Observation of Aharonov‐Bohm‐Caged Directional Amplification in Acoustic Lattices

Recently, substantial efforts have been made to control the non‐Hermitian skin effect (NHSE), a prominent phenomenon that features a macroscopic number of eigenstates accumulating toward open boundaries. Aharonov‐Bohm (AB) caging, as another fascinating wave localization mechanism, competes with NHSE and offers a unique way to control NHSE. Here, an experimental observation of AB‐caged directional amplification in one‐dimensional rhombic non‐Hermitian acoustic lattices is reported. The key experimental elements, including nonreciprocal couplings and gauge fluxes that are challenging in magnetic‐inert acoustic systems, are carefully implemented with active and reconfigurable feedback circuits. The results reveal a continuous suppression of the skin response with gauge flux due to the contracted point‐gap area. More intriguingly, at π‐flux, the unidirectional sound pumping is forbidden by AB caging, where all bands become completely flat and the states are compactly localized around the sound source. The study sheds new light on the interplay between the non‐Hermiticity and gauge fields, with potential implications for wave control and transport.