Inverse problems for selfadjoint Schr\"odinger operators on the half line with compactly-supported potentials

TL;DR

This paper investigates the uniqueness of reconstructing a compactly-supported potential and boundary parameter for a Schrödinger operator on the half line from scattering data, introducing concepts like eligible resonances and providing reconstruction methods.

Contribution

It establishes conditions for unique determination of potential and boundary parameter from scattering data, introduces eligible resonances, and outlines reconstruction procedures.

Findings

Uniqueness of potential and boundary parameter from scattering matrix, except in a special case.

Characterization and role of eligible resonances in potential reconstruction.

Explicit reconstruction methods for potentials from scattering data and Jost function.

Abstract

For a selfadjoint Schr\"odinger operator on the half line with a real-valued, integrable, and compactly-supported potential, it is investigated whether the boundary parameter at the origin and the potential can uniquely be determined by the scattering matrix or by the absolute value of the Jost function known at positive energies, without having the bound-state information. It is proved that, except in one special case where the scattering matrix has no bound states and its value is $+1$ at zero energy, the determination by the scattering matrix is unique. In the special case, it is shown that there are exactly two distinct sets consisting of a potential and a boundary parameter yielding the same scattering matrix, and a characterization of the nonuniqueness is provided. A reconstruction from the scattering matrix is outlined yielding all the corresponding potentials and boundary parameters. The concept of "eligible resonances" is introduced, and such resonances correspond to real-energy resonances that can be converted into bound states via a Darboux transformation without changing the compact support of the potential. It is proved that the determination of the boundary parameter and the potential by the absolute value of the Jost function is unique up to the inclusion of eligible resonances. Several equivalent characterizations are provided to determine whether a resonance is eligible or ineligible. A reconstruction from the absolute value of the Jost function is given, yielding all the corresponding potentials and boundary parameters. The results obtained are illustrated with various explicit examples.