Parity-Time Symmetry and Exceptional Points [Electromagnetic Perspectives]
Alex Krasnok, Nikita Nefedkin, Andrea Alù
Abstract
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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\hat{P}}$</tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\hat{T}}$</tex-math></inline-formula> , and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\hat{P}}{\hat{T}}$</tex-math></inline-formula> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">exceptional points</i> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EPs</i> ), emerging in these systems and their unusual scattering response. We discuss applications, challenges, and potentials in classical and quantum domains.