Modulation instability in a binary Bose-Einstein condensate

• Ano de defesa: 2025
• Autor(a) principal: Gaspar, Pedro Minarelli
• 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: Binary mixture; Bose-Einstein condensate; Condensado de Bose-Einstein; Instabilidade modulacional; Mistura binária; Modulation instability; Sódio; Sodium
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/76/76134/tde-23092025-084325/

If two immiscible components are set together, they tend to phase-separate. This demixing dynamic is not always smooth, and in some cases – such as oil and water demixing – specific patterns and structures emerge before the complete segregation. The onset of these structures is described as a hydrodynamic instability, where a small fluctuation in the system is amplified, leading to specific domain formations. Such instabilities are also predicted and observed in quantum superfluids, such as liquid helium and atomic Bose- Einstein condensates (BECs). In this thesis, we first produce an almost pure sodium BEC in an optical trap, where a μ–wave pulse transfer part of the atoms from the hyperfine state |F = 1,mF = −1⟩ to |F = 2,mF = −2⟩. This initially overlapped mixture is immiscible and, during the demixing dynamics, we have observed the formation of alternating concentric shells associated to the onset of a modulation instability. Our analysis was able to identify the exponential increase of the pattern formation, characteristic of an instability, and estimate its time and length scales. In addition, the instrumentation developed in this project to produce the binary BEC opened up the possibility for further studies in the context of phase-separation and spin mixtures.