8,152 research outputs found
Wiener filtering with a seismic underground array at the Sanford Underground Research Facility
A seismic array has been deployed at the Sanford Underground Research
Facility in the former Homestake mine, South Dakota, to study the underground
seismic environment. This includes exploring the advantages of constructing a
third-generation gravitational-wave detector underground. A major noise source
for these detectors would be Newtonian noise, which is induced by fluctuations
in the local gravitational field. The hope is that a combination of a low-noise
seismic environment and coherent noise subtraction using seismometers in the
vicinity of the detector could suppress the Newtonian noise to below the
projected noise floor for future gravitational-wave detectors. In this paper,
we use Wiener filtering techniques to subtract coherent noise in a seismic
array in the frequency band 0.05 -- 1\,Hz. This achieves more than an order of
magnitude noise cancellation over a majority of this band. We show how this
subtraction would benefit proposed future low-frequency gravitational wave
detectors. The variation in the Wiener filter coefficients over the course of
the day, including how local activities impact the filter, is analyzed. We also
study the variation in coefficients over the course of a month, showing the
stability of the filter with time. How varying the filter order affects the
subtraction performance is also explored. It is shown that optimizing filter
order can significantly improve subtraction of seismic noise, which gives hope
for future gravitational-wave detectors to address Newtonian noise
Quantitative test of general theories of the intrinsic laser linewidth
We perform a first-principles calculation of the quantum-limited laser
linewidth, testing the predictions of recently developed theories of the laser
linewidth based on fluctuations about the known steady-state laser solutions
against traditional forms of the Schawlow-Townes linewidth. The numerical study
is based on finite-difference time-domain simulations of the semiclassical
Maxwell-Bloch lasing equations, augmented with Langevin force terms, and thus
includes the effects of dispersion, losses due to the open boundary of the
laser cavity, and non-linear coupling between the amplitude and phase
fluctuations ( factor). We find quantitative agreement between the
numerical results and the predictions of the noisy steady-state ab initio laser
theory (N-SALT), both in the variation of the linewidth with output power, as
well as the emergence of side-peaks due to relaxation oscillations.Comment: 24 pages, 10 figure
Permanent Electric Dipole Moments of Single-, Two-, and Three-Nucleon Systems
A nonzero electric dipole moment (EDM) of the neutron, proton, deuteron or
helion, in fact, of any finite system necessarily involves the breaking of a
symmetry, either by the presence of external fields (i.e. electric fields
leading to the case of induced EDMs) or explicitly by the breaking of the
discrete parity and time-reflection symmetries in the case of permanent EDMs.
We discuss two theorems describing these phenomena and report about the
cosmological motivation for an existence of CP breaking beyond what is
generated by the Kobayashi-Maskawa mechanism in the Standard Model and what
this might imply for the permanent electric dipole moments of the nucleon and
light nuclei by estimating a window of opportunity for physics beyond what is
currently known. Recent - and in the case of the deuteron even unpublished -
results for the relevant matrix elements of nuclear EDM operators are presented
and the relevance for disentangling underlying New Physics sources are
discussed.Comment: 20 pages, chapter for the memorial book "Gerry Brown 90", final
version, some typos correcte
On line power spectra identification and whitening for the noise in interferometric gravitational wave detectors
In this paper we address both to the problem of identifying the noise Power
Spectral Density of interferometric detectors by parametric techniques and to
the problem of the whitening procedure of the sequence of data. We will
concentrate the study on a Power Spectral Density like the one of the
Italian-French detector VIRGO and we show that with a reasonable finite number
of parameters we succeed in modeling a spectrum like the theoretical one of
VIRGO, reproducing all its features. We propose also the use of adaptive
techniques to identify and to whiten on line the data of interferometric
detectors. We analyze the behavior of the adaptive techniques in the field of
stochastic gradient and in the
Least Squares ones.Comment: 28 pages, 21 figures, uses iopart.cls accepted for pubblication on
Classical and Quantum Gravit
Noise parametric identification and whitening for LIGO 40-meter interferometer data
We report the analysis we made on data taken by Caltech 40-meter prototype
interferometer to identify the noise power spectral density and to whiten the
sequence of noise. We concentrate our study on data taken in November 1994, in
particular we analyzed two frames of data: the 18nov94.2.frame and the
19nov94.2.frame.
We show that it is possible to whiten these data, to a good degree of
whiteness, using a high order whitening filter. Moreover we can choose to
whiten only restricted band of frequencies around the region we are interested
in, obtaining a higher level of whiteness.Comment: 11 pages, 15 figures, accepted for publication by Physical Review
Characterization of disturbance sources for LISA: torsion pendulum results
A torsion pendulum allows ground-based investigation of the purity of
free-fall for the LISA test masses inside their capacitive position sensor.
This paper presents recent improvements in our torsion pendulum facility that
have both increased the pendulum sensitivity and allowed detailed
characterization of several important sources of acceleration noise for the
LISA test masses. We discuss here an improved upper limit on random force noise
originating in the sensor. Additionally, we present new measurement techniques
and preliminary results for characterizing the forces caused by the sensor's
residual electrostatic fields, dielectric losses, residual spring-like
coupling, and temperature gradients.Comment: 11 pages, 8 figures, accepted for publication Classical and Quantum
Gravit
Measuring the photon distribution by ON/OFF photodectors
Reconstruction of photon statistics of optical states provide fundamental
information on the nature of any optical field and find various relevant
applications. Nevertheless, no detector that can reliably discriminate the
number of incident photons is available. On the other hand the alternative of
reconstructing density matrix by quantum tomography leads to various technical
difficulties that are particular severe in the pulsed regime (where mode
matching between signal an local oscillator is very challenging). Even if
on/off detectors, as usual avalanche PhotoDiodes operating in Geiger mode, seem
useless as photocounters, recently it was shown how reconstruction of photon
statistics is possible by considering a variable quantum efficiency. Here we
present experimental reconstructions of photon number distributions of both
continuous-wave and pulsed light beams in a scheme based on on/off avalanche
photodetection assisted by maximum-likelihood estimation. Reconstructions of
the distribution for both semiclassical and quantum states of light (as single
photon, coherent, pseudothermal and multithermal states) are reported for
single-mode as well as for multimode beams. The stability and good accuracy
obtained in the reconstruction of these states clearly demonstrate the
interesting potentialities of this simple technique.Comment: 6 pages, 7 figures, to appear on Laser Physic
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