Mestrado em Física (IF)

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Phenomenological study of neutrino invisible decay MINOS and MINOS+ experiments
(Universidade Federal de Goiás, 2025-04-03) Azevedo, Daniel Araújo de; Gomes, Ricardo Avelino; http://lattes.cnpq.br/6538341799051577; Gomes, Ricardo Avelino; Paulo Júnior, Ademar; Oliveira, Guilherme Colherinhas de
The neutrino oscillation model is already well stablished; however, there is still interest in investigating phenomena that may occur alongside it. One of them being decay, already ruled out as happening alone, but can still occur with oscillation. Some of the recent analysis in the literature try to, using experimental data from accelerator experiments, have a measurement of the parameter τ3/m3, carrying information about the decay of the mass eigenstate ν3. The following work consider the data from the MINOS and MINOS+ long-baseline experiments, for different models of neutrino oscillation: the standard oscillation and the oscillation with decay in vacuum and in matter. From the Pνµ→νµ probability, and considering the charged current events of νµ, we want to show: how the presence of the MINOS+ data affects the results obtained with the MINOS experiment; we also implement the oscillation with decay in matter model, which is a more suited one as a proof of concept, considering that modern studies do consider the matter effects; a value for the τ3/m3 parameter. This analysis also yields a best fit value for the oscillation with decay in matter of the combined experimental data, having ∆m 2 32 = 2.226 × 10−3 eV2 , sin2 θ23 = 0.715 and a lower bound limit of 90% C.L. for the decay parameter of τ3/m3 > 1.52×10−12 s/eV.
Gauge invariant quantum thermodynamics: foundations and applications to critical systems
(Universidade Federal de Goiás, 2025-04-04) Melo, Gabriel Fernandez Ferrari; Céleri, Lucas Chibebe; http://lattes.cnpq.br/6630683190018665; Céleri, Lucas Chibebe; Oliveira, Thiago Rodrigues de; Almeida, Norton Gomes de
In this formalism, thermodynamic quantities are described as functionals of the density operator and emerge from a coarse-graining process over all unitary transformations that preserve the system’s energy - a set we refer to as the thermodynamic group. This approach intrinsically incorporates informational access limitations to the system, constrained to energy basis measurements. Our contribution generalizes the expressions for invariant heat and work beyond the treatment presented in [3], explicitly including the consideration of dynamic degenerate energy levels. More than a formal extension, we establish a rigorous physical interpretation of these quantities through the non-unitary dynamics of the effective state obtained by the coarse-graining induced by the thermodynamic group. We demonstrate that the fundamental restriction to energy basis measurements implies the inaccessibility of part of the system’s energy, interpreted as an effective heat associated with the production of coherences in the energy basis. Consequently, the derived work corresponds to the system’s effective work, with its energetic contribution reduced by the portion allocated as heat. Within the second law context, we introduce the gauge-invariant entropy, proving it satisfies all required properties for a thermodynamic entropy. This entropy exhibits an explicit dependence on the thermodynamic group, manifested through an entropic contribution directly linked to the Hamiltonian’s spectral degeneracies. Crucially, we identify that the origin of entropy production coincides with that of heat in closed systems, both emerging from the inherent non-unitarity in the coarse-grained state’s dynamics. As a final application, we implement our formalism in the quantum dynamics of spin systems undergoing quenches, revealing that coherent heat captures signatures of irreversibility. In critical systems, the quantities derived within this theory prove fundamental for understanding modifications in the system’s symmetry structure relative to the internal symmetries of the thermodynamic gauge group
Líquidos iônicos de aminoácidos hidratados: uma alternativa para potencializar o armazenamento de energia em supercapacitores
(Universidade Federal de Goiás, 2025-02-21) Silva, Lucas de Sousa; Oliveira, Guilherme Colherinhas de; http://lattes.cnpq.br/0171051425848743; Oliveira, Guilherme Colherinhas de; Fileti, Eudes Eterno; Almeida , Agnaldo Rosa de
In this study, we employed Molecular Dynamics (MD) concepts to investigate the energy storage potential of supercapacitors (SCs) composed of amino acid ionic liquid (AAIL) electrolytes and graphene electrodes. The choice of amino acid derivatives was motivated by their biodegradability, aligning with increasing environmental concerns. Our investigation focused on systems containing the cation 1-ethyl-3-methylimidazolium (Emim) and the amino acids alanine (Ala), valine (Val), leucine (Leu), and isoleucine (Ile), considering different electrolyte hydration levels ranging from 10% to 40%, as well as a low ionic concentration condition with 90% water content. The results indicated that the devices achieved maximum energy storage capacity under 90% hydration. We conclude that the use of AAILs as electrolytes in supercapacitors holds excellent potential for energy storage devices, demonstrating superior performance compared to systems with conventional electrolytes and similar electrodes, while also standing out for their biodegradability and cost-effectiveness.
