Laser-induced Rotation of a Trapped Bose-Einstein Condensate
A Bose-Einstein condensate (BEC) is a state of matter where all atoms occupy the same state A vortex state is a state in which these atoms collectively rotate around a line (vortex core). For simplicity this line is chosen to coincide with the z-axis.
To create a vortex state from a resting condensate one obviously has to transfer angular momentum to the atoms. We examined whether this can be achieved by using laser light. One proposal was based on four traveling laser beams in the x-y-plane.
The arrangement of the laser beams can be designed so that the atoms experience a rotating homogeneous force which of course can transfer angular momentum to the condensate. If the rotation frequency is in resonance with the transition between the ground state and the first vortex state this transfer can be very effective.
However, in a harmonic trap the condensate does not form a vortex state but rather rotates as a whole with increasing radius around the trap center (much like a billiard ball in a bowl).
You may be surprised that no vortex is created. In another paper we have resolved this puzzle.