6,369 research outputs found
Determination of maximal Gaussian entanglement achievable by feedback-controlled dynamics
We determine a general upper bound for the steady-state entanglement
achievable by continuous feedback for systems of any number of bosonic degrees
of freedom. We apply such a bound to the specific case of parametric
interactions - the most common practical way to generate entanglement in
quantum optics - and single out optimal feedback strategies that achieve the
maximal entanglement. We also consider the case of feedback schemes entirely
restricted to local operations and compare their performance to the optimal,
generally nonlocal, schemes.Comment: 4 pages. Published versio
Extremal extensions of entanglement witnesses: Unearthing new bound entangled states
In this paper, we discuss extremal extensions of entanglement witnesses based
on Choi's map. The constructions are based on a generalization of the Choi map
due to Osaka, from which we construct entanglement witnesses. These extremal
extensions are powerful in terms of their capacity to detect entanglement of
positive under partial transpose (PPT) entangled states and lead to unearthing
of entanglement of new PPT states. We also use the Cholesky-like decomposition
to construct entangled states which are revealed by these extremal entanglement
witnesses.Comment: 8 pages 6 figures revtex4-
Discrimination between pure states and mixed states
In this paper, we discuss the problem of determining whether a quantum system
is in a pure state, or in a mixed state. We apply two strategies to settle this
problem: the unambiguous discrimination and the maximum confidence
discrimination. We also proved that the optimal versions of both strategies are
equivalent. The efficiency of the discrimination is also analyzed. This scheme
also provides a method to estimate purity of quantum states, and Schmidt
numbers of composed systems
Entropic uncertainty relations and entanglement
We discuss the relationship between entropic uncertainty relations and
entanglement. We present two methods for deriving separability criteria in
terms of entropic uncertainty relations. Especially we show how any entropic
uncertainty relation on one part of the system results in a separability
condition on the composite system. We investigate the resulting criteria using
the Tsallis entropy for two and three qubits.Comment: 8 pages, 3 figures, v2: small change
Bounds on Multipartite Entangled Orthogonal State Discrimination Using Local Operations and Classical Communication
We show that entanglement guarantees difficulty in the discrimination of
orthogonal multipartite states locally. The number of pure states that can be
discriminated by local operations and classical communication is bounded by the
total dimension over the average entanglement. A similar, general condition is
also shown for pure and mixed states. These results offer a rare operational
interpretation for three abstractly defined distance like measures of
multipartite entanglement.Comment: 4 pages, 1 figure. Title changed in accordance with jounral request.
Major changes to the paper. Intro rewritten to make motivation clear, and
proofs rewritten to be clearer. Picture added for clarit
UV and X-ray Spectral Lines of FeXXIII Ion for Plasma Diagnostics
We have calculated X-ray and UV spectra of Be-like Fe (FeXXIII) ion in
collisional-radiative model including all fine-structure transitions among the
2s^2, 2s2p, 2p^2, 2snl, and 2pnl levels where n=3 and 4, adopting data for the
collision strengths by Zhang & Sampson (1992) and by Sampson, Goett, & Clark
(1984). Some line intensity ratios can be used for the temperature diagnostics.
We show 5 ratios in UV region and 9 ratios in X-ray region as a function of
electron temperature and density at 0.3keV < T_e < 10keV and . The effect of cascade in these line ratios and in the level
population densities are discussed.Comment: LaTeX, 18 pages, 10 Postscript figures. To appear in Physica Script
CHIANTI - an Atomic Database for Emission Lines. Paper VI: Proton Rates and Other Improvements
The CHIANTI atomic database contains atomic energy levels, wavelengths,
radiative transition probabilities and electron excitation data for a large
number of ions of astrophysical interest. Version 4 has been released, and
proton excitation data is now included, principally for ground configuration
levels that are close in energy. The fitting procedure for excitation data,
both electrons and protons, has been extended to allow 9 point spline fits in
addition to the previous 5 point spline fits. This allows higher quality fits
to data from close-coupling calculations where resonances can lead to
significant structure in the Maxwellian-averaged collision strengths. The
effects of photoexcitation and stimulated emission by a blackbody radiation
field in a spherical geometry on the level balance equations of the CHIANTI
ions can now be studied following modifications to the CHIANTI software. With
the addition of H I, He I and N I, the first neutral species have been added to
CHIANTI. Many updates to existing ion data-sets are described, while several
new ions have been added to the database, including Ar IV, Fe VI and Ni XXI.
The two-photon continuum is now included in the spectral synthesis routines,
and a new code for calculating the relativistic free-free continuum has been
added. The treatment of the free-bound continuum has also been updated.Comment: CHIANTI is available at http://wwwsolar.nrl.navy.mil/chianti.htm
Highly accurate calculations of the rotationally excited bound states in three-body systems
An effective optimization strategy has been developed to construct highly
accurate bound state wave functions in various three-body systems. Our
procedure appears to be very effective for computations of weakly bound states
and various excited states, including rotationally excited states, i.e. states
with . The efficiency of our procedure is illustrated by computations
of the excited states in the and muonic
molecular ions, states in the non-symmetric and
ions and and states in He atom(s)
Quantum Phase Transitions in Anti-ferromagnetic Planar Cubic Lattices
Motivated by its relation to an -hard problem, we analyze the
ground state properties of anti-ferromagnetic Ising-spin networks embedded on
planar cubic lattices, under the action of homogeneous transverse and
longitudinal magnetic fields. This model exhibits a quantum phase transition at
critical values of the magnetic field, which can be identified by the
entanglement behavior, as well as by a Majorization analysis. The scaling of
the entanglement in the critical region is in agreement with the area law,
indicating that even simple systems can support large amounts of quantum
correlations. We study the scaling behavior of low-lying energy gaps for a
restricted set of geometries, and find that even in this simplified case, it is
impossible to predict the asymptotic behavior, with the data allowing equally
good fits to exponential and power law decays. We can therefore, draw no
conclusion as to the algorithmic complexity of a quantum adiabatic ground-state
search for the system.Comment: 7 pages, 13 figures, final version (accepted for publication in PRA
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