Some Perspectives on Non-Hermitian Metamaterials and Metasurfaces

Originally inspired by quantum-physics concepts such as parity-time symmetry, non-Hermitian metastructures characterized by spatially modulated distributions of loss and gain are eliciting a growing attention in optics and photonics. Within this framework, contrary to conventional wisdom, losses are not considered as second-order, detrimental effects to be minimized or compensated for, and their interplay with gain is instead instrumental for engineering unconventional light-matter interaction effects. Here, we compactly review some recent developments and perspectives in this fascinating research area.