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Abstract

Eigenvector continuation (EC) has recently attracted a lot attention in
nuclear structure and reactions as a variational resummation tool for many-body
expansions. While previous applications focused on ground-state energies,
excited states can be accessed on equal footing. This work is dedicated to a
detailed understanding of the emergence of excited states from the eigenvector
continuation approach. For numerical applications the one-dimensional quartic
anharmonic oscillator is investigated, which represents a strongly
non-perturbative quantum system where the use of standard perturbation
techniques break down. We discuss how different choices for the construction of
the EC manifold affect the quality of the EC resummation and investigate in
detail the results from EC for excited states compared to results from a full
diagonalization as a function of the basis-space size.