"Fun With Vortices in Rotating Optical Lattices"
Volker Schweikhard
JILA
Wednesday, April 26, 2006 11 AM -12 Noon in 430 Birge Hall
Abstract
In my talk I will first give a short introduction to vortices in
rapidly rotating Bose-Einstein condensates (BECs). I will then talk
about our recent experiments on BECs in a rotating two-dimensional optical lattice.
The first set of experiments is concerned with the study of votrex pinning.
A repulsive, co-rotating optical lattice potential generates an array of
pinning sites for vortices. When the optical lattice structure is hexagonal
the angular orientation of the vortext lattices locks to the optical lattice.
Increasing the depth of a square optical lattice induces a structural phase
transition from hexagonal to a square vortex lattice. We study the effects
of slight deviations from commensurate filling of lattice sites with vortices.
Second, I will report on ongoing experiments, where a strong, attractive optical
lattice potential creates a two-dimensional array of separated condensates,
analogous to a Josephson junction array. When ramping down the lattice potential
we observe spontaneous defect creation, as the independent condensates join.
If the potential is static, vortices of clockwise and counterclockwise
circulation are created and rapidly annihilate, whereas in a rotating
potential, "clockwise" vortices are created and remain stable. I will comment
on possible future directions from these experiments.