Identificação de estrelas do tipo A na base de dados do S-PLUS e estimativas de seus parâmetros atmosféricos
(Universidade Federal de Goiás, 2025-03-12) Sampaio, Franklin Tyerry Silva; Santucci, Rafael Miloni; http://lattes.cnpq.br/7644987837821138; Santucci, Rafael Miloni; Placco, Vinicius Moris; Perottoni, Hélio Dotto
This work aims to identify candidate A-type stars within the Southern Photometric Local Universe Survey (S-PLUS) database. The data from this purely photometric survey were cross-matched with other databases to gather reference spectroscopic and astrometric information. Through comparisons, limits were defined for the selection of A-type stars using S-PLUS photometry. With the aid of a robust statistical tool, the Gaussian Mixture Model (GMM), criteria were established to distinguish between blue horizontal branch (BHB) stars and main sequence stars in a sample of A-type stars from S-PLUS. The main atmospheric parameters, like Teff , log g and [Fe/H], were determined for thousands of A-type stars using a symbolic regression software. Finally, the distance were estimated through an absolute magnitude calibration for the selected BHB stars.
Um estudo sobre termodinâmica e informação em modelos holográficos
(Universidade Federal de Goiás, 2024-12-20) Costa, Ronaldo Ferreira; Céleri, Lucas Chibebe; http://lattes.cnpq.br/6630683190018665; Pereira, Rômulo Cesar Rougemont; http://lattes.cnpq.br/9207462207391635; Pereira, Romulo Cesar Rougemont; Acevedo, Willians Oswaldo Barreto; Guimarães, Marcelo Santos
This dissertation addresses aspects of information theory and thermodynamics in the context of gauge/gravity duality, focusing on two specific holographic models: 1RCBH and 2RCBH. The study analyzes fundamental concepts of information theory, such as entanglement entropy and discusses gauge/gravity duality as a tool for analyzing thermodynamic and information properties of these models. Initially, we review in detail the thermodynamics of the 1RCBH model, which is a toy-model for a strongly-coupled quantum field theory at finite temperature and density and has a critical point in its phase diagram, while the 2RCBH model describes a different strongly-coupled quantum field theory, also defined at finite temperature and density, but without a critical point in its phase diagram. The main focus of the research is to calculate thermodynamic and information observables using holographic gauge/gravity duality in these models. We also review the entanglement entropy of the 1RCBH model, and, as an original contribution, we propose a new and more efficient method to evaluate it than previously considered in the literature. Due to some numerical issues still to be understood and solved, a detailed analysis of the entanglement entropy in the 1RCBH and 2RCBH models will be postponed to an upcoming work intended for publication.
