Navegando por Autor "Lauand, Pedro"

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Estimating the volume of correlation sets in causal networks
(Physical Review A, 2024-01-24) Camillo, Giulio; Lauand, Pedro; Poderini, Davide; Rabelo, Rafael; Araújo, Rafael Chaves Souto
Causal networks beyond that in the paradigmatic Bell's theorem can lead to new kinds and applications of nonclassical behavior. Their study, however, has been hindered by the fact that they define a nonconvex set of correlations and only very incomplete or approximated descriptions have been obtained so far, even for the simplest scenarios. Here we take a different stance on the problem and consider the relative volume of classical or nonclassical correlations a given network gives rise to, considering distances to sets of interest and how they distribute too. Among other results, we show instances where the inflation technique, arguably the most disseminated tool in the community, is unable to detect a significant portion of the nonclassical behaviors, up to three copies of each source, and that a concentration phenomenon of distances happens in one of them. Interestingly, we also show that the use of interventions, a central tool in causal inference, can enhance substantially our ability to witness nonclassicality
Observational-interventional Bell inequalities
(Physical Review A, 2024-10-21) Poderini, Davide; Nery, Ranieri Vieira; Moreno Filho, Marcos George Magalhães; Zamora, Santiago; Lauand, Pedro; Araújo, Rafael Chaves Souto
Generalizations of Bell's theorem, particularly within quantum networks, are now being analyzed through the lens of causal inference. However, the exploration of interventions, a central concept in causality theory, remains significantly unexplored. In this work, we take an initial step in this direction, by analyzing the instrumental scenario and proposing hybrid Bell inequalities integrating observational and interventional data. Focusing on binary outcomes with any number of inputs, we obtain the complete characterization of the observational-interventional polytope, equivalent to a Hardy-like Bell inequality, albeit describing a distinct quantum experiment. To illustrate its applications, we show a significant enhancement regarding threshold detection efficiencies for quantum violations also showing the use of this hybrid approach in quantum steering scenarios
Witnessing nonclassicality in a causal structure with three observable variables
(PRX Quantum, 2023-04-20) Lauand, Pedro; Poderini, Davide; Nery, Ranieri Vieira; Moreno Filho, Marcos George Magalhães; Pollyceno, Lucas; Rabelo, Rafael; Araújo, Rafael Chaves Souto
Seen from the modern lens of causal inference, Bell’s theorem is nothing other than the proof that a specific classical causal model cannot explain quantum correlations. It is thus natural to move beyond Bell’s paradigmatic scenario and consider different causal structures. For the specific case of three observable variables, it is known that there are three nontrivial causal networks. Two of those are known to give rise to quantum nonclassicality: the instrumental and the triangle scenarios. Here we analyze the third and remaining one, which we name the Evans scenario, akin to the causal structure underlying the entanglement-swapping experiment. We prove a number of results about this elusive scenario and introduce new and efficient computational tools for its analysis that can also be adapted to deal with more general causal structures. We do not solve its main open problem—whether quantum nonclassical correlations can arise from it—but give a significant step in this direction by proving that postquantum correlations, analogous to the paradigmatic Popescu-Rohrlich box, do violate the constraints imposed by a classical description of the Evans causal structure

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Navegando por Autor "Lauand, Pedro"