination lines, which would provide an
observational constraint on the thermal ionization history of the Universe,
uniquely probing astrophysical cosmology beyond the last scattering surface. We
find that an octave band in the 2--6 GHz window is optimal for such an
experiment, both maximizing signal-to-noise ratio and including sufficient line
spectral structure. At these frequencies the predicted signal appears as an
additive quasi-sinusoidal component with amplitude about nK that is
embedded in a sky spectrum some nine orders of magnitude brighter. We discuss
an algorithm to detect these tiny spectral fluctuations in the sky spectrum by
foreground modeling. We introduce a \textit{Maximally Smooth} function capable
of describing the foreground spectrum and distinguishing the signal of
interest. With Bayesian statistical tests and mock data we estimate that a
detection of the predicted distortions is possible with 90\% confidence by
observing for 255 days with an array of 128 radiometers using cryogenically
cooled state-of-the-art receivers. We conclude that detection is in principle
feasible in realistic observing times; we propose APSERa---Array of Precision
Spectrometers for the Epoch of Recombination---a dedicated radio telescope to
detect these recombination lines.Comment: 33 pages, 16 figures, submitted to ApJ, comments welcom
Calibrating CHIME, A New Radio Interferometer to Probe Dark Energy
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit
interferometer currently being built at the Dominion Radio Astrophysical
Observatory (DRAO) in Penticton, BC, Canada. We will use CHIME to map neutral
hydrogen in the frequency range 400 -- 800\,MHz over half of the sky, producing
a measurement of baryon acoustic oscillations (BAO) at redshifts between 0.8 --
2.5 to probe dark energy. We have deployed a pathfinder version of CHIME that
will yield constraints on the BAO power spectrum and provide a test-bed for our
calibration scheme. I will discuss the CHIME calibration requirements and
describe instrumentation we are developing to meet these requirements
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