Designing topological edge states in bacterial active matter

While active matter is intrinsically nonequilibrium and fluctuating, the emergence of topologically protected edge states with characteristic transport has been theoretically proposed using the methodology of wavenumber topology. However, experimental realization remains largely unexplored, having been limited to systems composed of chiral active particles. Extending such edge states to geometrically structured systems offers new routes to realize and control topological transport in active matter. Here, using microfabricated geometrical structures inspired by theory, we realized topological edge states in dense bacterial suspension. The structures consist of circular wells connected by ratchet-shaped channels that induce unidirectional flow. In a kagome network with directional connections, we found edge localization of bacterial density, resulting from rectified collective flow driven by the network geometry. By tuning the geometry of the microfabricated devices, we identified key geometrical features for the emergence of edge states. Our experimental findings will pave the way toward establishing a foundation for controlled topological transport in such active matter.