Navegando por Autor "Acín, Antonio"
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Artigo Bounding the sets of classical and quantum correlations in networks(American Physical Society, 2019-10-03) Pozas-Kerstjens, Alejandro; Rabelo, Rafael; Rudnicki, Łukasz; Araújo, Rafael Chaves Souto; Cavalcanti, Daniel; Navascu´es, Miguel; Acín, AntonioWe present a method that allows the study of classical and quantum correlations in networks with causally independent parties, such as the scenario underlying entanglement swapping. By imposing relaxations of factorization constraints in a form compatible with semidefinite programing, it enables the use of the Navascu´es-Pironio-Acín hierarchy in complex quantum networks. We first show how the technique successfully identifies correlations not attainable in the entanglement-swapping scenario. Then we use it to show how the nonlocal power of measurements can be activated in a network: there exist measuring devices that, despite being unable to generate nonlocal correlations in the standard Bell scenario, provide a classical-quantum separation in an entanglement swapping configurationArtigo Detecting nonlocality of noisy multipartite states with the Clauser-Horne-Shimony-Holt inequality(Physical Review A, 2014-04-14) Araújo, Rafael Chaves Souto; Acín, Antonio; Aolita, Leandro; Cavalcanti, Daniel; https://orcid.org/0000-0001-8493-4019The Clauser-Horne-Shimony-Holt inequality was originally proposed as a Bell inequality to detect nonlocality in bipartite systems. However, it can also be used to certify the nonlocality of multipartite quantum states. We apply this to study the nonlocality of multipartite Greenberger-Horne-Zeilinger (GHZ), W, and graph states under local decoherence processes. We derive lower bounds on the critical local-noise strength tolerated by the states before becoming local. In addition, for the whole noisy dynamics, we derive lower bounds on the corresponding nonlocal content for the three classes of states. All the bounds presented can be calculated efficiently and, in some cases, provide significantly tighter estimates than with any other known method. For example, they reveal that 𝑁-qubit GHZ states undergoing local dephasing are, for all 𝑁, nonlocal throughout all the dephasing dynamicsArtigo Nonlocality in sequential correlation scenarios(New Journal of Physics, 2014-03-28) Gallego, Rodrigo; Würflinge, Lars Erik; Araújo, Rafael Chaves Souto; Acín, Antonio; Navascués, MiguelAs first shown by Popescu (1995 Phys. Rev. Lett. 74 2619), some quantum states only reveal their nonlocality when subjected to a sequence of measurements while giving rise to local correlations in standard Bell tests. Motivated by this manifestation of 'hidden nonlocality' we set out to develop a general framework for the study of nonlocality when sequences of measurements are performed. Similar to Gallego et al (2013 Phys. Rev. Lett. 109 070401) our approach is operational, i.e. the task is to identify the set of allowed operations in sequential correlation scenarios and define nonlocality as the resource that cannot be created by these operations. This leads to a characterization of sequential nonlocality that contains as particular cases standard nonlocality and hidden nonlocality