12,237 research outputs found
Recovery of continuous wave squeezing at low frequencies
We propose and demonstrate a system that produces squeezed vacuum using a
pair of optical parametric amplifiers. This scheme allows the production of
phase sidebands on the squeezed vacuum which facilitate phase locking in
downstream applications. We observe strong, stably locked, continuous wave
vacuum squeezing at frequencies as low as 220 kHz. We propose an alternative
resonator configuration to overcome low frequency squeezing degradation caused
by the optical parametric amplifiers.Comment: 9 pages, 4 figure
Workplace stress among construction professionals in South Africa: The role of harassment and discrimination
The discrimination/harassment experiences of survey respondents in different construction professional groups in SouthAfrica is compared, and the relationship between harassment/discrimination and perceived work stress is examined
A FUSE survey of high-latitude Galactic molecular hydrogen
Measurements of molecular hydrogen (H_2) column densities are presented for
the first six rotational levels (J=0 to 5) for 73 extragalactic targets
observed with FUSE. All of these have a final signal-to-noise ratio larger than
\snlimit, and are located at galactic latitude |b|>20 deg. The individual
observations were calibrated with the FUSE calibration pipeline CalFUSE version
2.1 or higher, and then carefully aligned in velocity. The final velocity
shifts for all the FUSE segments are listed. H_2 column densities or limits are
determined for the 6 lowest rotational (J) levels for each HI component in the
line of sight, using a curve-of-growth approach at low column densities ~16.5),
and Voigt-profile fitting at higher column densities. Detections include 73
measurements of low-velocity H_2 in the Galactic Disk and lower Halo. Eight
sightlines yield non-detections for Galactic H_2. The measured column densities
range from log N(H_2)=14 to log N(H_2)=20. Strong correlations are found
between log N(H_2) and T_01, the excitation temperature of the H_2, as well as
between log N(H_2) and the level population ratios (log (N(J')/N(J))). The
average fraction of nuclei in molecular hydrogen (f(H_2)) in each sightline is
calculated; however, because there are many HI clouds in each sightline, the
physics of the transition from HI to H_2 can not be studied. Detections also
include H2 in 16 intermediate-velocity clouds in the Galactic Halo (out of 35
IVCs). Molecular hydrogen is seen in one high-velocity cloud (the Leading Arm
of the Magellanic Stream), although 19 high-velocity clouds are intersected;
this strongly suggests that dust is rare or absent in these objects. Finally,
there are five detections of H_2 in external galaxies.Comment: Accepted for ApJ Supplement. Note: figs 7 and 8 not included because
astro-ph rejects them as too bi
Cavity optoelectromechanical regenerative amplification
Cavity optoelectromechanical regenerative amplification is demonstrated. An
optical cavity enhances mechanical transduction, allowing sensitive measurement
even for heavy oscillators. A 27.3 MHz mechanical mode of a microtoroid was
linewidth narrowed to 6.6\pm1.4 mHz, 30 times smaller than previously achieved
with radiation pressure driving in such a system. These results may have
applications in areas such as ultrasensitive optomechanical mass spectroscopy
Colloidal Processing and sintering of nanosized transition aluminas
The dispersion of nanosized gamma aluminas with high specific surfaces areas (100 m2 /g) and primary particle sizes around 20 nm, using polyacrylic acid, has been investigated. The effect of pH and polymer concentration showed that the highest density green bodies were produced using high polymer concentrations (6 wt.%) and pH of 6. Interparticle potential calculations have been made and help explain the underlying dispersion mechanism at least on a qualitative level. The dispersions were then used to slip cast green bodies followed by drying and sintering. The types of gamma alumina powder have been investigated, the pure gamma alumina, doped with MgO and also with the addition of alpha alumina seeds. The high degree of agglomeration of the gamma alumina powders led to very low densities (60%) even the alpha seeded alumina reached only 85% theoretical density. Attrition milling with zirconia media improves both green density and sintered densities significantly with all powders showing sintered densities >97%. Microstructural analysis on polished and etched surfaces show, however, that the grain sizes are well above 1 Am over 50 times greater than the initial gamma alumina primary particles. A two-step sintering cycle was investigated with the Mg doped powder and average grain sizes around 580 nm were achieved