Quebra de simetria em condensados de Bose-Einstein confinados por um potencial funil
(Universidade Federal de Goiás, 2021-04-09) Miranda, Bruno Martins; Cardoso, Wesley Bueno; http://lattes.cnpq.br/6845416823133684; Cardoso, Wesley Bueno; Malbouisson, Jorge Mário Carvalho; Almeida, Norton Gomes de
Theoretically predicted in 1923-1924 by Bose and Einstein and experimentally obtained only in 1995, the Bose-Einstein condensate became an important laboratory for the investigation of various quantum phenomena, such as the Josepshon oscillations, the study of vortex, use as interferometers, etc. Using mean-field theory to include the effects of the average interaction between particles, in the 1960s, Gross and Pitaevskii obtained an equation capable of describing the dynamics of a diluted gas at a temperature of 0 K. Dimensional reduction models for the Gross-Pitaevskii equation were developed for several types of confining potentials in order to simplify numerical calculations and reproduce accurate results. For condensates with a strong attractive strength, confined by doublewell potentials, it is known that the phenomenon of spontaneous symmetry breaking occurs. In this state, the particle population between wells becomes asymmetrical, in contrast with the symmetry of the confining potential. In this work, we consider a condensate in the self-focusing regime, confined transversely by a funnel-like potential and axially by a double well formed by the combination of two inverted Pöschl-Teller potentials. We used an effective equation, obtained by means of a variational method for the Gross-Pitaevskii equation, to analyze the symmetry break of the probability density of the wave function that describes the condensate. This symmetry break was observed for several interaction strength values as a function of the minimum potential well. A quantum phase diagram was obtained, in which it is possible to recognize the three phases of the system: symmetric phase (Josepshon), asymmetric phase (spontaneous symmetry breaking - SSB), and collapsed states, i.e., when the solution becomes singular, which does not represent the physical system, showing a validity limit for the model under consideration. We analyzed our symmetric and asymmetric solutions using the real-time evolution method, in which it was possible to confirm the stability of the results. Finally, a comparison with the cubic nonlinear Schrödinger equation in one dimension and the Gross-Pitaevskii equation in three dimensions is performed for the purpose of analyzing the accuracy of the effective equation used here.
The dynamical Casimir effect and the generation of thermodynamic entropy
(Universidade Federal de Goiás, 2024-03-12) Oliveira, Gustavo de; Céler, Lucas Chibebe; http://lattes.cnpq.br/6630683190018665; Céler, Lucas Chibebe; Landi, Gabriel Teixeira; Maia Neto, Paulo Américo
In this dissertation, we investigate the dynamics of the thermodynamic entropy production in the dynamical Casimir effect. This is done by considering a quantum scalar field confined by a one-dimensional cavity composed of a pair of ideal mirrors, one fixed and the other allowed to move in a prescribed trajectory. The central goal of this work is to understand how the thermodynamic entropy of the field evolves over time due to the particle creation process induced by the non trivial boundary conditions imposed by the moving mirror. By employing an effective Hamiltonian approach, the system’s entropy production is shown to increase with the number of particles created within the short-time limit. Moreover, one can also demonstrate that this approach is directly related to the generation of quantum coherence in the energy basis of the field. Utilizing a distinct method, grounded in the theory of Gaussian states, we were able to analyze the long-time limit of the entropy production for a single mode of the field. The obtained results establish a relationship between the increase in thermodynamic entropy in the field mode and the entanglement between the considered mode and the rest of the field mode structure. In this way, we link the entropy production in the field due to the dynamical Casimir effect with two fundamental features of quantum mechanics: quantum coherence and entanglement.
Entropy production in quantum systems and Nernst heat theorem for a single qubit
(Universidade Federal de Goiás, 2024-02-23) Sousa, Aryadine Fernandes de; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Almeida, Norton Gomes de; Souza, Alexandre Martins de; Moraes Neto, Gentil Dias de
Classical thermodynamics, which focuses on macroscopic systems in equilibrium, has given rise to various theories to address systems out of equilibrium over time. Recently, quantum thermodynamics has emerged as a theory dedicated to describe microscopic quantum systems. A notable application of this theory is found in the development of thermal engines, where the working substance is a microscopic quantum system. In this work, we present the essential theoretical formulation to understand entropy production in quantum systems and its impact on thermal machines. The approach involves exploring quantum friction and conducting a deeper analysis of the laws of thermodynamics on a fundamental scale. Examining the effects of these phenomena in a Quantum Otto Heat Engine, we highlight the implications of quantum friction on engine performance. Particularly noteworthy is the observation that operating the cycle with a reservoir with effective negative temperature enhances the engine efficiency significantly. This improvement is attributed to strategic choices in the populations of excited states in the reservoirs, revealing an innovative approach to optimizing performance in quantum systems. Additionally, we extend the Nernst heat theorem for a single qubit. This result not only presents intriguing theoretical implications but is also supported by numerical simulations and experiments using Nuclear Magnetic Resonance (NMR). These pieces of evidence uphold the remarkable convergence of Helmholtz free energy and internal energy as the temperature approaches zero Kelvin, underscoring the practical applicability of these theorems in quantum systems.
