Topological transfer of multidimensional states in phononic crystals

Topological pump is a promising route to realize robust transfer between the states of different dimensions. Of special interest is the hybrid-order topological pump, which exhibits a transfer of bulk, edge, and corner states simultaneously. To date, however, hybrid-order topological pump remains largely unexplored, and the associated intriguing state transfer has not been observed in continuous transport processes. Here we report the topological corner-edge-bulk-edge-corner state transfer, which derives from hybrid-order topological pump linked to second-order topology. The topological transfer of multidimensional states is directly observed by spatially visualizing the continuous sound transport, and its topological robustness is observed in the path with defects. Furthermore, by breaking the adiabatic limitation, states localized at one corner can be switched into the states localized at two spatially separated corners, as observed in our acoustic experiments. More interestingly, the coexistence of first-order, higher-order and hybrid-order topological pumps is achieved by modifying the phononic crystal profile (e.g., cutting the right edge of the finite system), which gives more fascinating topological state transfers (e.g., corner-edge/bulk-corner state transfers). Our results open a new path towards unveiling more complex topological pumps and provide an efficient way to manipulate acoustic waves.