Exceptional Points

Abstract

This Chapter overviews the physics of non-Hermitian degeneracies at the so-called exceptional points. We consequentially give an introduction to theoretical aspects of non-Hermitian physics and fundamentals of exceptional points supporting our conclusions with specific examples borrowed from optics and photonics studies. In particular, we consider exceptional points on the ground of both passive components and active media containing loss and gain. In the latter case, the optical PT symmetry, an especially fruitful notion, is feasible. Exceptional points in PT-symmetric systems can be also defined as a border between symmetric and symmetry-broken phases. The Chapter embraces discussion of topological properties of exceptional points observed under static and dynamic encircling and the basics of enhanced sensing near exceptional points able to detect single molecules. Finally, we show that the exceptional points are useful for studying the strong light-matter coupling in polariton physics.