Non-Abelian effects in dissipative photonic topological lattices

Topology is central to phenomena that arise in a variety of fields, ranging from quantum field theory to quantum information science to condensed matter physics. Recently, the study of topology has been extended to open systems, leading to a plethora of intriguing effects such as topological lasing, exceptional surfaces, as well as the non-Hermitian bulk-boundary correspondence. Here, we show that resonator networks with dissipative couplings can be governed by matrix-valued modified Wilson lines, leading to non-Abelian effects. This is in contrast to conservative Hamiltonians exhibiting non-degenerate energy levels, where the geometric properties of the Bloch eigenstates are typically characterized by scalar Berry phases. We experimentally measure geometric phases and demonstrate non-Abelian effects in a dissipatively-coupled network of time-multiplexed photonic resonators. Our results point to new ways in which the combined effect of topology and engineered dissipation can lead to non-Abelian topological phenomena.