ECT - Artigos publicados em periódicos
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Artigo Design and experimental setup of an innovative tribometer aiming to evaluate small quantities of lubricants(Lubricants, 2025) Oliveira, Adilson José de; Silva, Lenine Marques de Castro; Rocha, Aylla Maria Alencar; Oliveira Junior, José Josemar de; Alves, Salete Martins; https://orcid.org/0000-0003-1272-0171; https://orcid.org/0000-0001-6104-569X; https://orcid.org/0000-0002-2659-4746The proposed tribometer design evaluates lubricants’ lubricating and wear protection properties at the interface of a loaded set of gears. However, this tribometer configuration and testing procedure described in standard ISO 14645-1 does not limit the tribological studiesof gear test rigs. This study aimed to design and manufacture a mechanical transmission test rig capable of investigating the tribological condition of a lubricated enclosed gears transmission. The methodology consisted of (i) a definition of the test rig’s requirements; (ii) downsizing the main subassemblies present in the ISO 14635-1 test rig; (iii) designing innovative subassemblies; (iv) an instrumentation and data acquisition system, and (v) setup testing. The proposed system is suitable for evaluating small quantities of lubricants, allowing the analysis of special lubricants such as nanolubricants and ionic liquids in development for gearbox applications. Also, the dynamic loading avoids interruption in the test, providing results closer to working conditions. The experimental test evaluated the lubrication ability of two different base oils simultaneously under various loading conditions. Also, monitoring vibration signals helped identify the appearance of damage on the gear surfaceArtigo A novel technology to deposition diamond-like carbon thin films: cathodic cylinder plasma deposition(JOM The Journal of The Minerals, Metals & Materials Society (TMS), 2025) Araújo, Anthunes Íkaro de; Nascimento, Igor Oliveira; Feitor, Michelle Cequeira; Libório, Maxwell Santana; Linhares, Álvaro Albueno da Silva; Vieira, Pâmela Samara; Alves, Salete Martins; Sousa, Rômulo Ribeiro Magalhães de; Lima, Cleânio da Luz; Sousa, Ediones Maciel de; Costa, Thercio Henrique de Carvalho; https://orcid.org/0009-0007-8181-7280; https://orcid.org/0000-0002-4850-9493; https://orcid.org/0000-0003-1579-8775; https://orcid.org/0009-0002-0627-0530; https://orcid.org/0000-0002-2659-4746; https://orcid.org/0000-0003-3958-7008This study investigates the influence of deposition temperature on the formation of diamond-Like carbon (DLC) films on AISI 4340 steel using the cathodic cylinder plasma deposition (CCyPD) technique. The films were deposited in an acetylene atmosphere at 350C, 400C, and 450C, and the samples were characterized using Raman spectroscopy, X-ray diffraction (XRD), Vickers hardness testing, and friction coefficient measurements. The results indicate that increasing the deposition temperature significantly impacts the microstructure and tribological properties of the DLC films. At 450C, the films exhibited higher hardness due to the increased concentration of sp3 carbon, which led to a denser and more rigid structure. However, a notable reduction in film thickness was observed, likely due to increased carbon deposition efficiency and structural densification. The film deposited at 400C demonstrated the optimal balance between hardness and wear resistance. These findings highlight the critical role of temperature control in optimizing the mechanical and tribological properties of DLC films for various industrial applicationsArtigo Development of nanostructured biogrease for wheel/rail contact application(Tribology International, 2026) Mello, Valdicleide Silva; Franceschini, Dante Ferreira; Scandian, Cherlio; Alves, Salete Martins; https://orcid.org/0000-0001-6413-6650; https://orcid.org/0000-0001-7328-6116; https://orcid.org/0000-0002-4393-719X; https://orcid.org/0000-0002-2659-4746This study aims to develop a sustainable grease using nanotechnology to increase its tribological performance in wheel/rail systems. This work consisted of two steps: first, grease production, with an innovative technique to add nanoparticles in the grease, and the second was a tribological test using a pin-on-disc tribometer. The tribological pair was extracted from the rail and wheel. Epoxidized soybean oil and natural nano-structured thickener were used to formulate biogrease. The results showed that this new grease could significantly reduce the wear on the wheel and rail compared to reference grease, avoiding oxidation of the worn surfaces. Also, adding nanoparticles can catalyze reactions on base oil, forming a tribofilm of carbon amorphousArtigo Erosion behavior of turbine blades due to sand and salt particles(Journal of Composite MaterialsOnlineFirst, 2025) Silva, Ranaildo Gomes da; Silveira, Pedro Lucas Gomes de Souza; Cunha, Rayane Dantas da; Souza, Luiz