Navegando por Autor "Cavalcanti, Daniel"

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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, Antonio
We 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 configuration
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
Efficient and operational quantifier of nondivisibility in terms of channel discrimination
(Physical Review A, 2025-02-04) Nery, Ranieri Vieira; Bernardes, Nadja Kolb; Cavalcanti, Daniel; Araújo, Rafael Chaves Souto; Duarte, Cristhiano
The understanding of open quantum systems is crucial for the development of quantum technologies. Of particular relevance is the characterization of divisible quantum dynamics, seen as a generalization of Markovian processes to the quantum setting. Here, we propose a way to detect divisibility and quantify how nondivisible a quantum channel is through the concept of channel discrimination. We ask how well we can distinguish generic dynamics from divisible dynamics. We show that this question can be answered efficiently through semidefinite programming, which provides us with an operational and efficient way to quantify nondivisibility
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 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
Satellite-based photonic quantum networks are small-world
(PRX Quantum, 2021-01-08) Araújo, Rafael Chaves Souto; Canabarro, Askery; Cavalcanti, Daniel; Brito, Samuraí Gomes de Aguiar
Recent milestone experiments establishing satellite-to-ground quantum communication are paving the way for the development of the quantum Internet, a network interconnected by quantum channels. Here, we employ network theory to study the properties of the photonic networks that can be generated by satellite-based quantum communication and compare them with those of their optical-fiber counterpart. We predict that satellites can generate small-world networks, implying that physically distant nodes are actually near from a network perspective. We also analyze the connectivity properties of the network and show, in particular, that they are robust against random failures. This positions satellite-based quantum communication as the most promising technology to distribute entanglement across large distances in quantum networks of growing size and complexity
Statistical properties of the quantum internet
(American Physical Society, 2020-05-27) Brito, Samuraí Gomes de Aguiar; Silva, Askery Alexandre Canabarro Barbosa da; Araújo, Rafael Chaves Souto; Cavalcanti, Daniel
Steady technological advances are paving the way for the implementation of the quantum internet, a network of locations interconnected by quantum channels. Here we propose a model to simulate a quantum internet based on optical fibers and employ network-theory techniques to characterize the statistical properties of the photonic networks it generates. Our model predicts a continuous phase transition between a disconnected and a highly connected phase and that the typical photonic networks do not present the small world property. We compute the critical exponents characterizing the phase transition, provide quantitative estimates for the minimum density of nodes needed to have a fully connected network and for the average distance between nodes. Our results thus provide quantitative benchmarks for the development of a quantum internet

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Navegando por Autor "Cavalcanti, Daniel"