J. A. Seman

Emergence of Turbulence in an Oscillating Bose-Einstein Condensate

We report on the experimental observation of vortex tangles in an atomic Bose-Einstein condensate (BEC) of ;{87}Rb atoms when an external oscillatory perturbation is introduced in the trap. The vortex tangle configuration is a signature of the presence of a turbulent regime in the cloud. We also show that this turbulent cloud suppresses the aspect ratio inversion typically observed in quantum degenerate bosonic gases during free expansion. Instead, the cloud expands keeping the ratio between their axis constant. Turbulence in atomic superfluids may constitute an alternative system to investigate decay mechanisms as well as to test fundamental theoretical aspects in this field.

Observation of vortex formation in an oscillating trapped Bose-Einstein condensate

We report on the observation of vortex formation in a Bose-Einstein condensate of

Route to turbulence in a trapped Bose-Einstein condensate

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Generation of nonground-state Bose-Einstein condensates by modulating atomic interactions

atoms. Vortices are generated by superimposing an oscillating excitation to the trapping potential introduced by an external magnetic field. For small amplitudes of the external excitation field we observe a bending of the cloud axis. Increasing the amplitude we observe formation of a growing number of vortices in the sample. Shot-to-shot variations in both vortex number and position within the condensed cloud are observed, probably due to the intrinsic vortex nucleation dynamics. We discuss the possible formation of vortices and antivortices in the sample as well as possible mechanisms for vortex nucleation.

Generation of Vortices and Observation of Quantum Turbulence in an Oscillating Bose-Einstein Condensate

We have studied a Bose-Einstein condensate of 87Rb atoms under an oscillatory excitation. For a fixed frequency of excitation, we have explored how the values of amplitude and time of excitation must be combined in order to produce quantum turbulence in the condensate. Depending on the combination of these parameters different behaviors are observed in the sample. For the lowest values of time and amplitude of excitation, we observe a bending of the main axis of the cloud. Increasing the amplitude of excitation we observe an increasing number of vortices. The vortex state can evolve into the turbulent regime if the parameters of excitation are driven up to a certain set of combinations. If the value of the parameters of these combinations is exceeded, all vorticity disappears and the condensate enters into a different regime which we have identified as the granular phase. Our results are summarized in a diagram of amplitude versus time of excitation in which the different structures can be identified. We also present numerical simulations of the Gross-Pitaevskii equation which support our observations.

Finite temperature correction to the Thomas–Fermi approximation for a Bose–Einstein condensate: comparison between theory and experiment

A technique is proposed for creating nonground-state Bose-Einstein condensates in a trapping potential by means of the temporal modulation of atomic interactions. Applying a time-dependent spatially homogeneous magnetic field modifies the atomic scattering length. An alternating modulation of the scattering length excites the condensate, which, under special conditions, can be transferred to an excited nonlinear coherent mode. It is shown that there occurs a phase-transition-like behavior in the time-averaged population imbalance between the ground and excited states. The application of the suggested technique to realistic experimental conditions is analyzed and it is shown that the considered effect can be realized for experimentally available condensates.

Bose-Einstein condensation in 87Rb: characterization of the Brazilian experiment

We report on the experimental observation of vortex formation and production of tangled vortex distribution in an atomic BEC of 87Rb atoms submitted to an external oscillatory perturbation. The oscillatory perturbations start by exciting quadrupolar and scissors modes of the condensate. Then regular vortices are observed finally evolving to a vortex tangle configuration. The vortex tangle is a signature of the presence of a turbulent regime in the cloud. We also show that this turbulent cloud has suppression of the aspect ratio inversion typically observed in quantum degenerate bosonic gases during free expansion.

Turbulence in a trapped Bose-Einstein condensate

We observe experimentally a deviation of the radius of a Bose–Einstein condensate from the standard Thomas–Fermi prediction, after free expansion, as a function of temperature. A modified Hartree–Fock model is used to explain the observations, mainly based on the influence of the thermal cloud on the condensate cloud.

Evaporation in atomic traps: A simple approach

We describe the experimental apparatus and the methods to achieve Bose-Einstein condensation in 87Rb atoms. Atoms are first laser cooled in a standard double magneto-optical trap setup and then transferred into a QUIC trap. The system is brought to quantum degeneracy selectively removing the hottest atoms from the trap by radio-frequency radiation. We also present the main theoretical aspects of the Bose-Einstein condensation phenomena in atomic gases.

Introduction to the Basic-Concepts of Bose-Einstein Condensation

We have used an atomic 87Rb BEC to study the emergence of quantum turbulence. The application of an external oscillating magnetic field gradient is used to nucleate vortices and anti-vortices spread over the cloud, in many directions, setting up the conditions for the turbulent regime to arise. Once the turbulence is established one may study it in a variety of its different aspects and we will present and discuss a few of these possibilities.