Guilherme Vieira Meira de; Alves, Salete Martins; https://orcid.org/0000-0003-0569-7719; https://orcid.org/0000-0002-2659-4746This study investigates the degradation of wind turbine blades (WTBs) exposed to the atmospheric conditions of tropical coastal environments. A wind tunnel experimental methodology was employed to simulate the erosive effects of airborne particulates, focusing on the influence of salt and sand particles. Specimens were subjected to controlled wind speeds and impact angles to assess material wear mechanisms. The results indicated that a 45° impact angle led to increased material loss due to both normal and tangential impact components. The highest mass loss recorded was 0.78% in the salt and sand particles test, while the most significant increase in surface roughness was 1.89 µm at a 90° impact angle, confirming the severe impact of perpendicular erosion. SEM analysis revealed that fiberglass delamination contributed to the degradation process, particularly in high-impact scenarios. These findings provide insights into material behavior under extreme coastal conditions and emphasize the need for improved protective coatings and maintenance strategies for WTBs in tropical maritime regionsArtigo Tribological behaviour of Cuo@Rgo nanoparticles under different slide‑to‑roll(Tribology Letters, 2025) Alves, Salete Martins; Cunha, R. D.; Morina, Ardian; https://orcid.org/0000-0002-2659-4746; https://orcid.org/0000-0001-8868-2664This paper aims to develop core–shell nanoparticles by combining CuO (core) and reduced graphene oxide (shell) as lubricant additives and understand their action under different slide-to-roll ratios. The SRRs evaluated were 50 and 200%, with nanoparticles concentrations of 0.05 and 0.1wt%. The worn tracks were characterized through WLI, SEM, TEM and Raman Spectroscopy. The results showed that the lubrication mechanism and tribofilm formation are strongly associated with the type of contact. At SRR 200%, nanolubricant reduced friction and wear; it was observed exfoliation of nanoparticles, the CuO acted as rolling, and the rGO sheet was deposited on a worn surface. On the other hand, for SRR 50% doesn´t decrease the friction coefficient; however, a thicker tribofilm was produced with nanoparticlesArtigo Quantifying causal influences in the presence of a quantum common cause(Physical Review Letters, 2020-12-02) Araújo, Rafael Chaves Souto; Miklin, Nikolai; Gachechiladze, MariamiQuantum mechanics challenges our intuition on the cause-effect relations in nature. Some fundamental concepts, including Reichenbach’s common cause principle or the notion of local realism, have to be reconsidered. Traditionally, this is witnessed by the violation of a Bell inequality. But are Bell inequalities the only signature of the incompatibility between quantum correlations and causality theory? Motivated by this question, we introduce a general framework able to estimate causal influences between two variables, without the need of interventions and irrespectively of the classical, quantum, or even postquantum nature of a common cause. In particular, by considering the simplest instrumental scenario—for which violation of Bell inequalities is not possible—we show that every pure bipartite entangled state violates the classical bounds on causal influence, thus, answering in negative to the posed question and opening a new venue to explore the role of causality within quantum theoryArtigo 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/0000-0001-8493-4019The 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 dynamicsArtigo Device-independent witness for the nonobjectivity of quantum dynamics(Physical Review A, 2023-09-05) Araújo, Rafael Chaves Souto; Rodari, Giovanni; Moreno Filho, Marcos George Magalhães; Polino, Emanuele; Nery, Ranieri Vieira; Suprano, Alessia; Duarte, Cristhiano; Sciarrino, Fabio; Poderini, DavideQuantum Darwinism offers an explanation for the emergence of classical objective features (those we are used to at macroscopic scales) from quantum properties at the microscopic level. The interaction of a quantum system with its surroundings redundantly proliferates information to many parts of the environment, turning it accessible and objective to different observers. However, given that one cannot probe the quantum system directly, only its environment, how to determine whether an unknown quantum property can be deemed objective? Here we propose a probabilistic framework to analyze this question and show that objectivity implies a Bell-like inequality. Among several other results, we show quantum violations of this inequality, a device-independent proof of the nonobjectivity of quantum correlations. We also implement a photonic experiment where the temporal degree of freedom of photons is the quantum system of interest, while their polarization acts as the environment. Employing a fully black-box approach, we achieve the violation of a