Realization of encircling the exceptional point in non-Hermitian acoustic waveguide coupler

The encirclement of exceptional points (EPs) in parametric space has been realized in optical waveguides, microwave cavities, nitrogen-vacancy centers, and so on. However, it often suffers from complex gain–loss manipulation. An acoustic platform to realize the evolution encircling the EP is highly desirable. In this work, an unclosed evolution protocol is proposed, which consists of parallel coupling and buffering branches and evolves through five distinct stages. Buffering the variation of Hamiltonian, inducing the transition to a low energy state, the evolution with favorable adiabaticity guarantees the EP encircling no longer depends on the precise loss manipulation. A non-Hermitian acoustic waveguide coupler (AWC), which is composed of combined cavities and air slit arrays, is presented to realize the encirclement. Experimental results of chiral phase conversion in a 0.5 m long AWC, spanning a broad bandwidth from 9.5 to 17.5 kHz, confirm the simplicity and effectiveness of state evolution encircling the EP. This work paves the way for AWC as a platform for non-Hermitian topological physics and facilitates the practical deployment of acoustic devices.