Electric Flux as a Criterion for String Breaking and Schwinger Pair Production

Abstract

We define string breaking by the midpoint electric field falling to half a flux unit. In the massive Schwinger model, an energy balance between intact string and screened configuration predicts this separation using only vacuum observables and meson masses as input. We observe numerically that this half flux point corresponds to equal weights of the two configurations thus explaining the observed peak of the entanglement entropy as maximal uncertainty of the binary flux. The same binary uncertainty explains the entanglement peak at the vacuum transition. Near breaking, screening organizes part of the spatial entanglement between the string interior and exterior into a nearly maximally entangled bit. Within the selected flux sectors, this approximate encoded Bell pair records whether the flux is screened and nearly separates from the remaining correlations. The vacuum transition exhibits the same structure. The string and the $θ$-vacuum reveal a matching structure of the capacity of entanglement minimum at their transition point, linking their entanglement spectra. The transition rearranges degrees of freedom coherently as revealed by the entanglement asymmetry and Robustness of Magic of disjoint subregions. Finally, we construct the $θ$-vacuum and string wavefunctions with high fidelity using a restricted Boltzmann machine ansatz.