Experimental observation of non-Hermitian phase transitions using laser-induced thermoacoustics

Non-Hermitian physics in open systems has garnered significant attention for its exotic phenomena, particularly surrounding exceptional points that offer transformative potential for multifunctional devices. Central to this field are parity-time ( $PT$ ) symmetry-defined by balanced gain and loss-and its counterpart, anti- $PT$ symmetry. However, integrating these divergent concepts into a unified acoustic platform remains an unattainable challenge. In this study, we employ laser-induced thermoacoustics (LIT) to integrate a tunable amplifying component into a non-Hermitian system. By exciting an ultrathin carbon nanotube (CNT) film through laser irradiation, we experimentally observe the phase transitions between $PT$ and anti- $PT$ symmetries. Furthermore, our findings demonstrate the creation of selectable scattering states and the generation of acoustic vortex beams (VBs), facilitating both $PT$ -symmetric scattering and the conversion of topological charges. This acoustically transparent strategy bypasses traditional, path-blocking compensation schemes, offering a versatile framework for controlled non-Hermitian phase transitions in next-generation integrated devices.