Excitation of Bose-Einstein Condensates through the separate fields technique

• Ano de defesa: 2024
• Autor(a) principal: Machado, Leandro Alvares
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Bose-Einstein condensate; Collective modes; Condensado de Bose-Einstein; Franjas de Ramsey; Modos coletivos; Quantum turbulence; Ramsey fringes; Turbulência quântica
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/76/76134/tde-16042025-145354/

In this work, we propose a new approach to excite a Bose-Einstein condensate by introducing perturbations to the trapping potential through the separate fields technique, originally introduced by Norman F. Ramsey as an enhancement of I. I. Rabi method used for studying spin magnetic resonances. We employed the variational method based on the Thomas-Fermi wave function Ansatz to obtain dynamical equations governing the radii of a Bose-Einstein condensate when under external perturbations. The obtained dynamical equations allow us to construct the resonance curves for the collective modes of Bose- Einstein condensates, specifically focusing on the dipole, quadrupole and breathing modes. We observed that depending on whether the external signal is modulated by the Rabi or Ramsey procedure, the system behaves differently due to its inherent coherence, that reflects on the resonance curve of the collective modes, giving rise to the Ramsey fringes in a clear interference pattern, enabling a more precise frequency measurement. With the insights offered by the variational method, we introduced an alternative model to describe the dynamics of collective modes based on a three-level system, which proved to be consistent with the variational model. Moreover, the three-level model provided a framework for fostering the idea of coherent control by manipulating the population associated with collective modes through the application of perturbation pulses, such as a π-pulse and a π/2-pulse. This concept draws an analogy with interferometry in atoms. As a complementary study, we numerically solved the three-dimensional Gross-Pitaevskii equation in order to take into account other types of potential fluctuations not considered in both variational and three-level models. Finally, to present ongoing analyses and their perspectives, we used the Rabi excitation protocol to study how the external modulation leads to specific routes in terms of generation of quantum turbulence. By examining the behavior of the system under various excitations, this research offers new perspectives in the non-equilibrium BEC field, fostering a deeper understanding of BEC dynamics and its potential applications in quantum interference and turbulence studies.