| Popis: |
We study the nucleation and dynamics of vortices in rotating lattice potentials where weakly linked condensates are formed with each condensate exhibiting an almost axial symmetry. Due to such a symmetry, the on-site phases acquire a linear dependence on the coordinates as a result of the rotation, which allows us to predict the position of vortices along the low density paths that separate the sites. We first show that, for a system of atoms loaded in a four-site square lattice potential, subject to a constant rotation frequency, the analytical expression that we obtain for the positions of vortices of the stationary arrays accurately reproduces the full three-dimensional Gross-Pitaevskii results. We then study the time-dependent vortex nucleation process when a linear ramp of the rotation frequency is applied to a lattice with sixteen sites. We develop a formula for the number of nucleated vortices which turns to have a linear dependence on the rotation frequency with a smaller slope than that of the standard estimate which is valid in absence of the lattice. From time-dependent Gross-Pitaevskii simulations we further find that the on-site populations remain almost constant during the time evolution instead of spreading outwards, as expected from the action of the centrifugal force. Therefore, the time-dependent phase difference between neighboring sites acquires a running behavior typical of a self-trapping regime. We finally show that, in accordance with our predictions, this fast phase-difference evolution provokes a rapid vortex motion inside the lattice. Our analytical expressions may be useful for describing other vortex processes in systems with the same on-site axial symmetry. |
