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

Abstract

We report on the experimental observation of vortex formation and production of tangled vortex distribution in an atomic BEC of 87 Rb 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.

Quantum turbulence and thermodynamics on a trapped Bose-Einstein condensate

“…The first evidence of the onset of QT in a (dilute gas) BEC were recently reported by our research group (27)(28)(29)(30)(31). Most of the results presented in this thesis are related to that observation.…”

Mechanism of vortices generation for a trapped superfluid under oscillatory excitation

“…By increasing the values of both parameters we were able to produce vortices, which grew in number with the amplitude and/or the excitation elapsed time. Further information can be found elsewhere [1,2,19,20].…”

Comportamento de condensados de Bose-Einstein aprisionados, na presença de vórtices e modos coletivos

“…24 Experimental realizations of condensed alkali-metal atoms confined by more general timedependent potentials allowed the observation not only of vortex lattices but also of quantum turbulence. 7,9,10,20 Since quantum turbulence is characterized by the presence of a self-interacting tangle of quantized vortices, the correct understanding of dynamics, formation, and stability of vortices has shown to be of paramount importance being the subject of many theoretical works. [25][26][27] In particular, the role of acoustic excitations generated by decaying multi-charged vortices in the development of turbulence is still an open question.…”

“…We can make the following transformation in time scale 10) in order to rewrite (6.8) into a more familiar expression, which is the coupled Mathieu equation: The basic idea of this theory is that if a linear differential equation has periodic coefficients and periodic boundary conditions, consequently the solutions will also be a periodic function times an exponentially increasing (decreasing) function. Thus states, that are solutions of Mathieu equation for any pair of A and Q, can be expressed as 12) where ⌘ is called as characteristic exponent being a constant depending on A and Q, and P (⌧ )…”

“…5 Experiments have observed quantum turbulence due to entanglement of vortices which is still an opened question in physics. [6][7][8][9][10] It has been demonstrated the controlled creation of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose-Einstein condensate, where monopoles are identified at the termini of vortex lines within the condensate. 11 I will make a brief introduction to the Bose-Einstein condensates, and how vortices are nucleated inside them, furthermore I shall expose the system that is the subject of this thesis and our objectives.…”