9 research outputs found
Momentum distribution of Vinen turbulence in trapped atomic Bose-Einstein condensates
The decay of multicharged vortices in trapped Bose-Einstein condensates may
lead to a disordered vortex state consistent with the Vinen regime of
turbulence, characterized by an absence of large-scale flow and an
incompressible kinetic energy spectrum . In this work, we
study numerically the dynamics of a three-dimensional harmonically trapped
Bose-Einstein condensate excited to a Vinen regime of turbulence through the
decay of two doubly-charged vortices. First, we study the momentum distribution
and observe the emergence of a power-law behavior
consistent with the coexistence of wave turbulence. We also study the kinetic
energy and particle fluxes, which allows us to identify a direct particle
cascade associated with the turbulent stage.Comment: 5 pages, 2 figure
Phononic bright and dark states: Investigating multi-mode light-matter interactions with a single trapped ion
Interference underpins some of the most practical and impactful properties of
both the classical and quantum worlds. In this work we experimentally
investigate a new formalism to describe interference effects, based on
collective states which have enhanced or suppressed coupling to a two-level
system. We employ a single trapped ion, whose electronic state is coupled to
two of the ion's motional modes in order to simulate a multi-mode light-matter
interaction. We observe the emergence of phononic bright and dark states for
both a single phonon and a superposition of coherent states and demonstrate
that a view of interference which is based solely on their decomposition in the
collective basis is able to intuitively describe their coupling to a single
atom. This work also marks the first time that multi-mode bright and dark
states have been formed with the bounded motion of a single trapped ion and we
highlight the potential of the methods discussed here for use in quantum
information processing.Comment: 7 + 5 pages, 6 + 4 figure
Turbulência quântica e vórtices multicarregados em superfluidos atômicos aprisionados
In this thesis, we numerically investigate quantum turbulence in trapped atomic Bose-Einstein condensates (BECs). We first discuss the appropriate qualitative characterization of turbulence in these systems, showing the limitation of analogies with classical hydrodynamics and turbulence in large superfluid Helium experiments. Due to their lack of available length scales, our investigated systems can only fit the ultraquantum (or Vinen) type of quantum turbulence. Secondly, we propose experimentally feasible schemes for more controlled investigations of turbulence making use of dynamical instability of multicharged vortices as an onset for complex vortex dynamics. In two dimensions, our suggested scheme allows control over vortex polarization in the harmonically trapped system. This setup is then used to study how turbulence decays in such a scenario, through the phenomenological modeling of a vortex-number rate equation. As a consequence, we were able to identify that vortex annihilation in these trapped systems happens through a four-vortex process. For three dimensions, we have first provided a study on the decay of a quadruply-charged vortex, also in a harmonically trapped BEC. Having this setting as a comparison point, we propose a quasi-isotropic turbulent system, starting from a phase-imprinted initial state of two doubly-charged, anti-parallel vortices. The vortex turbulence arisen from such configuration was shown to agree with the Vinen turbulent regime, after we characterized specific features of its decay, such as the energy spectrum [E(k) ∼ k1] and the time evolution of the vortex-line density [L(t) ∼ t1]. Although these features have been frequently verified in the context of superfluid Helium turbulence, here this identification was for the first time done for realistic, trapped atomic BECs.Nesta tese, investigamos numericamente a turbulência quântica em condensados de Bose- Einstein (BECs) aprisionados. Discutimos, inicialmente, a caracterização qualitativa apropriada para estes sistemas, mostrando a limitação de analogias tipicamente feitas com hidrodinâmica clássica e turbulência em grandes sistemas com Hélio superfluido. Devido às suas limitadas escalas espaciais, os sistemas investigados somente podem exibir o tipo de turbulência conhecida como ultra-quântica (ou de Vinen). Em seguida, propomos sistemas experimentalmente factíveis que permitem investigações mais controladas da turbulência, fazendo uso da instabilidade dinâmica de vórtices multi-carregados como ponto de partida para geração de dinâmicas complexas. Em duas dimensões, nossa proposta permite controle sobre a polarização de vórtices em sistemas aprisionados em potencial harmônico. Este arranjo é então