Navegando por Autor "Fedrizzi, Alessandro"
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Artigo Enhanced multiqubit phase estimation in noisy environments by local encoding(American Physical Society, 2019-11-01) Proietti, Massimiliano; Ringbauer, Martin; Graffitti, Francesco; Barrow, Peter; Pickston, Alexander; Kundys, Dmytro; Cavalcanti, Daniel; Aolita, Leandro; Araújo, Rafael Chaves Souto; Fedrizzi, AlessandroThe first generation of multiqubit quantum technologies will consist of noisy, intermediate-scale devices for which active error correction remains out of reach. To exploit such devices, it is thus imperative to use passive error protection that meets a careful trade-off between noise protection and resource overhead. Here, we experimentally demonstrate that single-qubit encoding can significantly enhance the robustness of entanglement and coherence of four-qubit graph states against local noise with a preferred direction. In particular, we explicitly show that local encoding provides a significant practical advantage for phase estimation in noisy environments. This demonstrates the efficacy of local unitary encoding under realistic conditions, with potential applications in multiqubit quantum technologies for metrology, multipartite secrecy, and error correctionArtigo Entanglement-based quantum communication complexity beyond Bell nonlocality(npj Quantum Information, 2022-02-03) Ho, Joseph; Moreno Filho, Marcos George Magalhães; Brito, Samuraí Gomes de Aguiar; Graffitti, Francesco; Morrison, Christopher L.; Nery, Ranieri Vieira; Pickston, Alexander; Proietti, Massimiliano; Rabelo, Rafael; Fedrizzi, Alessandro; Araújo, Rafael Chaves SoutoEfficient distributed computing offers a scalable strategy for solving resource-demanding tasks, such as parallel computation and circuit optimisation. Crucially, the communication overhead introduced by the allotment process should be minimised—a key motivation behind the communication complexity problem (CCP). Quantum resources are well-suited to this task, offering clear strategies that can outperform classical counterparts. Furthermore, the connection between quantum CCPs and non-locality provides an information-theoretic insight into fundamental quantum mechanics. Here we connect quantum CCPs with a generalised non-locality framework—beyond Bell’s paradigmatic theorem—by incorporating the underlying causal structure, which governs the distributed task, into a so-called non-local hidden-variable model. We prove that a new class of communication complexity tasks can be associated with Bell-like inequalities, whose violation is both necessary and sufficient for a quantum gain. We experimentally implement a multipartite CCP akin to the guess-your-neighbour-input scenario, and demonstrate a quantum advantage when multipartite Greenberger-Horne-Zeilinger (GHZ) states are shared among three usersArtigo Experimental test of nonlocal causality(American Association for the Advancement of Science, 2016-08-16) Ringbauer, Martin; Giarmatzi, Christina; Araújo, Rafael Chaves Souto; Costa, Fabio; White, Andrew G.; Fedrizzi, AlessandroExplaining observations in terms of causes and effects is central to empirical science. However, correlations between entangled quantum particles seem to defy such an explanation. This implies that some of the fundamental assumptions of causal explanations have to give way. We consider a relaxation of one of these assumptions, Bell’s local causality, by allowing outcome dependence: a direct causal influence between the outcomes of measurements of remote parties. We use interventional data from a photonic experiment to bound the strength of this causal influence in a two-party Bell scenario, and observational data from a Bell-type inequality test for the considered models. Our results demonstrate the incompatibility of quantum mechanics with a broad class of nonlocal causal models, which includes Bell-local models as a special case. Recovering a classical causal picture of quantum correlations thus requires an even more radical modification of our classical notion of cause and effect