Localization of light in a parity-time-symmetric quasi-periodic lattice.

We address the propagation of light in a parity-time (PT) symmetric quasi-periodic optical lattice. We show that the PT-symmetry breaking threshold of the system depends on the relative strength of two simple lattices forming quasi-periodic structure. The increase of the imaginary part of such structure leads to a dynamical phase transition from delocalization to re-localization for all eigenmodes. The nontrivial interplay between PT-symmetry breaking and the delocalization-localization transition in the system opens new prospects for the manipulation of dynamical evolution of light beams.