This is the 20th of a series of annual international meetings that was initiated by Miloslav Znojil in 2003. The first two of these meetings were held in Prague (Czech Republic) in 2003 and 2004. These followed by larger gatherings in Istanbul (2005 & 2013), Stellenbosch (South Africa), Bologna (Italy), London (UK), Benasque (Spain), Mumbai (India), Hangzhu (China), Dresden (Germany), Paris (France), Jerusalem (Israel), Satif (Algeria), Palermo (Italy), Kyoto (Japan), Bad Honnef (Germany), Bangalor (India), and Sania (China).
These meetings were initially attended by a small group of experts working on various aspects of pseudo-Hermitian and PT-symmetric Hamiltonians. Later they attracted the attention of a more diverse groups of physicists and mathematicians interested in the study of non-Hermitian operators and their physical applications.
Since 2007 there has been a growing interest in the theoretical and experimental studies of the exceptional points associated with PT-symmetry breaking in PT-symmetric optical systems and the optical spectral singularities and their time-reversal dual that respectively yield threshold lasing and coherent perfect absorption of light. These have motivated the study of scattering aspects of complex potentials and led to the discovery of the phenomenon of unidirectional invisibility, anti-PT-symmetry, and their physical realizations. More recently, there has been substantial progress towards finding physical applications of exceptional points in condensed matter systems. PHHQP20 intends to cover these and other more traditional topics of this series of workshops such as the mathematical and physical aspects of pseud-Hermitian operators, indefinite-metric quantum theories, open quantum systems, and resonances.