Universal Structure of Nonlocal Operators for Deterministic Navigation and Geometric Locking

Abstract: We establish a universal geometric framework that transforms the search for optimal nonlocal operators from a combinatorial black box into a deterministic predict-verify operation. We discover that the principal eigenvalue governing nonlocality is rigorously dictated by a low-dimensional manifold parameterized by merely two fundamental angular variables, $θ$ and $φ$, whose symmetry leads to further simplification. This geometric distillation establishes a precise mapping connecting external control parameters directly to optimal measurement configurations. Crucially, a comparative analysis of the geometric angles against the principal eigenvalue spectrum, including its magnitude, susceptibility, and nonlocal gap, reveals a fundamental dichotomy in quantum criticality. While transitions involving symmetry sector rotation manifest as geometric criticality with drastic operator reorientation, transitions dominated by strong anisotropy exhibit geometric locking, where the optimal basis remains robust despite clear signatures of phase transitions in the spectral indicators. This distinction offers a novel structural classification of quantum phase transitions and provides a precision navigation chart for Bell experiments.