Parity-Time Symmetry and Exceptional Points [Electromagnetic Perspectives]

Recent developments in non-Hermitian physics offer exciting opportunities for a broad range of basic research and engineering applications relevant to the antennas and propagation community. In this article, we offer a tutorial geared toward introducing the unusual electromagnetic phenomena emerging in non-Hermitian systems, with a particular emphasis the subclass of these systems that obey PT symmetry. We first discuss the basic features of ${\hat{P}}$ , ${\hat{T}}$ , and ${\hat{P}}{\hat{T}}$ operators applied to electromagnetic and quantum mechanical phenomena. We then discuss the exotic response of PT-symmetric electromagnetic structures and their opportunities, including the singularities, known as exceptional points ( EPs ), emerging in these systems and their unusual scattering response. We discuss applications, challenges, and potentials in classical and quantum domains.