Eficiência de um motor térmico de Otto quântico baseado em um sistema de dois níveis
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2021-12-09
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Universidade Federal de Goiás
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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.
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ASSIS, R. J. de. Eficiência de um motor térmico de Otto quântico baseado em um sistema de dois níveis. 2022. 86 f. Tese (Doutorado em Física) - Universidade Federal de Goiás, Goiânia, 2021.