Observation of non-Hermitian topology from optical loss modulation.

Understanding the interplay of non-Hermiticity and topology is crucial given the intrinsic openness of most natural and engineered systems, and has important ramifications in topological lasers and sensors. Recently, it has been theoretically proposed that topological features could originate solely from a system's non-Hermiticity in photonic platforms. Here we experimentally demonstrate the appearance of non-Hermitian topology exclusively from loss modulation in a photonic system that is topologically trivial in the absence of loss. We do this by implementing a non-Hermitian generalization of an Aubry-André-Harper model with purely imaginary potential in a programmable integrated photonics platform, which allows us to investigate different periodic and quasiperiodic configurations of the model. In both cases, we show the emergence of topological edge modes and explore their resilience to different kinds of disorder. Our work highlights loss engineering as a mechanism to generate topological properties.