Spontaneous Symmetry Breaking in Photonic Lattices: Theory and   Experiment
  We examine an example of spontaneous symmetry breaking in a double-well waveguide with a symmetric potential. The ground state of the system beyond a critical power becomes asymmetric. The effect is illustrated numerically, and quantitatively analyzed via a Galerkin truncation that clearly shows the bifurcation from a symmetric to an asymmetric steady state. This phenomenon is also demonstrated experimentally when a probe beam is launched appropriately into an optically induced photonic lattice in a photorefractive material. 
P.G. Kevrekidis, Zhigang Chen, B.A. Malomed, D.J. Frantzeskakis and   M.I. Weinstein