Self-trapping and flipping of double-charged vortices in optically induced photonic lattices

We report what is believed to be the first observation of self-trapping and charge-flipping of double-charged optical vortices in two-dimensional photonic lattices. Both on- and off-site excitations lead to the formation of rotating quasi-vortex solitons, reversing the topological charges and the direction of rotation through a quadrupole-like transition state. Experimental results are corroborated with numerical simulations.