Bell-like inequality, thus certifying the nonobjectivity of the underlying quantum dynamics in a fully device-independent frameworkArtigo Quantum Markov monogamy inequalities(Physical Review A, 2022-08-29) Araújo, Rafael Chaves Souto; Céleri, Lucas Chibebe; Capela, Matheus; Modi, KavanMarkovianity lies at the heart of communication problems. This in turn makes the information-theoretic characterization of Markov processes worthwhile. Data-processing inequalities are ubiquitous in this sense, assigning necessary conditions for all Markov processes. We address here the problem of the information-theoretic analysis of constraints on Markov processes in the quantum regime. We show the existence of a class of quantum data-processing inequalities called here quantum Markov monogamy inequalities. This class of necessary conditions on quantum Markov processes is inspired by its counterpart for classical Markov processes, thus providing a strong link between classical and quantum constraints on Markovianity. We go on to construct a family of multitime quantum Markov monogamy inequalities, based on the process tensor formalism and that exploits multitime correlations. We then show, by means of an explicit example, that the Markov monogamy inequalities can be stronger than the usual quantum data-processing inequalitiesArtigo Experimental genuine tripartite nonlocality in a quantum triangle network(PRX Quantum, 2022-09-21) Araújo, Rafael Chaves Souto; Poderini, Davide; Polino, Emanuele; Agresti, Iris; Vera, Gonzalo Alfredo Carvacho; Canabarro, Askery; Wolfe, Elie; Suprano, Alessia; Sciarrino, FabioQuantum networks are the center of many of the recent advances in quantum science, not only leading to the discovery of new properties in the foundations of quantum theory but also allowing for novel communication and cryptography protocols. It is known that networks beyond that in the paradigmatic Bell’s theorem imply new and sometimes stronger forms of nonclassicality. Due to a number of practical difficulties, however, the experimental implementation of such networks remains far less explored. Going beyond what has been previously tested, here we verify the nonlocality of an experimental triangle network, consisting of three independent sources of bipartite entangled photon states interconnecting three distant parties. By performing separable measurements only and evaluating parallel chained Bell inequalities, we show that such networks can lead to a genuine form of tripartite nonlocality, where classical models are unable to mimic the quantum predictions even if some of the parties are allowed to communicateArtigo 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 AguiarRecent 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 complexityArtigo Semi-device-independent certification of entanglement in superdense coding(Physical Review A, 2021-02-25) Araújo, Rafael Chaves Souto; Nery, Ranieri Vieira; Gois, Carlos de; Rabelo, Rafael; Marcos George Magalhães Moreno FilhoSuperdense coding is a paradigmatic protocol in quantum information science, employing a quantum communication channel to send classical information more efficiently. As we show here, it can be understood as a particular case of a prepare and measure experiment, a scenario that has attracted growing attention for its fundamental and practical applications. Formulating superdense coding as a prepare and measure scenario allows us to provide a semi-device-independent witness of entanglement that significantly improves over previous tests. Furthermore, we also show how to adapt our results into self-testing of maximally entangled states and also provide a semidefinite program formulation allowing one to efficiently optimize, for any shared quantum state, the probability of success in the superdense coding protocolArtigo General Method for Classicality Certification in the Prepare and Measure Scenario(PRX Quantum, 2021-07-20) Araújo, Rafael Chaves Souto; Moreno Filho, Marcos George Magalhães; Nery, Ranieri Vieira; Brito, Samuraí Gomes de Aguiar; Gois, Carlos de; Rabelo, RafaelPreparing and measuring physical systems are the operational building blocks of any physical experiment, and to describe them is the first purpose of any physical theory. Remarkably, even when only uncharacterized preparation and measurement devices are present, it is sometimes possible to distinguish between the behaviors of quantum and classical systems from only observational data. Certifying the physical origin of measurement statistics in the prepare and measure scenario is of primal importance for developing quantum networks, distributing quantum keys, and certifying randomness, to mention a few applications, but, surprisingly, no general methods to do so are known. We progress on this problem by crafting a general, sufficient condition to certify that a given set of preparations can only generate classical statistics, for any number of generalized