Observation of non-Hermitian topology and its bulk-edge correspondence

Topological edge modes and the bulk-edge correspondence has enabled the creation of robust electronic, electromagnetic and mechanical transport properties across a wide range of systems, from cold atoms to metamaterials, active matter and geophysical flows. Recently, in the advent of non-Hermitian topological systems novel topological phases have been introduced. However, whether such phases can be experimentally observed, and what their properties are, have remained open questions. Here, we discover and observe a novel form of bulk-edge correspondence for non-Hermitian topological phases. We find that a change in the bulk non-Hermitian topological invariant corresponds to a change of localization of the topological edge mode. Using a quantum-to-classical analogy, we create a mechanical metamaterial with non-reciprocal interactions, in which we observe experimentally the predicted bulk-edge correspondence, demonstrating its robustness. Our results have a major impact on the field of non-Hermitian topology and boost metamaterials by opening new avenues to manipulate waves in unprecedented fashions.

Ref: Ananya Ghatak, Martin Brandenbourger, Jasper van Wezel and Corentin Coulais, arXiv:1907.11619 (2019).