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.
Experiments at the Vienna Center for Quantum Science and Technology (VCQ) at the Vienna University of Technology 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 "quasi-stationary intermediate state" 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 "pre-thermalization". 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.
Ultracold Atom Clouds
"In our experiments we start with a one-dimensional quantum gas of ultracold atoms, a so-called Bose-Einstein condensate, which is then rapidly split into two using an atomchip", Professor Jrg Schmiedmayer (Vienna University of Technology) explains. When the two parts of the condensate are immediately rejoined, they create an ordered matter-wave interference pattern. "The shape of this interference pattern shows us that the two clouds have not yet forgotten that they originally came from the same atom cloud", says Jrg Schmiedmayer.
Novel State between Order and Equilibrium
After some time, the split atom cloud is expected to tend towards thermal equilibrium. As more time is allowed to pass before the two halves of the system are rejoined, the order seen in the interference pattern
|Contact: Florian Aigner|
Vienna University of Technology