Controle coerente em Ãtomos de Rb por manipulaÃÃo da fase de pulsos ultracurtos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

Coherent quantum control aims to drive a quantum system towards a desired final state. Nowadays its study is widely employed to manipulate transitions in atomic systems, to break molecular bonds and to optimize the output of chemical reactions, for instance. In this thesis experimental and theoretical results of partial temporal coherent control in two different two-photon transitions of Rubidium atoms will be presented. The main difference between them is the existence or not of a resonance with an intermediate level. The first transition explored occurs between the 5S and the 7S levels and doesnât present this resonance therefore being the simplest transition studied. On the other hand, the second transition studied 5S-5P-5D presents a one-photon resonance with the intermediate level 5P3/2, which allows the appearance of propagation effects, for instance, not present in the 5S-7S transition. These two transitions were excited by pairs of ultrashort pulses of variable temporal separation. The partial coherent control was achieved through phase manipulation of the electric filed made in one of these two pulses. This phase manipulation was accomplished using a medium to introduce an extra phase, whose amplitude, width and position of the step relative to the pulse spectrum allowed controlling quantum interferences between the several possible quantum paths available to the system. Adequate phase configurations permitted partial or complete annihilation of the two-photon absorption for certain values of temporal delay between the pulses. In the case of the 5S-5P-5D transition, interactions between propagation and phase manipulation effects were detected and deformations due to propagation effects were modified in a controlled way. The theoretical description of these experimental situations was made using second order perturbation theory in a three level model, treating the resonant and non resonant cases separately. Through this theoretical analysis, some special features of the experimental results could be explained. Despite of not obtaining the correct theoretical values to some experimental variables in the case of the transition 5S-5P-5D, this theory made it possible to comprehend the variations in the amplitudes of the central and lateral peaks and the presence of 473 fs periodoscillations correspondent to quantum interferences in the fluorescence signals of this transition. vii Until now there is no record of this kind of partial temporal coherent control in these two transitions

ASSUNTO(S)

fisica controle quÃntico coerente sistema quÃntico

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