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