Pseudovorticity of 2+1D optical solitons

In the hydrodynamic representation of a quantum fluid or optical field, vorticity vanishes wherever the phase is well defined, and is instead localized at phase singularities, or quantum vortices. Pseudovorticity, by contrast, characterizes local rotational structures, even in regions without singularities or net orbital angular momentum. We study both experimentally and numerically pseudovorticity in photorefractive solitons and show that a detailed phase and amplitude analysis unveils a complex rotational flow dynamic: bright 2+1D solitons are found to carry a pseudovorticity dipole, while quadrupoles emerge in soliton fusion. The phenomenon, also explained using geometrical considerations, suggests a general picture according to which stable high-dimensional solitons naturally carry a hierarchy of pseudovorticity multipoles, encoded in the local perturbed phase and amplitude.