Estudos de materiais dopados com íons lantanídeos para aplicações em nanotermometria
(Universidade Federal de Goiás, 2023-10-31) Silva, Daniel Lopo da; Maia, Lauro June Queiroz; http://lattes.cnpq.br/9454054374479016; Maia, Lauro June Queiroz; Poirier, Gaël Yves; Santana, Ricardo Costa de
Optical phenomena such as luminescence of materials depend on several characteristics such as temperature, dopants, crystalline structure, etc. Electromagnetic emissions from materials doped with rare-earth ions can provide thermal information regarding the environment where these materials are inserted. Materials with good thermal sensitivity are considered promising for the development of technologies for nanoscale temperature measurements. In this work, nine samples previously prepared through different synthesis routes such as sol-gel process and modified Pechini were analyzed. The samples studied have matrices of several compounds such as aluminum borates (Al4B2O9) monophasic and embedded in silica, aluminum germanates (Al6Ge2O13) monophasic and embedded in silica, yttrium borates (YBO3) and yttrium aluminum silicates (YAS). Altogether, five trivalent lanthanide ions were used as dopants of the samples: Nd, Eu, Er, Tb and Yb. The emission spectra of the samples were analyzed at seven different temperatures from 25 °C to 55 °C with a variation of 5 °C. Diffuse reflectance spectra were studied to confirm the presence of ions in the matrix and enable the calculation of the energy gap for each sample. From the emission spectrum, photoluminescent intensity ratios (RIFs) were calculated for the calculation of relative thermal sensitivities. The sample that showed the highest value for relative thermal sensitivity (Sr) was the one with the composition YBO3 : Nd3+, Eu3+, Er3+, Yb3+, Tb3+ synthesized at 900°C, presenting a value of Sr = (1,52 ± 0,20) %.K-1 in the temperature range of 35°C and 55°C.
Estudo das interações dos surfactantes iônicos SDS, CTAC e HPS e miltefosina com membranas de leishmania, macrófagos e eritrócitos
(Universidade Federal de Goiás, 2023-09-18) Cardoso, Éder Jéferson Souza; Alonso, Antônio; http://lattes.cnpq.br/5013069863616789; Alonso, Antônio; Mendanha Neto, Sebastião Antônio; Silva, Kleber Santiago Freitas e
Miltefosine (MT) is an internationally approved oral drug for the treatment of leishmaniasis, however, its mechanism of action is not yet well established. Understanding the mechanism of action of compounds with leishmanicidal activity is important to help in the search for new drug prototypes with greater activity and fewer side effects. Surfactants are compounds widely used in the industry in the manufacture of soap, shampoos and other cosmetics. They are usually classified according to the molecular charge, and may be nonionic, anionic, cationic or zwitterionic (or amphoteric) when they have a positive and negative charge in the same compound. Electron Paramagnetic Resonance (RPE) spectroscopy associated with the spin-label method was used to compare the interactions of MT and the surfactants Sodium Dodecyl Sulfate (SDS, anionic), Cetyl Trimethyl Ammonium Chloride (CTAC, cationic) and N, N-dimethyl-3-ammonio-1-propanesulfonate (HPS, zwitterionic) with the membranes of Leishmania (L.) amazonensis, erythrocyte and macrophage. All compounds increased the molecular dynamics of membrane proteins; however, SDS caused the smallest increase in parasite and erythrocyte membrane dynamics and was also the least effective in antileishmanial activity, cytotoxicity in macrophages J774.A1 and hemolytic potential in both PBS and whole blood. It was detected, in blood plasma, the albumin stiffness caused by 2.5 mM SDS due to the electrostatic and hydrophobic interactions of the compound with the protein. CTAC did not show significant differences in relation to the other compounds, but at higher cell concentrations (>1x109 cells/mL), it showed high activity against the L. amazonensis promastigotes, besides being the most cytotoxic to macrophages J774.A1. For all the experiments, the zwitterionic molecules HPS and MT did not present significant differences between them. The data suggest the possibility of using cationic or zwitterionic surfactants in formulations containing leishmanicides, aiming at the treatment of cutaneous leishmaniasis.
