The Quantum World Only Partially Melts
Every day we observe systems thermalizing: Ice cubes in a pot of hot water will melt and will never remain stable. The molecules of the ice and the molecules of the water will reach thermal equilibrium, ending up at the same temperature. Well-ordered ice crystals turn into a disordered liquid.
Recent experiments have shown that in the quantum world the transition to thermal equilibrium is more interesting and more complicated than assumed so far. Between an ordered initial state and a statistically mixed final state, a so-called â€œquasi-stationary intermediate stateâ€ can emerge. This intermediate state already exhibits some equilibrium like properties, but some of the distinct order of the initial state remains visible for a remarkably long time. This phenomenon is called â€œpre-thermalizationâ€. Pre-thermalization is predicted to play a major role in many different non-equilibrium processes in quantum physics. It could, for example, help us to understand the state of the early universe.