measurements. As an application, we employ the method to demonstrate nonclassicality activation in the prepare and measure scenario, also considering its application in random access codes. Following that, we adapt our method to certify, again through a sufficient condition, whether a given set of measurements can never give rise to nonclassical behaviors, irrespective of what preparations they may act upon. This, in turn, allows us to find a large set of incompatible measurements that cannot be used to demonstrate nonclassicality, thus showing incompatibility is not sufficient for nonclassicality in the prepare and measure scenario.Artigo Causal Networks and Freedom of Choice in Bell’s Theorem(PRX Quantum, 2021-11-03) Araújo, Rafael Chaves Souto; Moreno Filho, Marcos George Magalhães; Polino, Emanuele; Poderini, Davide; Agresti, Iris; Suprano, Alessia; Barros, Mariana Rodrigues; Carvacho, Gonzalo; Wolfe, Elie; Canabarro, Askery; Spekkens, Robert W.; Sciarrino, FabioBell’s theorem is typically understood as the proof that quantum theory is incompatible with local-hidden-variable models. More generally, we can see the violation of a Bell inequality as witnessing the impossibility of explaining quantum correlations with classical causal models. The violation of a Bell inequality, however, does not exclude classical models where some level of measurement dependence is allowed, that is, the choice made by observers can be correlated with the source generating the systems to be measured. Here, we show that the level of measurement dependence can be quantitatively upper bounded if we arrange the Bell test within a network. Furthermore, we also prove that these results can be adapted in order to derive nonlinear Bell inequalities for a large class of causal networks and to identify quantumly realizable correlations that violate them.Artigo Semidefinite tests for quantum network topologies(Physical Review Letters, 2020-09-10) Åberg, Johan; Nery, Ranieri Vieira; Duarte, Cristhiano; Araújo, Rafael Chaves SoutoQuantum networks play a major role in long-distance communication, quantum cryptography, clock synchronization, and distributed quantum computing. Generally, these protocols involve many independent sources sharing entanglement among distant parties that, upon measuring their systems, generate correlations across the network. The question of which correlations a given quantum network can give rise to remains almost uncharted. Here we show that constraints on the observable covariances, previously derived for the classical case, also hold for quantum networks. The network topology yields tests that can be cast as semidefinite programs, thus allowing for the efficient characterization of the correlations in a wide class of quantum networks, as well as systematic derivations of device-independent and experimentally testable witnesses. We obtain such semidefinite tests for fixed measurement settings, as well as parties that independently choose among collections of measurement settings. The applicability of the method is demonstrated for various networks, and compared with previous approaches.Artigo Predicting topological invariants and unconventional superconducting pairing from density of states and machine learning(Physical Review B, 2025-01-02) Santos, Flávio Luis Noronha dos; Canabarro, Askery; Araújo, Rafael Chaves Souto; Pereira, Rodrigo G.Competition between magnetism and superconductivity can lead to unconventional and topological superconductivity. However, the experimental confirmation of the presence of Majorana edge states and unconventional pairing poses a major challenge. Here, we consider a two-dimensional lattice model for a superconductor with spin-orbit coupling and exchange coupling to randomly distributed magnetic impurities. Depending on parameters of the model, this system may display topologically trivial or nontrivial edge states. We map out the phase diagram by computing the Bott index, a topological invariant defined in real space. We then use machine learning (ML) algorithms to predict the Bott index from the local density of states (LDOS) at zero energy, obtaining high-accuracy results. We also train ML models to predict the amplitude of odd-frequency pairing in the anomalous Green's function at zero energy. Once the ML models are trained using the LDOS, which is experimentally accessible via scanning tunneling spectroscopy, our method could be applied to predict the number of Majorana edge states and estimate the magnitude of odd-frequency pairing in real materials.Artigo Quantum Finance: um tutorial de computação quântica aplicada ao mercado financeiro(Revista Brasileira de Ensino de Física, 2022-09-27) Silva, Askery Alexandre Canabarro Barbosa da; Mendonça, Taysa M.; Nery, Ranieri Vieira; Moreno, George; Albino, Anton S.; Jesus, Gleydson F. de; Araújo, Rafael Chaves SoutoAntes restrita a uma área de fronteira da Física, a computação quântica é uma das áreas