18 research outputs found
Route to turbulence in a trapped Bose-Einstein condensate
We have studied a Bose-Einstein condensate of 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.Comment: 6 pages, 3 figure
Three-vortex configurations in trapped Bose-Einstein condensates
We report on the creation of three-vortex clusters in a
Bose-Einstein condensate by oscillatory excitation of the condensate. This
procedure can create vortices of both circulation, so that we are able to
create several types of vortex clusters using the same mechanism. The
three-vortex configurations are dominated by two types, namely, an
equilateral-triangle arrangement and a linear arrangement. We interpret these
most stable configurations respectively as three vortices with the same
circulation, and as a vortex-antivortex-vortex cluster. The linear
configurations are very likely the first experimental signatures of predicted
stationary vortex clusters.Comment: 4 pages, 4 figure
Equation of state for a trapped quantum gas: remnant of zero-point energy effects
The study of the thermodynamic properties of trapped gases has attracted great attention during the last few years and can be used as a tool to characterize such clouds in the presence of other phenomena. Here, we obtain an equation of state for a harmonically trapped Bose–Einstein condensate taking the limit of by means of global themodynamic variables. These variables allow us to explore limits in which the standard thermodynamics are not defined. Our results are taken in the high density limit, and the extrapolation for is done later. Even in this situation, we qualitatively observe the well known existence of a zero-point energy for harmonic potentials in which the determination of conjugated variables is limited by the quantum nature of the system