http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/4372 Tue, 23 Sep 2025 21:44:53 GMT 2025-09-23T21:44:53Z http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/9773 Título: Fonte de pares de fótons quanticamente correlacionados gerados por conversão paramétrica descendente espontânea com cristal PPKTP bombeado por um laser de diodo de baixo custo Autor: OLIVEIRA, Nallyson William Santos Primeiro orientador: NUNES FILHO, José Ferraz de Moura Abstract: The rapid growth of the quantum technologies industry has propelled intelligent solutions for cost reduction in scientific research. A commonly employed strategy involves the use of diode lasers for the pumping process in sources based on spontaneous parametric downconversion. This is justified by the fact that, when compared to conventional lasers, diode lasers demonstrate significant cost-effectiveness advantages. In this context, a homemade control system was utilized for the diode laser, aiming to present an economically viable alternative. In this dissertation, we undertook the construction of the current controller for a diode laser and its characterization. The objective is to use this laser in the generation of photon pairs with quantum correlations through the process of spontaneous parametric down-conversion, occurring in nonlinear crystals. In this dissertation, we employed a PPKTP crystal with type II phase matching, where the pairs are generated collinearly to the pump beam. Using the Cauchy-Schwarz inequality, expressed in terms of the parameter R, where for R > 1 non-classical effects are observed, we measured the violations of this inequality during the conducted experiments. We obtained a maximum value of R = 65 ±22, highlighting the violation of the inequality and validating the successful construction of the correlated photon source using a diode laser for pumping. Instituição: Universidade Federal Rural de Pernambuco Tipo do documento: Dissertação Fri, 08 Mar 2024 00:00:00 GMT http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/9773 2024-03-08T00:00:00Z http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/9379 Título: Transferência de mágnons em cadeias de Heisenberg desordenadas Autor: LIMA, Wilma Valeria Pereira de Primeiro orientador: LIMA, Jonas Romero Fonseca de Abstract: This work investigates the magnon transference throughout a disordered Heisenberg chain. We considered a model consisting of a source S, site number one, connected to a receiver R, in the last site, using Heisenberg spins. The inner sites work as a channel connecting S and R. In our model, the Heisenberg coupling between nearest-neighbor spins at the channel are random numbers. In addition, we also include an external magnetic field. In our model, the magnetic field is also random numbers uniformly distributed. The coupling between the sites S and R and the inner sites is a tunable parameter called g. Our calculations were done by considering a spin deviation at site number one and obtaining its propagation for long times. Our analyzes indicate that for g much smaller than one e for a weak disorder, it is possible to obtain quantum transfer of magnon from the first to the last site whenever the effective diagonal energies of the first and from the last site are close to the uniform mode, E = 0. We discuss in detail the necessary conditions to maintain this magnon transfer. In particular, we obtained approximately mean maximum values for disorder in internal couplings and field disturbance magnetic, which we can choose to keep good transfer. Instituição: Universidade Federal Rural de Pernambuco Tipo do documento: Dissertação Wed, 01 Mar 2023 00:00:00 GMT http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/9379 2023-03-01T00:00:00Z http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/9378 Título: Transferência de estados quânticos em sistemas com desordem correlacionada do tipo trímero Autor: TEIXEIRA, Veronica Alves Primeiro orientador: MORAES, Fernando Jorge Sampaio Abstract: We investigate a Heisenberg quantum chain with correlated disorder for spin-spin coupling. In our model, the spin-spin terms were chosen as a binary distribution. To introduce local correlations we assume that one of the values of our binary disorder distribution always appears in ternary sequences. Using numerical diagonalization, we will investigate the role played by these short-range correlations in the transfer of quantum states between the ends of the magnon chain. The quality of the transfer is observed through the use of standard tools such as fidelity and concurrency and others that confirm such characteristics of the chain inside and outside the channel. Our calculations numerically demonstrate the existence of magnon transfer with good fidelity for some special resonances. We also show what kind of "exchange"interaction between the ends is required for the system to have magnon transfer. Instituição: Universidade Federal Rural de Pernambuco Tipo do documento: Dissertação Thu, 20 Jul 2023 00:00:00 GMT http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/9378 2023-07-20T00:00:00Z http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/9377 Título: Observação experimental de transição de fase schools-shoals em peixe-zebra (Danio rerio) Autor: NEGREIROS NETO, Luis Gomes de Primeiro orientador: BARBOSA, Anderson Luiz da Rocha e Abstract: The collective behavior of active matter encompasses a wide diversity of existing living organisms, ranging from microscopic systems to large-scale systems. Such systems are recognized by their individuals having the ability to transform internal or environmental energy into movement, characterizing them as out-of-equilibrium physical systems. An interesting example to observe is groups of fish that make use of information exchange between the individuals that make up the group to develop energetic, anti-predatory, and food-seeking benefits. From individual decisions, collective patterns of large-scale structures emerge that can be quantitatively analyzed. However, most of the definitions that address the emergence of these patterns, such as the structures of schools and shoals, are based on conceptual criteria of sociability. In this work, we analyze the phase transition of zebrafish groups, through the variation of density. To do so, we used video cameras to capture the position and velocity of zebrafish in a controlled environment. We considered a circular container with a diameter of 50 cm and a water depth of 5 cm, tracking the trajectories of zebrafish, varying the number of individuals N. Then, we investigated the correlation measures of the derivatives of the polarization, aggregation, and Dcentroid parameters used in this work, between the time series for groups of N = 2, 13, and 30 individuals, using the q-gaussian parameter that served to reinforce schools-shoals phase transitions of zebrafish. Thus, we are able to characterize a phase transition between fish groups through the average values of the time series of polarization, aggregation, and D-centroid parameters, influenced by density variation. In addition, we observed variation in the correlation between fish through the fluctuations of these same parameters. With the experimental data of these parameters, we were able to quantify the behavior of schools and shoals during our analyses. Instituição: Universidade Federal Rural de Pernambuco Tipo do documento: Dissertação Fri, 16 Jun 2023 00:00:00 GMT http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/9377 2023-06-16T00:00:00Z