13 research outputs found
Gyroscopic motion of superfluid trapped atomic condensates
The gyroscopic motion of a trapped Bose gas containing a vortex is studied.
We model the system as a classical top, as a superposition of coherent
hydrodynamic states, by solution of the Bogoliubov equations, and by
integration of the time-dependent Gross-Pitaevskii equation. The frequency
spectrum of Bogoliubov excitations, including quantum frequency shifts, is
calculated and the quantal precession frequency is found to be consistent with
experimental results, though a small discrepancy exists. The superfluid
precession is found to be well described by the classical and hydrodynamic
models. However the frequency shifts and helical oscillations associated with
vortex bending and twisting require a quantal treatment. In gyroscopic
precession, the vortex excitation modes are the dominant features
giving a vortex kink or bend, while the is found to be the dominant
Kelvin wave associated with vortex twisting.Comment: 18 pages, 7 figures, 1 tabl
Consequence of superfluidity on the expansion of a rotating Bose-Einstein condensate
We study the time evolution of a rotating condensate, that expands after
being suddenly released from the confining trap, by solving the hydrodynamic
equations of irrotational superfluids. For slow initial rotation speeds,
, we find that the condensate's angular velocity increases rapidly
to a maximum value and this is accompanied by a minimum in the deformation of
the condensate in the rotating plane. During the expansion the sample makes a
global rotation of approximately , where the exact value depends on
. This minimum deformation can serve as an easily detectable
signature of superfluidity in a Bose--Einstein condensate.Comment: 4 pages, 3 figures, submitted to PR
Superfluid and Dissipative Dynamics of a Bose-Einstein Condensate in a Periodic Optical Potential
We create Bose-Einstein condensates of 87-rubidium in a static magnetic trap
with a superimposed blue-detuned 1D optical lattice. By displacing the magnetic
trap center we are able to control the condensate evolution. We observe a
change in the frequency of the center-of-mass oscillation in the harmonic
trapping potential, in analogy with an increase in effective mass. For fluid
velocities greater than a local speed of sound, we observe the onset of
dissipative processes up to full removal of the superfluid component. A
parallel simulation study visualizes the dynamics of the BEC and accounts for
the main features of the observed behavior.Comment: 4 pages, including figure
Spectroscopy of Dark Soliton States in Bose-Einstein Condensates
Experimental and numerical studies of the velocity field of dark solitons in
Bose-Einstein condensates are presented. The formation process after phase
imprinting as well as the propagation of the emerging soliton are investigated
using spatially resolved Bragg-spectroscopy of soliton states in Bose-Einstein
condensates of Rubidium87. A comparison of experimental data to results from
numerical simulations of the Gross-Pitaevskii equation clearly identifies the
flux underlying a dark soliton propagating in a Bose-Einstein condensate. The
results allow further optimization of the phase imprinting method for creating
collective exitations of Bose-Einstein condensates.Comment: 14 pages, 9 figure