47,629 research outputs found
Products of Random Matrices
We derive analytic expressions for infinite products of random 2x2 matrices.
The determinant of the target matrix is log-normally distributed, whereas the
remainder is a surprisingly complicated function of a parameter characterizing
the norm of the matrix and a parameter characterizing its skewness. The
distribution may have importance as an uncommitted prior in statistical image
analysis.Comment: 9 pages, 1 figur
The WIYN Open Cluster Study Photometric Binary Survey: Initial Findings for NGC 188
The WIYN open cluster study (WOCS) has been working to yield precise
magnitudes in the Johnson-Kron-Cousins UBVRI system for all stars in the field
of a selection of ``prototypical'' open clusters. Additionally, WOCS is using
radial velocities to obtain orbit solutions for all cluster binary stars with
periods of less than 1000 days. Recently, WOCS is being expanded to include the
near-infrared JHK_s (deep ground-based plus 2MASS) and mid-infrared ([3.6],
[4.5], [5.8], [8.0]) photometry from Spitzer/IRAC observations. This
multi-wavelength data (0.3--8.0 microns) allows us photometrically to identify
binaries, with mass ratios from 1.0--0.3, across a wide range of primary
masses. The spectral energy distribution (SED) fitter by Robitaille et al.
(2007) is used to fit the fluxes of 10--12 bands, converted from the observed
magnitudes, to Kurucz stellar models. Using this photometric technique, we find
that NGC 188 has a binary fraction of 36--49% and provide a star-by-star
comparison to the WOCS radial velocity-based binary study.Comment: 2 pages, 2 figures, Conference Proceedings from "Dynamical Evolution
of Dense Stellar Systems'', IAU Symposium 246, Eds. E. Vesperini, M. Giersz,
& A. Sill
Direct Characterization of Quantum Dynamics
The characterization of quantum dynamics is a fundamental and central task in
quantum mechanics. This task is typically addressed by quantum process
tomography (QPT). Here we present an alternative "direct characterization of
quantum dynamics" (DCQD) algorithm. In contrast to all known QPT methods, this
algorithm relies on error-detection techniques and does not require any quantum
state tomography. We illustrate that, by construction, the DCQD algorithm can
be applied to the task of obtaining partial information about quantum dynamics.
Furthermore, we argue that the DCQD algorithm is experimentally implementable
in a variety of prominent quantum information processing systems, and show how
it can be realized in photonic systems with present day technology.Comment: 4 pages, 2 figures, published versio
The trumping relation and the structure of the bipartite entangled states
The majorization relation has been shown to be useful in classifying which
transformations of jointly held quantum states are possible using local
operations and classical communication. In some cases, a direct transformation
between two states is not possible, but it becomes possible in the presence of
another state (known as a catalyst); this situation is described mathematically
by the trumping relation, an extension of majorization. The structure of the
trumping relation is not nearly as well understood as that of majorization. We
give an introduction to this subject and derive some new results. Most notably,
we show that the dimension of the required catalyst is in general unbounded;
there is no integer such that it suffices to consider catalysts of
dimension or less in determining which states can be catalyzed into a given
state. We also show that almost all bipartite entangled states are potentially
useful as catalysts.Comment: 7 pages, RevTe
Novel schemes for measurement-based quantum computation
We establish a framework which allows one to construct novel schemes for
measurement-based quantum computation. The technique further develops tools
from many-body physics - based on finitely correlated or projected entangled
pair states - to go beyond the cluster-state based one-way computer. We
identify resource states that are radically different from the cluster state,
in that they exhibit non-vanishing correlation functions, can partly be
prepared using gates with non-maximal entangling power, or have very different
local entanglement properties. In the computational models, the randomness is
compensated in a different manner. It is shown that there exist resource states
which are locally arbitrarily close to a pure state. Finally, we comment on the
possibility of tailoring computational models to specific physical systems as,
e.g. cold atoms in optical lattices.Comment: 5 pages RevTeX, 1 figure, many diagrams. Title changed, presentation
improved, material adde
Follow up on the crystal growth experiments of the LDEF
The results of the 4 solution growth experiments on the LDEF have been published elsewhere. Both the crystals of CaCO3, which were large and well shaped, and the much smaller TTF-TCNQ crystals showed unusual morphological behavior. The follow up on these experiments was begun in 1981, when ESA initiated a 'Concept Definition Study' on a large, 150 kg, Solution Growth Facility (SGF) to be included in the payload of EURECA-1, the European Retrievable Carrier. This carrier was a continuation of the European Spacelab and at that time planned for launch in 1987. The long delay of the LDEF retrieval and of subsequent missions brought about reflections both on the concept of crystal growth in space and on the choice of crystallization materials that had been made for the LDEF. Already before the LDEF retrieval, research on TTF-TCNQ had been stopped, and a planned growth experiment with TTF-TCNQ on the SGF/EURECA had been cancelled. The target of the SGF investigation is now more fundamental in nature. None of the crystals to be grown here are, like TTF-TCNQ, in particular demand by science or industry, and the crystals only serve the purpose of model crystals. The real purpose of the investigation is to study the growth behavior. One of the experiments, the Soret Coefficient Measurement experiment is not growing crystals at all, but has it as its sole purpose to obtain accurate information on thermal diffusion, a process of importance in crystal growth from solution
Useful entanglement can be extracted from all nonseparable states
We consider entanglement distillation from a single-copy of a multipartite
state, and instead of rates we analyze the "quality" of the distilled
entanglement. This "quality" is quantified by the fidelity with the GHZ-state.
We show that each not fully-separable state can increase the "quality"
of the entanglement distilled from other states, no matter how weakly entangled
is . We also generalize this to the case where the goal is distilling
states different than the GHZ. These results provide new insights on the
geometry of the set of separable states and its dual (the set of entanglement
witnesses).Comment: 7 page
Optimality of programmable quantum measurements
We prove that for a programmable measurement device that approximates every
POVM with an error , the dimension of the program space has to grow
at least polynomially with . In the case of qubits we can
improve the general result by showing a linear growth. This proves the
optimality of the programmable measurement devices recently designed in [G. M.
D'Ariano and P. Perinotti, Phys. Rev. Lett. \textbf{94}, 090401 (2005)]
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