An experiment has recorded for the first time dynamical phase transitions in the prethermal regime of a quantum system, together with a phenomenon of resonant melting of its ordered structures. The result expands the catalogue of collective behaviours that emerge in out-of-equilibrium quantum systems, a domain where classical thermodynamics no longer applies and where the usual notions of phase and temperature must be reformulated.

Dynamical phase transitions describe abrupt changes in the temporal behaviour of an isolated quantum system when a control parameter, such as the strength of a coupling or the injected energy, is varied. In the prethermal regime, the system remains for long times in a state that appears thermal but still retains information about its initial conditions, before complete thermalization erases it. Observing transitions within that time window requires controlling the dynamics with a precision not previously achieved.

The resonant melting detected appears when the excitation of the system is tuned to a characteristic frequency of its collective modes, causing the sudden collapse of the prethermal order. That behaviour recalls the melting of a solid, but driven not by temperature but by dynamical resonance. The measurement allows a phase diagram to be traced as a function of the drive and coupling parameters, clearly identifying the boundaries between the different regimes.

The work establishes an experimental framework for studying how phases organise and break down in controlled quantum systems, with implications for understanding thermalization, ergodicity and the design of quantum devices resistant to heating. Next steps include exploring whether the same transitions appear in larger systems and whether resonant melting can be used as a tool to manipulate quantum states coherently.