  The study of open quantum systems (OQSs), i.e., systems interacting with an
environment, impacts our understanding of exotic nuclei in low-energy nuclear
physics, hadrons, cold-atom systems, or even noisy intermediate-scale quantum
computers. Such systems often exhibit resonance states characterized by energy
positions and dispersions (or decay widths), the properties of which can be
difficult to predict theoretically due to their coupling to the continuum of
scattering states. Dealing with this phenomenon poses challenges both
conceptually and numerically. For that reason, we investigate how the reduced
basis method known as eigenvector continuation (EC), which has emerged as a
powerful tool to emulate bound and scattering states in closed quantum systems,
can be used to study resonance properties. In particular, we present a
generalization of EC that we call conjugate-augmented eigenvector continuation,
which is based on the complex-scaling method and designed to predict
Gamow-Siegert states, and thus resonant properties of OQSs, using only
bound-state wave functions as input.