Landauer principle in the context of relativistic communication theory
(Universidade Federal de Goiás, 2023-04-25) Alvim, Yuri de Jesus; Céleri, Lucas Chibebe; http://lattes.cnpq.br/6630683190018665; Céleri, Lucas Chibebe; Vanzela, Daniel Augusto Turolla; Pereira, Rômulo Cesar Rougemont
This monograph aims to investigate Landauer's principle for a quantum system in a relativistic context. Specifically, we consider a communication channel described by a mode of a quantum field in a curved spacetime. In order to accomplish that, an introduction to Shannon's theorems, as well as some very important concepts in information theory, will be first presented. The relativistic spacetime structure will be described in the sequence, such that the quantum field theory can be used, in this context, to describe the communication channel. Lastly, the calculation of the channel capacity and the energy contributions for the transmission of information over such a channel will be done. Such calculations provide three different contributions to the total energy variation of the system: one due to the change in the spacetime, one associated with the work necessary to switch on or off the interaction between the detectors ---qubits employed to read and codify the information--- with the field and, finally, the last one which is due to the communication process itself. This third contribution vanishes for the considered communication channel, so that no extra energy cost is needed to transmit information once the states of the qubits are settled. The original contribution of this work enters here by considering the cyclical conversion of the transmitted information into work. Since no energy is transferred from the sender to the receiver, this engine apparently violates the second law of thermodynamics. By employing Landauer principle we find the energy contribution which allows the receiver to convert information into work without contradictions with thermodynamics.
Quantum thermodynamics: a modified otto engine
(Universidade Federal de Goiás, 2023-03-02) Matos, Richard Quintiliano; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Almeida, Norton Gomes de; Moraes Neto, Gentil Dias de; Gomes, Rafael de Morais
Quantum thermodynamics is an emerging area that arouses the interest of many scientists and engineers. Although it is a new and incomplete theory, it comes with surprising results. We propose to study a quantum engine that utilizes thermal reservoirs as baths but an unusual system as working fluid, a squeezed harmonic oscillator. The fluid was chosen as an educated guess to study if an engine working solely with a quantum resource could surpass Carnot’s limit. The problem was solved analytically and then simulated using the qutip library to python, we showed that this engine is capable of working in Carnot’s regime. Furthermore, we calculated the Shortcut to adiabaticity to the evolving hamiltonian so we could improve the system’s power without losing efficiency. This kind of machine serves the purpose of showing that one cannot surpass Carnot’s limit if one is using thermal reservoirs.
