Almost-Hermitian Random Matrices: Applications to the Theory of Quantum Chaotic Scattering and Beyond

It is generally accepted that statistics of energy levels in closed chaotic quantum systems is adequately described by the theory of Random Hermitian Matrices. Much less is known about properties of "resonances" - generic features of open quantum systems pertinent for understanding of scattering experiments. In the framework of the Heidelberg approach to quantum chaotic scattering open systems are characterized by an effective non-Hermitian random matrix Hamiltonian $\hat{H}_{ef}$. Complex eigenvalues of $\hat{H}_{ef}$ are S-matrix poles (resonances). We show how to find the mean density of these poles (Fyodorov and Sommers) and how to use the effective Hamiltonian to calculate autocorrelations of the photodissociation cross section (Fyodorov and Alhassid). In the second part of the paper we review recent results (Fyodorov, Khoruzhenko and Sommers) on non-Hermitian matrices with independent entries in the regime of weak Non-Hermiticity. This regime describes a crossover from Hermitian matrices characterized by Wigner-Dyson statistics of real eigenvalues to strongly non-Hermitian ones whose complex eigenvalues were studied by Ginibre.