Quantum limited particle sensing in optical tweezers
Particle sensing in optical tweezers systems provides information on the
position, velocity and force of the specimen particles. The conventional
quadrant detection scheme is applied ubiquitously in optical tweezers
experiments to quantify these parameters. In this paper we show that quadrant
detection is non-optimal for particle sensing in optical tweezers and propose
an alternative optimal particle sensing scheme based on spatial homodyne
detection. A formalism for particle sensing in terms of transverse spatial
modes is developed and numerical simulations of the efficacy of both quadrant
and spatial homodyne detection are shown. We demonstrate that an order of
magnitude improvement in particle sensing sensitivity can be achieved using
spatial homodyne over quadrant detection.Comment: Submitted to Biophys
Squeezing and entanglement delay using slow light
We examine the interaction of a weak probe with atoms in a lambda-level
configuration under the conditions of electromagnetically induced transparency
(EIT). In contrast to previous works on EIT, we calculate the output state of
the resultant slowly propagating light field while taking into account the
effects of ground state dephasing and atomic noise for a more realistic model.
In particular, we propose two experiments using slow light with a nonclassical
probe field and show that two properties of the probe, entanglement and
squeezing, characterizing the quantum state of the probe field, can be
well-preserved throughout the passage.Comment: 2 figures; v2: fixed some minor typographical errors in a couple of
equations and corrected author spelling in one reference. v3: Added three
authors; changed the entaglement definition to conform to a more accepted
standard (Duan's entanglement measure); altered the abstract slightly. v4:
fixed formatting of figure
The Dust Content of Galaxy Clusters
We report on the detection of reddening toward z ~ 0.2 galaxy clusters. This
is measured by correlating the Sloan Digital Sky Survey cluster and quasar
catalogs and by comparing the photometric and spectroscopic properties of
quasars behind the clusters to those in the field. We find mean E(B-V) values
of a few times 10^-3 mag for sight lines passing ~Mpc from the clusters'
center. The reddening curve is typical of dust but cannot be used to
distinguish between different dust types. The radial dependence of the
extinction is shallow near the cluster center suggesting that most of the
detected dust lies at the outskirts of the clusters. Gravitational
magnification of background z ~ 1.7 sources seen on Mpc (projected) scales
around the clusters is found to be of order a few per cent, in qualitative
agreement with theoretical predictions. Contamination by different spectral
properties of the lensed quasar population is unlikely but cannot be excluded.Comment: 4 pages, 3 figure
Dephasing representation of quantum fidelity for general pure and mixed states
General semiclassical expression for quantum fidelity (Loschmidt echo) of
arbitrary pure and mixed states is derived. It expresses fidelity as an
interference sum of dephasing trajectories weighed by the Wigner function of
the initial state, and does not require that the initial state be localized in
position or momentum. This general dephasing representation is special in that,
counterintuitively, all of fidelity decay is due to dephasing and none due to
the decay of classical overlaps. Surprising accuracy of the approximation is
justified by invoking the shadowing theorem: twice--both for physical
perturbations and for numerical errors. It is shown how the general expression
reduces to the special forms for position and momentum states and for wave
packets localized in position or momentum. The superiority of the general over
the specialized forms is explained and supported by numerical tests for wave
packets, non-local pure states, and for simple and random mixed states. The
tests are done in non-universal regimes in mixed phase space where detailed
features of fidelity are important. Although semiclassically motivated, present
approach is valid for abstract systems with a finite Hilbert basis provided
that the discrete Wigner transform is used. This makes the method applicable,
via a phase space approach, e. g., to problems of quantum computation.Comment: 11 pages, 4 figure
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