Modelagem teórica para melhoramento da eficiência energética em supercapacitores
(Universidade Federal de Goiás, 2023-03-01) Chagas, Henrique de Araujo; Oliveira, Guilherme Colherinhas de; http://lattes.cnpq.br/0171051425848743; Oliveira, Guilherme Colherinhas de; Castro, Marcos Antonio de; Andrade, Douglas Xavier de
Two-dimensional carbon materials, such as graphene and graphyne, have stood out in energy storage applications due to their unique physical, chemical, and electronic properties. Graphyne, in particular, presents even more remarkable properties, such as higher specific area, electronic mobility, and intrinsic energy band. Furthermore, biocompatible ionic liquids (ILs), such as those formed by choline and glycine, are increasingly being studied as a less toxic alternative for the environment. This work performed molecular dynamics simulations to investigate the properties of electrolytes based on aqueous mixtures of the biodegradable IL [Ch][Gly] with the IL [Bmim][PF6] as electrolytes in graphyne supercapacitors. Through energetic, structural, and electrostatic analyses, it was possible to describe the Electric Double Layer (EDL) formed near the electrodes. It was found that, although the structure and formation of the EDL are governed by a complex network of electrostatic and van der Waals (vdW) interactions, their interaction with the electrode is dominated by vdW interactions. It was observed that choline-based electrolytes can perform as well as most conventional ILs, but with the advantage of low toxicity. The comparison between graphyne and graphene supercapacitors for the IL mixture revealed a higher capacitance for graphyne, even when comparing similar values for the potential drop. Subsequently, an extensive comparison of electrode performances in energy storage applications under thermodynamic conditions was performed. The electrostatic properties of eight different supercapacitors, four made of graphene and four made of graphyne, in different electrolytes were investigated. A detailed analysis of the energy and organization of the electric charges of these systems is reported for all systems. The results indicate the superiority of the graphyne electrode over the graphene electrodes, confirming previous findings and making graphyne a promising candidate for electrochemical energy storage systems. Thus, this study contributes to the understanding of the properties of two-dimensional carbon materials and their application in energy storage devices.
Modelagem de membranas peptídicas formadas por arginina e fenilalanina usando dinâmica molecular
(Universidade Federal de Goiás, 2023-03-08) Soares, Karinna Mendanha; Oliveira, Guilherme Colherinhas de; http://lattes.cnpq.br/0171051425848743; Oliveira, Guilherme Colherinhas De; Almeida, Agnaldo Rosa de; Cardoso, Wesley Bueno
The use of computational resources for modeling organic nanostructures from peptides has a potential to elucidate fundamental characteristics that guide molecular interactions and that collaborate with the understanding of the selfassembly process of these materials. In this study, we describe a structural and energetic study of a membrane using molecular dynamics. Our simulations were carried out by exploring three ways of juxtaposition between the peptides that shape the organic nanostructure. The simulations also shows that the three forms of organization are viable during the self-assembly process leading to similar structures. Our studies reinforce the importance of hydrogen bond and the correct modeling of the hydrophobic and hydrophilic structure of the peptide in the nanomembrane idealization process (especially bola-amphiphilic peptide). For membrane thickness, our results obtained from the mass density profile were 2,28; 2,25 and 2,22 nm. From the surface mapping we found the results 2,47; 2,14 and 2,32 nm, that differs by up to 2,36 nm from the experimental result of 3,2 – 4,5 nm. This led us to adopt a bilayer model in which the results highlight an average thickness of 3,95 nm indicating that the experimental results may be indicate the presence of structures bilayers model and not monolayers.
Propriedades ópticas não lineares de um novo derivado de quinolinona
(Universidade Federal de Goiás, 2022-09-23) Vinhal, Rafael de Siqueira; Osório, Francisco Aparecido Pinto; http://lattes.cnpq.br/1354763162575957; Osório, Francisco Aparecido Pinto; Torres, Elber Magalhães; Fonseca, Tertius Lima da
In this work we have studied the linear and nonlinear optical properties of a quinolinone derivative4(1H)-quinolinone-(E)-4-bromobenzylidene-4-chlorophenyl-phenylsulfonyl (QBCP) with formula C28H19BrClNO3S. The theoretical calculations of the electrical properties of the QBCP crystal were performed at the Density Functional Theory (DFT) level with the CAM-B3LYP functional and the 6-311++G (d,p) basis function, both in the static and dynamic regime. To better understand the optical properties of the QBCP molecule, we obtained the HOMO-LUMO boundary orbitals and through their energies we calculated the global reactivity parameters such as the gap energy, the ionization energy, the electronic affinity, the global hardness, among others. We also calculated using the TD-DFT theory the absorption and emission spectrum in the ultraviolet (UV-Vis) of QBCP, making it possible to calculate the Stokes shift, we also studied the absorption spectrum in the infrared (IR) of the QBCP molecule. And the intermolecular interactions of QBCP were studied through the Hirshfeld Surface analysis. The results obtained for the optical properties of the QBCP molecule were very good when compared with the results obtained for other organic crystals, suggesting that it can be studied as a possible nonlinear optical material.
