2,082 research outputs found
Vortex sorter for Bose-Einstein condensates
We have designed interferometers that sort Bose-Einstein condensates into
their vortex components. The Bose-Einstein condensates in the two arms of the
interferometer are rotated with respect to each other through fixed angles;
different vortex components then exit the interferometer in different
directions. The method we use to rotate the Bose-Einstein condensates involves
asymmetric phase imprinting and is itself new. We have modelled rotation
through fixed angles and sorting into vortex components with even and odd
values of the topological charge of 2-dimensional Bose-Einstein condensates in
a number of states (pure or superposition vortex states for different values of
the scattering length). Our scheme may have applications for quantum
information processing.Comment: 4 pages, high resolution figures can be obtained from the author
Systematic challenges for future gravitational wave measurements of precessing binary black holes
The properties of precessing, coalescing binary black holes are presently
inferred through comparison with two approximate models of compact binary
coalescence. In this work we show these two models often disagree substantially
when binaries have modestly large spins () and modest mass ratios
(). We demonstrate these disagreements using standard figures of
merit and the parameters inferred for recent detections of binary black holes.
By comparing to numerical relativity, we confirm these disagreements reflect
systematic errors. We provide concrete examples to demonstrate that these
systematic errors can significantly impact inferences about astrophysically
significant binary parameters. For the immediate future, parameter inference
for binary black holes should be performed with multiple models (including
numerical relativity), and carefully validated by performing inference under
controlled circumstances with similar synthetic events.Comment: 12 pages, 9 figure
Studying stellar binary systems with the Laser Interferometer Space Antenna using Delayed Rejection Markov chain Monte Carlo methods
Bayesian analysis of LISA data sets based on Markov chain Monte Carlo methods
has been shown to be a challenging problem, in part due to the complicated
structure of the likelihood function consisting of several isolated local
maxima that dramatically reduces the efficiency of the sampling techniques.
Here we introduce a new fully Markovian algorithm, a Delayed Rejection
Metropolis-Hastings Markov chain Monte Carlo method, to efficiently explore
these kind of structures and we demonstrate its performance on selected LISA
data sets containing a known number of stellar-mass binary signals embedded in
Gaussian stationary noise.Comment: 12 pages, 4 figures, accepted in CQG (GWDAW-13 proceedings
An optimised system for generating multi-resolution DTMS using NASA DTMS datasets
Abstract. Within the EU FP-7 iMars project, a fully automated multi-resolution DTM processing chain, called Co-registration ASP-Gotcha Optimised (CASP-GO) has been developed, based on the open source NASA Ames Stereo Pipeline (ASP). CASP-GO includes tiepoint based multi-resolution image co-registration and an adaptive least squares correlation-based sub-pixel refinement method called Gotcha. The implemented system guarantees global geo-referencing compliance with respect to HRSC (and thence to MOLA), provides refined stereo matching completeness and accuracy based on the ASP normalised cross-correlation. We summarise issues discovered from experimenting with the use of the open-source ASP DTM processing chain and introduce our new working solutions. These issues include global co-registration accuracy, de-noising, dealing with failure in matching, matching confidence estimation, outlier definition and rejection scheme, various DTM artefacts, uncertainty estimation, and quality-efficiency trade-offs
Feedback control of thermal lensing in a high optical power cavity
This paper reports automatic compensation of strong thermal lensing in a suspended 80 m optical cavity with sapphire test mass mirrors. Variation of the transmitted beam spot size is used to obtain an error signal to control the heating power applied to the cylindrical surface of an intracavity compensation plate. The negative thermal lens created in the compensation plate compensates the positive thermal lens in the sapphire test mass, which was caused by the absorption of the high intracavity optical power. The results show that feedback control is feasible to compensate the strong thermal lensing expected to occur in advanced laser interferometric gravitational wave detectors. Compensation allows the cavity resonance to be maintained at the fundamental mode, but the long thermal time constant for thermal lensing control in fused silica could cause difficulties with the control of parametric instabilities.This research was supported by the Australian
Research Council and the Department of Education,
Science and Training and by the U.S. National Science Foundation,
through LIGO participation in the HOPF
A Bayesian approach to the follow-up of candidate gravitational wave signals
Ground-based gravitational wave laser interferometers (LIGO, GEO-600, Virgo
and Tama-300) have now reached high sensitivity and duty cycle. We present a
Bayesian evidence-based approach to the search for gravitational waves, in
particular aimed at the followup of candidate events generated by the analysis
pipeline. We introduce and demonstrate an efficient method to compute the
evidence and odds ratio between different models, and illustrate this approach
using the specific case of the gravitational wave signal generated during the
inspiral phase of binary systems, modelled at the leading quadrupole Newtonian
order, in synthetic noise. We show that the method is effective in detecting
signals at the detection threshold and it is robust against (some types of)
instrumental artefacts. The computational efficiency of this method makes it
scalable to the analysis of all the triggers generated by the analysis
pipelines to search for coalescing binaries in surveys with ground-based
interferometers, and to a whole variety of signal waveforms, characterised by a
larger number of parameters.Comment: 9 page
Bayesian coherent analysis of in-spiral gravitational wave signals with a detector network
The present operation of the ground-based network of gravitational-wave laser
interferometers in "enhanced" configuration brings the search for gravitational
waves into a regime where detection is highly plausible. The development of
techniques that allow us to discriminate a signal of astrophysical origin from
instrumental artefacts in the interferometer data and to extract the full range
of information are some of the primary goals of the current work. Here we
report the details of a Bayesian approach to the problem of inference for
gravitational wave observations using a network of instruments, for the
computation of the Bayes factor between two hypotheses and the evaluation of
the marginalised posterior density functions of the unknown model parameters.
The numerical algorithm to tackle the notoriously difficult problem of the
evaluation of large multi-dimensional integrals is based on a technique known
as Nested Sampling, which provides an attractive alternative to more
traditional Markov-chain Monte Carlo (MCMC) methods. We discuss the details of
the implementation of this algorithm and its performance against a Gaussian
model of the background noise, considering the specific case of the signal
produced by the in-spiral of binary systems of black holes and/or neutron
stars, although the method is completely general and can be applied to other
classes of sources. We also demonstrate the utility of this approach by
introducing a new coherence test to distinguish between the presence of a
coherent signal of astrophysical origin in the data of multiple instruments and
the presence of incoherent accidental artefacts, and the effects on the
estimation of the source parameters as a function of the number of instruments
in the network.Comment: 22 page
Power scalable TEM(oo) CW Nd: YAG laser with thermal lens compensation
We present finite-element analyzes and experimental results to validate our approach for building high-power single-mode Nd:YAG lasers. We show that the thermooptical and thermomechanical properties of a slab laser can be controlled. This is essential for the use of the proposed unstable resonator. We include demonstration of an efficient subscale laser operating at 20 W TEM00.D. Mudge, M. Ostermeyer, P. J. Veitch, J. Munch, B. Middlemiss, D. J. Ottaway and M. W. Hamilto
Compensation of Strong Thermal Lensing in High Optical Power Cavities
In an experiment to simulate the conditions in high optical power advanced
gravitational wave detectors such as Advanced LIGO, we show that strong thermal
lenses form in accordance with predictions and that they can be compensated
using an intra-cavity compensation plate heated on its cylindrical surface. We
show that high finesse ~1400 can be achieved in cavities with internal
compensation plates, and that the cavity mode structure can be maintained by
thermal compensation. It is also shown that the measurements allow a direct
measurement of substrate optical absorption in the test mass and the
compensation plate.Comment: 8 page
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