What is the resonant state in open quantum systems?

Abstract The article reviews the theory of open quantum system from a perspective non-Hermiticity that emerges environment with an infinite number degrees freedom. produces resonant states complex eigenvalues, resulting in peak structures scattering amplitudes and transport coefficients. After introducing definition we answer typical questions regarding systems. What is physical meaning eigenmomenta eigenenergies? How why do break time-reversal symmetry observes? Can make probabilistic interpretation diverging wave functions? divergence We also present alternative way finding states, namely Feshbach formalism, which eliminate environmental In this attribute to introduction retarded advanced Green’s functions.