42,190 research outputs found
Coarse-grained entanglement classification through orthogonal arrays
Classification of entanglement in multipartite quantum systems is an open
problem solved so far only for bipartite systems and for systems composed of
three and four qubits. We propose here a coarse-grained classification of
entanglement in systems consisting of subsystems with an arbitrary number
of internal levels each, based on properties of orthogonal arrays with
columns. In particular, we investigate in detail a subset of highly entangled
pure states which contains all states defining maximum distance separable
codes. To illustrate the methods presented, we analyze systems of four and five
qubits, as well as heterogeneous tripartite systems consisting of two qubits
and one qutrit or one qubit and two qutrits.Comment: 38 pages, 1 figur
Aberration in qualitative multilevel designs
Generalized Word Length Pattern (GWLP) is an important and widely-used tool
for comparing fractional factorial designs. We consider qualitative factors,
and we code their levels using the roots of the unity. We write the GWLP of a
fraction using the polynomial indicator function, whose
coefficients encode many properties of the fraction. We show that the
coefficient of a simple or interaction term can be written using the counts of
its levels. This apparently simple remark leads to major consequence, including
a convolution formula for the counts. We also show that the mean aberration of
a term over the permutation of its levels provides a connection with the
variance of the level counts. Moreover, using mean aberrations for symmetric
designs with prime, we derive a new formula for computing the GWLP of
. It is computationally easy, does not use complex numbers and
also provides a clear way to interpret the GWLP. As case studies, we consider
non-isomorphic orthogonal arrays that have the same GWLP. The different
distributions of the mean aberrations suggest that they could be used as a
further tool to discriminate between fractions.Comment: 16 pages, 1 figur
Commutative association schemes
Association schemes were originally introduced by Bose and his co-workers in
the design of statistical experiments. Since that point of inception, the
concept has proved useful in the study of group actions, in algebraic graph
theory, in algebraic coding theory, and in areas as far afield as knot theory
and numerical integration. This branch of the theory, viewed in this collection
of surveys as the "commutative case," has seen significant activity in the last
few decades. The goal of the present survey is to discuss the most important
new developments in several directions, including Gelfand pairs, cometric
association schemes, Delsarte Theory, spin models and the semidefinite
programming technique. The narrative follows a thread through this list of
topics, this being the contrast between combinatorial symmetry and
group-theoretic symmetry, culminating in Schrijver's SDP bound for binary codes
(based on group actions) and its connection to the Terwilliger algebra (based
on combinatorial symmetry). We propose this new role of the Terwilliger algebra
in Delsarte Theory as a central topic for future work.Comment: 36 page
Fresnel Interferometric Imager: ground-based prototype
The Fresnel Interferometric Imager is a space-based astronomical telescope
project yielding milli-arc second angular resolution and high contrast images
with loose manufacturing constraints. This optical concept involves diffractive
focusing and formation flying: a first "primary optics" space module holds a
large binary Fresnel Array, and a second "focal module" holds optical elements
and focal instruments that allow for chromatic dispersion correction.
We have designed a reduced-size Fresnel Interferometric Imager prototype and
made optical tests in our lab, in order to validate the concept for future
space missions. The Primary module of this prototype consists of a square, 8 cm
side, 23 m focal length Fresnel array. The focal module is composed of a
diaphragmed small telescope used as "field lens", a small cophased diverging
Fresnel Zone Lens (FZL) that cancels the dispersion and a detector. An
additional module collimates the artificial targets of various shapes, sizes
and dynamic ranges to be imaged.
In this paper, we describe the experimental setup, different designs of the
primary Fresnel array, and the cophased Fresnel Zone Lens that achieves
rigorous chromatic correction. We give quantitative measurements of the
diffraction limited performances and dynamic range on double sources. The tests
have been performed in the visible domain, lambda = 400 - 700 nm.
In addition, we present computer simulations of the prototype optics based on
Fresnel propagation, that corroborate the optical tests. This numerical tool
has been used to simulate the large aperture Fresnel arrays that could be sent
to space with diameters of 3 to 30 m, foreseen to operate from Lyman-alpha (121
nm) to mid I.R. (25 microns).Comment: 10 pages, 13 figures; accepted for publication in Applied Optic
Orthogonal methods based ant colony search for solving continuous optimization problems
Research into ant colony algorithms for solving continuous optimization problems forms one of the most
significant and promising areas in swarm computation. Although traditional ant algorithms are designed for combinatorial
optimization, they have shown great potential in solving a wide range of optimization problems, including continuous
optimization. Aimed at solving continuous problems effectively, this paper develops a novel ant algorithm termed "continuous orthogonal ant colony" (COAC), whose pheromone deposit mechanisms would enable ants to search for
solutions collaboratively and effectively. By using the orthogonal design method, ants in the feasible domain can explore
their chosen regions rapidly and e±ciently. By implementing an "adaptive regional radius" method, the proposed
algorithm can reduce the probability of being trapped in local optima and therefore enhance the global search capability and accuracy. An elitist strategy is also employed to reserve the most valuable points. The performance of the COAC is
compared with two other ant algorithms for continuous optimization of API and CACO by testing seventeen functions
in the continuous domain. The results demonstrate that the proposed COAC algorithm outperforms the others
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