Observation of prethermal dynamical phase transitions and resonant melting

The dynamics of isolated quantum systems following a sudden quench has a central role in many areas of material science, high-energy physics and quantum chemistry^1-4. Such far-from-equilibrium quantum dynamics-which features complex phenomena with implications for thermalization, non-equilibrium phase transitions and Floquet phase engineering^5-8-is challenging to study numerically, in particular, in high-dimensional systems^9,10. Here we use a programmable neutral-atom quantum simulator¹¹ to systematically explore quench dynamics in spin models with up to 180 qubits. By initializing the system in a product state and performing quenches across a broad parameter space, we discover several stable, qualitatively distinct dynamical regimes. We trace their robustness to Floquet-like prethermal steady states⁸ that are stabilized over exponentially long emergent timescales by strong dynamical constraints. We further observe sharp peaks in the dynamical response that are quantitatively explained by the structured melting of prethermalization through resonances. In two dimensions, we uncover a prethermally driven, first-order dynamical phase transition linked to the proliferation of Néel-order defects^6,12, and probe it quantitatively using a generalized Clausius-Clapeyron test. Together, these results establish a programmable route to high-energy prethermal phase structure: long-lived dynamical phases, their resonant breakdown and a first-order dynamical phase transition that is not inherited from the equilibrium phase boundaries.