1,771 research outputs found
Hierarchy of efficiently computable and faithful lower bounds to quantum discord
Quantum discord expresses a fundamental non-classicality of correlations more
general than quantum entanglement. We combine the no-local-broadcasting
theorem, semidefinite-programming characterizations of quantum fidelity and
quantum separability, and a recent breakthrough result of Fawzi and Renner
about quantum Markov chains to provide a hierarchy of computationally efficient
lower bounds to quantum discord. Such a hierarchy converges to the surprisal of
measurement recoverability introduced by Seshadreesan and Wilde, and provides a
faithful lower bound to quantum discord already at the lowest non-trivial
level. Furthermore, the latter constitutes by itself a valid discord-like
measure of the quantumness of correlations.Comment: 7 pages, 2 figures; comments -- also about "extendable" Vs
"extendible" -- welcom
The problem with the geometric discord
We argue that the geometric discord introduced in [B. Dakic, V. Vedral, and
C. Brukner, Phys. Rev. Lett. 105, 190502 (2010)] is not a good measure for the
quantumness of correlations, as it can increase even under trivial local
reversible operations of the party whose classicality/non-classicality is not
tested. On the other hand it is known that the standard, mutual-information
based discord does not suffer this problem; a simplified proof of such a fact
is given.Comment: 5 pages. Changes in ver 2: typos corrected, added short proof of
monotonicity of standard quantum discord under one-side action. This note is
meant to stimulate discussion in the community: comments are welcom
Einstein-Podolsky-Rosen steering provides the advantage in entanglement-assisted subchannel discrimination with one-way measurements
Steering is the entanglement-based quantum effect that embodies the "spooky
action at a distance" disliked by Einstein and scrutinized by Einstein,
Podolsky, and Rosen. Here we provide a necessary and sufficient
characterization of steering, based on a quantum information processing task:
the discrimination of branches in a quantum evolution, which we dub subchannel
discrimination. We prove that, for any bipartite steerable state, there are
instances of the quantum subchannel discrimination problem for which this state
allows a correct discrimination with strictly higher probability than in
absence of entanglement, even when measurements are restricted to local
measurements aided by one-way communication. On the other hand, unsteerable
states are useless in such conditions, even when entangled. We also prove that
the above steering advantage can be exactly quantified in terms of the steering
robustness, which is a natural measure of the steerability exhibited by the
state.Comment: 10 pages, 2 figures, comments welcom
Improved entropic uncertainty relations and information exclusion relations
The uncertainty principle can be expressed in entropic terms, also taking
into account the role of entanglement in reducing uncertainty. The information
exclusion principle bounds instead the correlations that can exist between the
outcomes of incompatible measurements on one physical system, and a second
reference system. We provide a more stringent formulation of both the
uncertainty principle and the information exclusion principle, with direct
applications for, e.g., the security analysis of quantum key distribution,
entanglement estimation, and quantum communication. We also highlight a
fundamental distinction between the complementarity of observables in terms of
uncertainty and in terms of information.Comment: 11 pages, 1 figure, v2: close to published versio
Antidumping and safeguard mechanisms : the Brazilian experience, 1988-2003
The authors focus on the evaluation of the antidumping regime from 1988 through 2003. During these years the Brazilian economy had to cope with several periods of macroeconomic instability and overvaluation of the domestic currency, particularly from 1990-92 and 1994-98. As a result, from 1992 through 1998, import volumes increased significantly. Although during these years, the demand for antidumping protection was growing, the number of investigations concluded with an affirmative determination was only 52 percent. The authors explain that the institutional framework in charge of administering the antidumping regime was subject to several reforms. Along this process, the Ministry of Development, Industry, and Trade saw its role strengthened. This ministry has a more protectionist bias than the Ministry of Finance that, during the initial years of the liberalization program, played a prominent role in decisions regarding antidumping investigations and measures. The authors conclude that in comparison with other countries that are important users of the antidumping mechanism, the Brazilian experience reveals two interesting features: 1) A relatively small rate of final positive determinations. 2) A tradition of applying antidumping duties in amounts that on average have been quite lower than the full dumping margins.TF054105-DONOR FUNDED OPERATION ADMINISTRATION FEE INCOME AND EXPENSE ACCOUNT,Economic Theory&Research,Environmental Economics&Policies,Trade Policy,Rules of Origin
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