Non-ergodic dynamics in SU(2) lattice gauge theory: scars, fragmentation, and disorder-free localization

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Non-Abelian lattice gauge theories provide a setting where local constraints reshape far-from-equilibrium quantum many-body dynamics and can obstruct thermalization. In a (1+1)D SU(2) lattice gauge theory with dynamical matter, three non-ergodic phenomena are identified, each with a different origin. In regimes where the gauge-invariant dynamics is otherwise ergodic, low-overhead product-state quenches exhibit robust quantum many-body scarring, seen as long-lived coherent oscillations in local observables and pronounced fidelity revivals enabled by non-Abelian meson and baryon–antibaryon excitations. In a separate region of parameters, the gauge-invariant model becomes nonthermal yet delocalized due to Hilbert-space fragmentation into disconnected Krylov subsectors. Finally, when static SU(2) background charges are introduced to encode gauge superselection sectors, and the system is initialized in a coherent superposition of these sectors, disorder-free localization emerges even where a fixed sector is ergodic: spatial matter inhomogeneities persist at long times, and entanglement exhibits MBL-like (logarithmic) growth. These results provide a unified benchmark suite for non-ergodic far-from-equilibrium dynamics in non-Abelian constrained systems and are compatible with digital quantum simulation on existing qudit platforms.

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