Conformal Data for the $O(2)$ Wilson-Fisher CFT in $(2+1)$-Dimensional Spacetime from Exact Diagonalization and Matrix Product States on the Fuzzy Sphere

TL;DR

This paper employs exact diagonalization and matrix product states on the fuzzy sphere to numerically extract conformal data of the $O(2)$ Wilson-Fisher CFT in (2+1)D, confirming theoretical predictions.

Contribution

It introduces a fuzzy-sphere regularization preserving full rotational symmetry, enabling direct mapping of energy eigenstates to CFT operators and extracting conformal data.

Findings

Identified 32 primary operators and their descendants.

Good agreement of scaling dimensions with conformal bootstrap.

Verified large charge expansion predictions connecting Goldstone modes to phonons.

Abstract

We study at zero temperature a microscopic quantum spin-1 model on the fuzzy sphere that realizes the $O(2)$ Wilson-Fisher conformal field theory (CFT) in $(2+1)$-dimensional spacetime at a quantum critical point. Here, we use the fuzzy-sphere regularization as it preserves the full spatial $SO(3)$ rotational symmetry of the CFT, enabling the state-operator correspondence that maps energy eigenstates directly to CFT operators. Using exact diagonalization (ED) and matrix product state (MPS) techniques combined with conformal perturbation theory (CPT), we extract conformal data including scaling dimensions and operator product expansion (OPE) coefficients. We identify 32 primary operators and their descendants, organized by the conserved $O(2)$ charge $S^{z}$ and spatial angular momentum $L$. Our numerical results for the scaling dimensions of the lowest primary operators show good agreement with conformal bootstrap predictions. We verify predictions from the large charge expansion, which provides systematic predictions for operators carrying large $U(1)$ charge, connecting the Goldstone mode physics in the ordered phase to phonon primaries at the critical point.