Quantum refrigerators operating under effective negative temperatures
(Universidade Federal de Goiás, 2023-02-24) Damas, Gabriella Gonçalves; Assis, Rogério Jorge de; http://lattes.cnpq.br/7703787869253387; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Almeida, Norton Gomes De; Souza, Alexandre Martins de; Maia, Leonardo Paulo
Ao longo das últimas décadas, uma nova teoria tem sido desenvolvida com o intuito de descrever a termodinâmica de sistemas quânticos microscópicos, a qual ficou conhecida como termodinâmica quântica. Uma aplicação interessante dessa teoria está no desenvolvimento de motores térmicos nos quais a substância de trabalho é um sistema quântico microscópico, esses dispositivos passaram a ser conhecidos como motores térmicos quânticos. Dentro desse contexto, o estudo de refrigeradores quânticos tem atraído bastante atenção especialmente para sua aplicação potencial em sistemas nanoscópicos. Nesse contexto, a presente dissertação apresenta dois estudos relacionados a um refrigerador quântico autônomo. No primeiro estudo, abordamos um refrigerador autônomo composto por três qubits operando com um dos reservatórios com temperaturas negativas, que tem como finalidade resfriar um dos qubits. Encontramos os valores da temperatura mais baixa possível que o qubit de interesse atinge ao fixar os parâmetros relevantes e também analisamos o limite para resfriar o qubit arbitrariamente próximo ao zero absoluto. Procedemos assim a um estudo comparativo mostrando que reservatórios com temperaturas negativas efetivas são mais poderosos do que aqueles em temperaturas positivas para resfriar o qubit de interesse. No segundo estudo, realizamos um estudo de caso de um refrigerador quântico operando na presença de reservatórios térmicos bosônicos ou fermiônicos, e mostramos que os banhos fermiônicos apresentam vantagens sobre os bosônicos. Por fim, é feita uma discussão sobre o uso de reservatórios com população invertida e a medida de eficiência utilizada para esses sistemas.
Propriedades estatísticas de fótons de micro-ondas gerados por uma junção túnel
(Universidade Federal de Goiás, 2022-10-30) Campos, Maikon Bruno Alves; Mendes, Udson Cabral; https://lattes.cnpq.br/2549501479254454; Mendes, Udson Cabral; Almeida, Norton Gomes de; Silva, Cláudio José da
In this dissertation, we investigate the statistical properties of microwave photons generated by a tunnel junction coupled to a microwave resonator. For that, we developed the master equation formalism to calculate the statistical properties of (i) an electromagnetic field mode coupled to a thermal reservoir and (ii) to a squeezed vacuum reservoir. Furthermore, we derived the Hamiltonian of the tunnel junction coupled to a microwave resonator. This allows us to derive the master equation for the tunnel junction coupled to a microwave resonator and Confirm that (i) in the absence of ac voltage, the junction behaves as a thermal reservoir and (ii) in the presence of an ac voltage oscillating at a frequency equal to twice the frequency of the resonator, the junction behaves as a squeezed reservoir. Also we studied the tunnel junction coupled to a microwave resonator subjected to ac voltage with a frequency equal to three times the resonator frequency, theoretically demonstrating the possibility of generating photon trios, which has already been explored experimentally, but which has yet to be has no theoretical explanation for these experiments.
