Guiding-center dynamics of vortex dipoles in Bose-Einstein condensates
  A quantized vortex dipole is the simplest vortex molecule, comprising two counter-circulating vortex lines in a superfluid. Although vortex dipoles are endemic in two-dimensional superfluids, the precise details of their dynamics have remained largely unexplored. We present here several striking observations of vortex dipoles in dilute-gas Bose-Einstein condensates, and develop a vortex-particle model that generates vortex line trajectories that are in good agreement with the experimental data. Interestingly, these diverse trajectories exhibit essentially identical quasi-periodic behavior, in which the vortex lines undergo stable epicyclic orbits. 
S. Middelkamp, P.J. Torres, P.G. Kevrekidis, D.J. Frantzeskakis, R.   Carretero-Gonzalez, P. Schmelcher, D.V. Freilich, and ...
cond-mat.quant-gas cond-mat.soft nlin.PS