utilizado no estudo do decaimento da turbulência nesse contexto, através de um modelo fenomenológico para equação que descreve a taxa de variação do número de vórtices. Como consequência, pudemos verificar que a aniquilação de vórtices dá-se através de um processo que envolve quatro vórtices. Em três dimensões, apresentamos um estudo do decaimento de um vórtice de carga topológica quatro, também em potencial harmônico. Mantendo em mente esse sistema a título de comparação, propomos um cenário turbulento, quase-isotrópico, partindo de um estado inicial formado por dois vórtices duplamente carregados, mas orientados anti-paralelamente. Verificamos que a turbulência decorrente desse arranjo coincide com a regime de Vinen analisando características do seu decaimento, especificamente obtendo o espectro de energia [E(k) ∼ k1] e evolução temporal da densidade de linhas de vórtices [L(t) ∼ t1]. Apesar de que essas características são comumente encontradas no contexto de Hélio superfluido, apresentamos pela primeira vez essa identificação no cenário realístico de BEC aprisionados
Decoherence of gaussian packet in a harmonic potential
Orientador: Amir Ordacgi CaldeiraDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb WataghinResumo: Nesse trabalho estudamos o problema quântico dissipativo de um pacote gaussiano aprisionado num potencial harmônico. Seguimos uma abordagem fenomenológica de dissipação, à luz do modelo Caldeira-Leggett, onde o ambiente é caracterizado por um banho osciladores harmônicos. Sendo um dos efeitos do acoplamento com o banho transformar o pacote inicialmente puro em uma mistura estatística num processo de decorrência, estimamos o tempo característico em que isso ocorre em diferentes regimes de temperatura e acoplamentoAbstract: In this work we have studied the quantum dissipative problem of a gaussian packet under the influence of a harmonic potential. A phenomenological approach to dissipation is taken, in the light of the Caldeira-Leggett model, in which the environment is characterized by a bath of harmonic oscillators. As one of the effects of the coupling to the bath being leading the initially pure packet into a statistical mixture, we estimate the characteristic time elapsed for this to occur in different regimes of temperature and couplingMestradoFísicaMestre em Físic
Generating long-lived entangled states with free-space collective spontaneous emission
International audienceConsidering the paradigmatic case of a cloud of two-level atoms interacting through common vacuum modes, we show how cooperative spontaneous emission, which is at the origin of superradiance, leads the system to long-lived entangled states at late times. These subradiant modes are characterized by an entanglement between all particles, independently of their geometrical configuration. While there is no threshold on the interaction strength necessary to entangle all particles, stronger interactions lead to longer-lived entanglement
Field and intensity correlations: the Siegert relation from stars to quantum emitters
The Siegert relation relates field and intensity temporal correlations. After a historical review of the Siegert relation and the Hanbury Brown and Twiss effect, we discuss the validity of this relation in two different domains. We first show that this relation can be used in astrophysics to determine the fundamental parameters of stars, and that it is especially important for the observation with stellar emission lines. Second, we verify the validity of this relation for moving quantum scatterers illuminated by a strong driving field
Field and intensity correlations: the Siegert relation from stars to quantum emitters
The Siegert relation relates field and intensity temporal correlations. After a historical review of the Siegert relation and the Hanbury Brown and Twiss effect, we discuss the validity of this relation in two different domains. We first show that this relation can be used in astrophysics to determine the fundamental parameters of stars, and that it is especially important for the observation with stellar emission lines. Second, we verify the validity of this relation for moving quantum scatterers illuminated by a strong driving field
Field and intensity correlations: the Siegert relation from stars to quantum emitters
The Siegert relation relates field and intensity temporal correlations. After a historical review of the Siegert relation and the Hanbury Brown and Twiss effect, we discuss the validity of this relation in two different domains. We first show that this relation can be used in astrophysics to determine the fundamental parameters of stars, and that it is especially important for the observation with stellar emission lines. Second, we verify the validity of this relation for moving quantum scatterers illuminated by a strong driving field