Rotation of quantum liquid without singular vortex lines
  The operator equations for quantum hydrodynamics are discussed and solved in a simple cylindrical geometry. We find a solution with the velocity curl "frozen" into a density of the liquid in the absence of singular vortex lines. The spectrum of small oscillations around this solution is found as a generalization of the standard phonon spectrum, and the stability of the solution is demonstrated. 
Yakov Greenberg and Vladimir Zelevinsky
cond-mat.other nucl-th quant-ph