Verified Universal Breakdown of Kibble-Zurek Scaling in Fast Quenches

Abstract: The Kibble-Zurek mechanism (KZM) predicts that when a system is driven through a continuous phase transition, the density of topological defects scales universally with the quench rate. Recent theoretical work [H.-B. Zeng \textit{et al.}, \textit{Phys. Rev. Lett.} \textbf{130}, 060402 (2023)] has challenged this picture, showing that under sufficiently fast quenches, both the defect density and freezing time become independent of the quench rate and instead scale universally with the quench range. Here, we experimentally test this prediction using a single trapped-ion qubit to simulate fast quantum quenches in the Landau-Zener and 1D Rice-Mele models. We identify a critical quench rate ( v_c ) that scales with the quench range ( \delta_{\max} ), separating two distinct dynamical regimes. In the Rice-Mele model, for ( v < v_c ), the defect density follows the KZM scaling ( \sim v^{1/2} ); for ( v > v_c ), it exhibits a universal scaling ( \sim \delta_{\max} ), independent of the quench rate. Our results provide direct experimental evidence of the predicted breakdown of KZM universality under fast quenches.