Navegando por Autor "Aolita, Leandro"

Agora exibindo 1 - 4 de 4

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/0000-0001-8493-4019
The 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 dynamics
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, Alessandro
The 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 correction
Experimental Connection between the Instrumental and Bell Inequalities
(Multidisciplinary Digital Publishing, 2019-07-18) Agresti, Iris; Carvacho, Gonzalo; Poderini, Davide; Aolita, Leandro; Araújo, Rafael Chaves Souto; Sciarrino, Fabio
An investigated process can be studied in terms of the causal relations among the involved variables, representing it as a causal model. Some causal models are particularly relevant, since they can be tested through mathematical constraints between the joint probability distributions of the observables. This is a valuable tool because, if some data violates the constraints of a causal model, the implication is that the observed statistics is not compatible with that causal structure. Strikingly, when non-classical correlations come to play, a discrepancy between classical and quantum causal predictions can arise, producing a quantum violation of the classical causal constraints. The simplest scenario admitting such quantum violation is given by the instrumental causal processes. Here, we experimentally violate an instrumental test on a photonic platform and show how the quantum correlations violating the CHSH inequality can be mapped into correlations violating an instrumental test, despite the different forms of non-locality they display. Indeed, starting from a Bell-like scenario, we recover the violation of the instrumental scenario through a map between the two behaviours, which includes a post-selection of data and then we test an alternative way to violate the CHSH inequality, adopting the instrumental process platform
Experimental device-independent certified randomness generation with an instrumental causal structure
(Nature Research, 2020-06-18) Agresti, Iris; Poderini, Davide; Guerini, Leonardo; Mancusi, Michele; Carvacho, Gonzalo; Aolita, Leandro; Cavalcanti, Daniel; Araújo, Rafael Chaves Souto; Sciarrino, Fábio
The intrinsic random nature of quantum physics offers novel tools for the generation of random numbers, a central challenge for a plethora of fields. Bell non-local correlations obtained by measurements on entangled states allow for the generation of bit strings whose randomness is guaranteed in a device-independent manner, i.e. without assumptions on the measurement and state-generation devices. Here, we generate this strong form of certified randomness on a new platform: the so-called instrumental scenario, which is central to the field of causal inference. First, we theoretically show that certified random bits, private against general quantum adversaries, can be extracted exploiting device-independent quantum instrumental-inequality violations. Then, we experimentally implement the corresponding randomness-generation protocol using entangled photons and active feed-forward of information. Moreover, we show that, for low levels of noise, our protocol offers an advantage over the simplest Bell-nonlocality protocol based on the Clauser-Horn-Shimony- Holt inequality

SIGAA

Navegando por Autor "Aolita, Leandro"