que mais tem crescido atualmente, justamente por suas aplicações tecnológicas em problemas de otimização, aprendizagem de máquina, segurança da informação e simulações. O objetivo deste artigo é introduzir os fundamentos da computação quântica, tendo como foco um algoritmo quântico promissor e sua aplicação a um problema do mercado financeiro. Mais especificamente, discutimos o problema da otimização de portfólio usando o Quantum Approximate Optimization Algorithm (QAOA). Não somente descrevemos os principais conceitos envolvidos, mas também consideramos exemplos simples práticos, envolvendo ativos financeiros disponíveis na bolsa brasileira, com códigos, tanto clássicos quanto quânticos, dísponíveis livremente em um Jupyter Notebook. Também analisamos em detalhes a qualidade das soluções de otimização combinatória de portfólio por meio do QAOA usando o simulador quântico ATOS QLM do SENAI/CIMATEC.Artigo Criteria for nonclassicality in the prepare-and-measure scenario(Physical Review Research, 2020-10-20) Poderini, Davide; Brito, Samuraí Gomes de Aguiar; Nery, Ranieri Vieira; Sciarrino, Fabio; Araújo, Rafael Chaves SoutoQuantum communication networks involving the preparation, sharing, and measurement of quantum states are ubiquitous in quantum information. Of particular relevance within this context is to understand under which conditions a given quantum resource can give rise to correlations incompatible with a classical explanation. Here we consider the so-called prepare-and-measure scenario, in which a quantum or classical message with bounded dimension is transmitted between two parties. In this scenario we derive criteria witnessing whether a set of quantum states can lead or not to nonclassical correlations. Based on that, we show that quantum resources that can only give rise to classical correlations in the simplest prepare-and-measure scenario can have their nonclassicality witnessed if we increase the number of preparations or measurements.Artigo Enhancing entanglement and total correlation dynamics via local unitaries(Physical Review A, 2022-02-22) Varela, Joab Morais; Nery, Ranieri Vieira; Moreno Filho, Marcos George Magalhães; Viana, Alice Caroline de Oliveira; Landi, Gabriel; Araújo, Rafael Chaves SoutoThe interaction with the environment is one of the main obstacles to be circumvented in practical implementations of quantum information tasks. The use of local unitaries, while not changing the initial entanglement present in a given state, can enormously change its dynamics through a noisy channel, and consequently its ability to be used as a resource. In this way, local unitaries provide an easy and accessible way to enhance quantum correlations in a variety of different experimental platforms. Given an initial entangled state and a certain noisy channel, what are the local unitaries providing the most robust dynamics? In this paper we solve this question considering two-qubit states, together with paradigmatic and relevant noisy channels, showing its consequences for teleportation protocols and identifying cases where the most robust states are not necessarily the ones imprinting the least information about themselves into the environment. We also derive a general multipartite law relating the interplay between the total correlations in the system and environment with their mutual information built up over the noisy dynamics. Finally, we employ the IBM Quantum Experience to provide a proof-of-principle experimental implementation of our resultsArtigo Quantifying quantum causal influences(Physical Review A, 2023-08-28) Hutter, Lucas; Araújo, Rafael Chaves Souto; Nery, Ranieri Vieira; Moreno Filho, Marcos George Magalhães; Brod, Daniel JostCausal influences are at the core of any empirical science, the reason why its quantification is of paramount relevance for the mathematical theory of causality and applications. Quantum correlations, however, challenge our notion of cause and effect, implying that tools and concepts developed over the years having in mind a classical world have to be reevaluated in the presence of quantum effects. Here, we propose the quantum version of the most common causality quantifier, the average causal effect, measuring how much a target quantum system is changed by interventions on its presumed cause. Not only does it offer an innate manner to quantify causation in two-qubit gates but also in alternative quantum computation models such as the measurement-based version, suggesting that causality can be used as a proxy for optimizing quantum algorithms. Considering quantum teleportation, we show that any pure entangled state offers an advantage in terms of causal effects as compared to separable states. This broadness of different uses showcases that, just as in the classical case, the quantification of causal influence has foundational and applied consequences and can lead to a yet totally unexplored tool for quantum information science