Nonreciprocal and topological phenomena in active optomechanical meta-matter

We create multi-mode nano-optomechanical networks in which the interactions between mechanical modes are induced and fully reconfigured through time-modulated radiation pressure forces. We study the nonreciprocal and topological states that emerge from controlled breaking of time-reversal symmetry and Hermiticity in such laser-driven optomechanical metamaterials. We demonstrate unidirectional flow of sound and the emergence of the quantum Hall effect in small networks of nanomechanical resonators. We uncover that broken time-reversal symmetry can influence the thermodynamic efficiency of optomechanical refrigeration. Moreover, we realize the bosonic Kitaev chain; the bosonic counterpart of the fermionic model that famously predicts Majorana zero modes. This establishes a non-Hermitian topological phase in which a unique form of directional amplification emerges as a physical phenomenon that links to the chain’s topological nature. This behavior has intriguing implications for signal processing and enhanced sensing performance.