Physics-informed quantum algorithms for glueball-like excitations in a $\mathbb{Z}_2$ lattice gauge theory

Abstract

Glueball spectroscopy with quantum computing requires both a correlated gauge vacuum and a systematic construction of its low-lying pure-gauge excitations. We develop a physics-informed quantum-computing framework for these tasks in a $(2+1)$-dimensional $\mathbb{Z}_2$ lattice gauge theory. We use the term \emph{glueball-like} for localized closed-flux excitations on the confining side of this Abelian model, without identifying them with the non-Abelian glueballs of QCD. The central strategy is to organize the computation around the physical structure of the glueball-like state rather than to search a generic many-body excitation space. We prepare the gauge vacuum variationally and use Wilson-loop quantum subspace expansion to construct and characterize the low-lying excitations. Moreover, eigenvector continuation uses nearby ground states to capture the growing loop dressing without a rapidly enlarged Wilson-loop basis, while a Bethe--Salpeter-type radius quantifies the associated spatial broadening. We further use quench dynamics to probe nonequilibrium production. Although demonstrated in an Abelian model, the framework is built from gauge-invariant vacuum and excitation structures and is naturally transferable to non-Abelian lattice gauge theories.