Structural and electronic properties of functionalized germanene
(Universidade Federal de Goiás, 2020-06-09) Oliveira, Flávio Bento de; Rosa, Andreia Luísa da; http://lattes.cnpq.br/1038061895538870; Rosa, Andreia Luísa da; Lima, Erika Nascimento; Bufaiçal, Leandro Felix de Sousa
The study of two-dimensional (2D) materials has increasing interest after the discovery of graphene whose property differed surprisingly from its three-dimensional form. 2D materials have electrical properties of great interest for technological applications, and play a role in the reduction of the dimensions of the electronic devices that are currently produced as well. Graphene in its honeycomb structure has a zero gap, with conducing and valence bands being degenerate at K and K’ points, forming cones. However, difficulties in carrying out and adjusting a reasonable sizeable band gap in graphene is attracting increasing interest to other two-dimensional materials. One of the promising material is a single layer of germanium, the so-called germanene. Recent investigations suggest that germanium layers react rapidly with the environment. This may affect not only their electronic structure, but also their reactivity and optical properties. Therefore one may search for ways of tuning the electronic properties of these twodimensional layers. A promising route for tuning the electronic structure of bare layered materials is the adsorption of organic molecules or functional groups. Recently, germanene has been synthesized to create hybrid layers upon adsorption of organic ligands. In this work, band gap tuning of organic ligands adsorbed on bidimensional germanium monolayers have been investigated using first-principles calculations. We show that the adsorption of these small groups retains the initially stable free-standing pristine buckled germanium nanostructures. We claim that the stability of these structures stem from both strain induced by the adsorption of this organic group and ligand-ligand interactions. Our studies of a finite band gap form the way for a rational design of germanium nanostructures, which can find applications in electronic devices.
Redução dimensional para condensados de Bose-Einstein em forma de “tubo” e “anilha plana”
(Universidade Federal de Goiás, 2019-02-28) Santos, Mateus Calixto Pereira dos; Cardoso, Wesley Bueno; http://lattes.cnpq.br/6845416823133684; Cardoso, Wesley Bueno; Avelar, Ardiley Torres; Santana, Ademir Eugênio de
The study of nonlinear dynamics represents a challenge of contemporary physics. In particular, the investigation of Bose Einstein condensates proved to be a hard task due to the large number of interacting particles. Therefore, given the difficulty of modeling these systems, approximations were introduced, which promoted the description of the Bose-Einstein condensation state in interacting atomic gases as a three-dimensional nonlinear Schrödinger equation, known as the Gross-Pitaevskii equation. In this work we review the dimensional reduction method, which use a variational treatment with the goal of derive effective one-dimensional (1D) and two-dimensional (2D) equations in cigar-shaped and pancake-shaped Bose-Einstein condensates, where we show that these equations describe almost exactly the dynamics of their respective models. Thus, we studied the ground-state solutions in tube-shaped and flat washer-shaped Bose-Einstein condensates by means of effectives non-polynomials equations, derived from the dimensional reduction method. The results produced by this equations were in very good agreement with those obtained from the corresponding full 3D Gross-Pitaevskii equation.
Relativistic symmetry in quantum information theory
(Universidade Federal de Goiás, 2022-04-04) Bidinotto, Alexandre Borges; Taillebois, Emile Raymond Ferreira; Avelar, Ardiley Torres; http://lattes.cnpq.br/5732286631137637; Avelar, Ardiley Torres; Santana, Ademir Eugênio de; Cardoso, Wesley Bueno
This dissertation begins with a succinct introduction to group theory to enable the understanding of special relativity theory from a symmetrical point of view. From this perspective, the notion of hierarchy of dynamical variables, which is present in relativity, is introduced to quantum mechanical formalism in order to construct the irreducible unitary representations of the Poincaré group for secondary variables. Given this discussion, the questions regarding the existence of a subset of transformations in which the Wigner rotations associated do not depend on the momenta. In sequence, the relativistic Stern-Gerlach observable is presented. This observable also depends on the momenta, so the initial problem on the density matrices for spin remains unsolved. The open question on the Stern-Gerlach observable is what is the minimum number of measurements in order to fully determine a relativistic density matrix. Both questionings on this dissertation can lead to the determination of the quantum state tomography of relativistic particles, which is the further goal of this document.

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