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 ($${{\mathcal{P}}}{{\mathcal{T}}}$$) symmetry-defined by balanced gain and loss-and its counterpart, anti-$${{\mathcal{P}}}{{\mathcal{T}}}$$ 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 $${{\mathcal{P}}}{{\mathcal{T}}}$$ and anti-$${{\mathcal{P}}}{{\mathcal{T}}}$$ symmetries. Furthermore, our findings demonstrate the creation of selectable scattering states and the generation of acoustic vortex beams (VBs), facilitating both $${{\mathcal{P}}}{{\mathcal{T}}}$$-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. Non-Hermitian physics offers unique ways to control sound through balanced gain and loss. Here, authors use laser-irradiated carbon nanotube films to create a unified acoustic system that switches between symmetry states, and enables transparent control of vortex beams and topological charges.