Navegando por Autor "Ringbauer, Martin"
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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 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 effectArtigo Probing the non-classicality of temporal correlations(Verein zur Förderung des Open Access Publizierens in den Quantenwissenschaften, 2017-11-25) Ringbauer, Martin; Araújo, Rafael Chaves SoutoCorrelations between spacelike separated measurements on entangled quantum systems are stronger than any classical correlations and are at the heart of numerous quantum technologies. In practice, however, spacelike separation is often not guaranteed and we typically face situations where measurements have an underlying time order. Here we aim to provide a fair comparison of classical and quantum models of temporal correlations on a single particle, as well as timelike-separated correlations on multiple particles. We use a causal modeling approach to show, in theory and experiment, that quantum correlations outperform their classical counterpart when allowed equal, but limited communication resources. This provides a clearer picture of the role of quantum correlations in timelike separated scenarios, which play an important role in foundational and practical aspects of quantum information processing