A non-Hermitian quantum mechanics approach for extracting and emulating continuum physics based on bound-state-like calculations

Abstract: This work develops a new method for computing a finite quantum system's continuum states and observables by applying a subspace projection (or reduced basis) method used in model order reduction studies to ``discretize'' the system's continuous spectrum. The method extracts the continuum physics from solving Schr\"odinger equations with bound-state-like boundary conditions and emulates this extraction in the space of the input parameters. This parameter emulation can readily be adapted to emulate other continuum calculations as well, e.g., those based on complex energy or Lorentz integral transform methods. Here, I give an overview of the key aspects of the formalism and some informative findings from numerical experimentation with two- and three-body systems, which indicates the non-Hermitian quantum mechanics nature of the method. A potential connection with (near-)optimal rational approximation studied in Math literature is also discussed. Further details are provided in a separate paper.