Manipulating non-reciprocity in a two-dimensional magnetic quantum walk

Abstract: Non-reciprocity is an important topic in fundamental physics and quantum-device design, as much effort has been devoted to its engineering and manipulation. Here we experimentally demonstrate non-reciprocal transport in a two-dimensional quantum walk of photons, where the directional propagation is highly tunable through dissipation and synthetic magnetic flux. The non-reciprocal dynamics hereof is a manifestation of the non-Hermitian skin effect, with its direction continuously adjustable through the photon-loss parameters. By contrast, the synthetic flux originates from an engineered geometric phase, which competes with the non-Hermitian skin effect through magnetic confinement. We further demonstrate how the non-reciprocity and synthetic flux impact the dynamics of the Floquet topological edge modes along an engineered boundary. Our results exemplify an intriguing strategy for achieving tunable non-reciprocal transport, highlighting the interplay of non-Hermiticity and gauge fields in quantum systems of higher dimensions.