52 research outputs found
Quantum improvement of time transfer between remote clocks
Exchanging light pulses to perform accurate space-time positioning is a
paradigmatic issue of physics. It is ultimately limited by the quantum nature
of light, which introduces fluctuations in the optical measurements and leads
to the so-called Standard Quantum Limit (SQL). We propose a new scheme
combining homodyne detection and mode-locked femtosecond lasers that lead to a
new SQL in time transfer, potentially reaching the yoctosecond range
(10^-21-10^-24 s). We prove that no other measurement strategy can lead to
better sensitivity with shot noise limited light. We then demonstrate that this
already very low SQL can be overcome using appropriately multimode squeezed
light. Benefitting from the large number of photons used in the experiment and
from the optimal choice of both the detection strategy and of the quantum
resource, the proposed scheme represents a significant potential improvement in
space-time positioning
Quantum-limited position measurements of a dark matter-wave soliton
We show that the position of a dark matter-wave soliton can be determined
with a precision that scales with the atomic density as . This
surpasses the standard shot-noise detection limit for independent particles,
without use of squeezing and entanglement, and it suggests that interactions
among particles may present new advantages in high-precision metrology. We also
take into account quantum density fluctuations due to phonon and Goldstone
modes and we show that they, somewhat unexpectedly, actually improve the
resolution. This happens because the fluctuations depend on the soliton
position and make a larger amount of information available.Comment: RevTex4, 5 pages, 1 figur
Soft clustering analysis of galaxy morphologies: A worked example with SDSS
Context: The huge and still rapidly growing amount of galaxies in modern sky
surveys raises the need of an automated and objective classification method.
Unsupervised learning algorithms are of particular interest, since they
discover classes automatically. Aims: We briefly discuss the pitfalls of
oversimplified classification methods and outline an alternative approach
called "clustering analysis". Methods: We categorise different classification
methods according to their capabilities. Based on this categorisation, we
present a probabilistic classification algorithm that automatically detects the
optimal classes preferred by the data. We explore the reliability of this
algorithm in systematic tests. Using a small sample of bright galaxies from the
SDSS, we demonstrate the performance of this algorithm in practice. We are able
to disentangle the problems of classification and parametrisation of galaxy
morphologies in this case. Results: We give physical arguments that a
probabilistic classification scheme is necessary. The algorithm we present
produces reasonable morphological classes and object-to-class assignments
without any prior assumptions. Conclusions: There are sophisticated automated
classification algorithms that meet all necessary requirements, but a lot of
work is still needed on the interpretation of the results.Comment: 18 pages, 19 figures, 2 tables, submitted to A
Optimal filter approximation by means of a phase-only filter with quantization
Approximate filters based on a phase-only filter for reliable recognition of objects are proposed. Good light efficiency and discrimination capability close to that of the optimal filter can be obtained. Computer simulation results are presented and discussed
Analysis of two-point statistics of cosmic shear: II. Optimizing the survey geometry
We present simulations of a cosmic shear survey and show how the survey
geometry influences the accuracy of determination of cosmological parameters.
We numerically calculate the full covariance matrices Cov of two-point
statistics of cosmic shear, based on the expressions derived in the first paper
of this series. The individual terms are compared for two survey geometries
with large and small cosmic variance. We use analyses based on maximum
likelihood of Cov and the Fisher information matrix in order to derive expected
constraints on cosmological parameters. As an illustrative example, we simulate
various survey geometries consisting of 300 individual fields of 13'x13' size,
placed (semi-)randomly into patches which are assumed to be widely separated on
the sky and therefore uncorrelated. Using the aperture mass statistics, the
optimum survey consists of 10 patches with 30 images in each patch. If
\Omega_m, \sigma_8 and \Gamma are supposed to be extracted from the data, the
minimum variance bounds on these three parameters are 0.17, 0.25 and 0.04
respectively. These variances raise slightly when the initial power spectrum
index n_s is also to be determined from the data. The cosmological constant is
only poorly constrained.Comment: 13 pages, 11 figures, Appeared in A&A, 2004. Typos corrected and
minor changes made to match the published versio
Quantum light depolarization: the phase-space perspective
Quantum light depolarization is handled through a master equation obtained by
coupling dispersively the field to a randomly distributed atomic reservoir.
This master equation is solved by transforming it into a quasiprobability
distribution in phase space and the quasiclassical limit is investigated.Comment: 6 pages, no figures. Submitted for publicatio
Measuring the dark side (with weak lensing)
We introduce a convenient parametrization of dark energy models that is
general enough to include several modified gravity models and generalized forms
of dark energy. In particular we take into account the linear perturbation
growth factor, the anisotropic stress and the modified Poisson equation. We
discuss the sensitivity of large scale weak lensing surveys like the proposed
DUNE satellite to these parameters. We find that a large-scale weak-lensing
tomographic survey is able to easily distinguish the Dvali-Gabadadze-Porrati
model from LCDM and to determine the perturbation growth index to an absolute
error of 0.02-0.03.Comment: 19 pages, 11 figure
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