Non-Hermitian Boundary State Distillation with Lossy Waveguides

Abstract: The hallmark of topological phases is their exotic boundary states. In a series of remarkable experiments it has been shown that classical analogues of these states can be engineered in arrays of coupled optical waveguides given delicately fine-tuned input light. Here, we introduce and experimentally demonstrate a radically different approach in which a pattern of lossy waveguides distills the boundary states for generic, even defocused, input light, thus fully alleviating the need for fine-tuning. Our "topological distillation" approach is remarkably general: the lossy waveguides amount to an effectively non-Hermitian Hamiltonian, and the corresponding time-evolution (propagation of the light in the waveguides) removes the mundane bulk states of any topological (or trivial) band structure while retaining the intriguing boundary states by virtue of being the unique states with the longest life-time. We experimentally demonstrate the power and versatility of our approach by distilling the edge states in photonic graphene, as well as corner and edge states in non-Hermitian Kagome arrays.