Experimental realization of higher-dimensional non-Hermitian acoustic lattices

We designed and implemented an active acoustic crystal to experimentally realize higher-dimensional non-Hermitian lattices. This platform enables precise tuning of both onsite potentials and hoppings using active components comprising microphones, loudspeakers, and a centralized digital controller. As a first demonstration, we implemented a nonreciprocal non-Hermitian Kagome lattice and used both real and complex frequency excitations to observe the higher-order non-Hermitian skin effect. In the topologically nontrivial phase, acoustic energy was observed to localize at a corner of the lattice, even when the source was positioned far from that corner. Subsequently, we realized both nonreciprocal and reciprocal two-dimensional single-band non-Hermitian lattices. Through direct measurements of energy spectra and eigenstates, we experimentally confirmed that energy spectra are highly sensitive to boundary conditions in both cases but are influenced by lattice geometry only in reciprocal systems. Moreover, we observed significant skewness between the left and right eigenstates in nonreciprocal lattices, while in reciprocal lattices, the eigenstates were nearly identical. These experimental results align well with theoretical predictions, validating the effectiveness of our platform. This versatile experimental setup holds broad potential for advancing studies in non-Hermitian physics and exploring uncharted theoretical predictions.