Programa de Pós-graduação em Física

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http://200.137.215.59/tede/handle/tde/276

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Agora exibindo 1 - 9 de 9

Dinâmica populacional em sistemas atômicos de dois e três níveis de energia
(Universidade Federal de Goiás, 2017-08-10) Alves, Eyber Domingos; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Oliveira, Guilherme Colherinhas de; Almeida, Agnaldo Rosa de
In this work a description of the interaction between electromagnetic radiation and matter will be made. Two and three-level atomic systems will be addressed, which in turn is in the (Lambda) configuration.We will use the Dicke states to calculate the transition probability between the energetic levels for a 2-level ensemble of atoms interacting with a circularly polarized field. We will deduce the master equation for a two-level atom interacting with a thermal reservoir, observing the effects of irreversible spontaneous decay and loss of coherence between quantum states. Finally, we will study the phenomenon of Electromagnetically Induced Transparency (EIT) and Dark states.
Tratamento de sistemas abertos via reservatórios térmicos bosônico e fermiônico
(Universidade Federal de Goiás, 2019-04-15) Araújo, Dannilo Iágor Evangelista de; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Almeida, Norton Gomes de; Colherinhas, Guilherme; Almeida, Agnaldo Rosa de; Cardoso, Wesley Bueno; Sales, José de Sousa
We developed this work at the moment with the objective to resolver the master equation for both thermal reservoir: bosonic and fermionic, as well as the master equation in reservoirs of vacuum and of Fock compressed . the bosonic thermal reservoir is modeled by a collection of coupled harmonic oscillators and the fermionic reservoir by a collection of two-level atoms. We made use of the Jaynes-Cummings model and the Bohr, Bohr-Markov and Markov approaches. In the end we discussed the application to the master equation for two distinct phenomena, Cooling by Heating (CBH) analyzing average energy graphs to the atomic system versus number of photons, and the average energy of the bosonic system as a function of the mean number of phonons, we observed the negative temperature in the absolute scale due to the inversion of population of states in function of cooperativity, we also analyzed a signature of negative response in a three level system interacting in a optical cavity, that comes as a result of decrease in the output field intensity when the input field intensity is increased.
POVM no contexto de eletrodinâmica quântica de cavidades
(Universidade Federal de Goiás, 2017-03-13) Assis, Rogério Jorge de; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Almeida, Norton Gomes de; Villas-Boas, Celso Jorge; Almeida, Agnaldo Rosa de
In this work it is proposed a simplified scheme to unambiguously discriminate between one of two nonorthogonal cavity field states. This scheme, which is based on POVM - positive operator valued measure, uses one three-level atom as the ancilla to obtain information on the cavity field state, the target. The efficiency of this scheme in discriminating the two quantum states is analy zed by comparing the maximum theoretical success probability with the maximum success probability possible to our case.
Eficiência de um motor térmico de Otto quântico baseado em um sistema de dois níveis
(Universidade Federal de Goiás, 2021-12-09) Assis, Rogério Jorge de; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Almeida, Norton Gomes de; Serra, Roberto Menezes; Cardoso, Wesley Bueno; Brito, Frederico Borges de; Pinto, Diogo de Oliveira Soares
Classical thermodynamics, also called equilibrium thermodynamics, is a theory that deals with macroscopic systems in equilibrium. After its development, other theories emerged to encompass macroscopic out-of-equilibrium systems. Over the past few decades, researchers have developed a new theory to describe also the thermodynamics of microscopic quantum systems, which became known as quantum thermodynamics. An important application of this theory is in the development of heat engines in which the working substance (the substance responsible for transforming heat into work) is a microscopic quantum system. Due to their composition, these devices came to be commonly called quantum heat engines. Notably, recent studies have shown that using an out-of-equilibrium reservoir as a heat source can improve the performance of quantum heat engines, compared to the usual case where the heat source is an equilibrium reservoir (a thermal reservoir). In this context, this thesis presents two studies related to a quantum Otto heat engine whose working substance is a two-level system: in the first study, the engine has a squeezed thermal reservoir as the heat source, while in the second study, the heat source is a reservoir with a negative temperature. Both studies explore the finite-time regime of the expansion and compression stages of the heat engine. The first study shows that the engine efficiency can be greater than the Carnot efficiency in both the quasi-static and finite-time regimes. However, as in the usual case, decreasing the time of the expansion and compression stages degrades the engine efficiency. In its turn, the second study shows that the engine efficiency can surpass the Otto efficiency in the finite-time regime. Here, different from the usual case, decreasing the time of the expansion and compression stages can increase the engine's efficiency. Finally, the present thesis shows an experimental scheme in the nuclear magnetic resonance context able to provide a proof of concept for the engine in the different situations studied.
A possible inadequacy of a recent proposal for redefining heat and work in quantum thermodynamics
(Universidade Federal de Goiás, 2021-03-15) Bottosso, Eduardo Borges; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Moussa, Miled Hassan Youssef; Céleri, Lucas Chibebe; Almeida, Norton Gomes de
A primeira identificação de um sistema quântico aberto como um modelo para um motor térmico quântico data de 1959. Desde então, a física não tem um conjunto concreto de fórmulas para definir, com precisão, como lidar com o calor e trabalhar no contexto de conjuntos quânticos . Uma das propostas mais proeminentes, que foi afirmada pelo artigo de R. Alicki de 1979, tem um regime de validade limitado e pode levar a algumas inconsistências com relação à primeira lei da termodinâmica. Várias abordagens para o problema foram propostas, levando a um novo conjunto de definições para calor e trabalho em termodinâmica quântica. Particularmente, novas redefinições para calor e trabalho foram introduzidas, as quais são baseadas na entropia de von Neumann. Nosso objetivo aqui é apresentar essa nova formulação, bem como sua motivação e investigar as consequências dessas fórmulas. Estudamos alguns modelos simples que empregam esse novo conjunto de definições. Nossa análise mostra um comportamento peculiar dos sistemas quânticos quando esse novo formalismo é dado como certo, possivelmente indicando uma inadequação dessas novas definições.
Estudo termodinâmico de sistemas quânticos caóticos via Teoria de Matrizes Aleatórias
(Universidade Federal de Goiás, 2016-08-22) Cavalcante, Eric Gomes Arrais; Céleri, Lucas Chibebe; http://lattes.cnpq.br/6630683190018665; Almeida, Norton Gomes de; http://lattes.cnpq.br/3182841849332242; Almeida, Norton Gomes de; Céleri, Lucas Chibebe; Avelar, Ardiley Torres; Villas-Bôas, Celso Jorge
Results from classical Random Matrix Theory (RMT) are well recognized as a way to describe spectral statistical properties of classically chaotic quantum systems, such as the level spacing distribution. We investigate, both numerically and analytically, if RMT can be used, at least for some regimes, to predict the behavior of the statistics of work performed by quenching some external parameter dictating the dynamics of a quantum chaotic system. This is done by comparison of the characteristic function of work obtained numerically from a well known quantum chaotic system called Dicke Model and from matrices pertaining to one of the classical ensembles of RMT, namely GOE. We also show one analytical result for the RMT average of the characteristic function that holds in the limit of high temperatures.
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.
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.
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.

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