On the criticality of the configuration-space statistical geometry

Abstract: While phases and phase transitions are conventionally described by local order parameters in real space, we present a unified framework characterizing the phase transition through the geometry of configuration space defined by the statistics of pairwise distances $r_H$ between configurations. Focusing on the concrete example of Ising spins, we establish crucial analytical links between this geometry and fundamental real-space observables, i.e., the magnetization and two-point spin correlation functions. This link unveils the universal scaling law in the configuration space: the standard deviation of the normalized distances exhibits universal criticality as $\sqrt{\mathrm{Var}(r_H)}\sim L^{-2\beta/\nu}$, provided that the system possesses zero magnetization and satisfies $4\beta/\nu < d$. Numerical stochastic series expansion quantum Monte Carlo simulations on the transverse-field Ising model (TFIM) validate this scaling law: (i) It is perfectly validated in the one-dimensional TFIM, where all theoretical criteria are satisfied; (ii) Its robustness is confirmed in the two-dimensional TFIM, where, despite the theoretical applicability condition being at its marginal limit, our method robustly captures the effective scaling dominated by physical correlations; (iii) The method's specificity is demonstrated via a critical control experiment in the orthogonal $\hat{\sigma}^x$ basis, where no long-range order exists, correctly reverts to a non-critical background scaling. Moreover, the distribution probability $P(r_H)$ parameterized by the transverse field $h$ forms a one-dimensional manifold. Information-geometric analyses, particularly the Fisher information defined on this manifold, successfully pinpoint the TFIM phase transition, regardless of the measuring basis.