Does an Isolated Quantum System Relax? Probing the Emergence of the Classical World by Prof Jörg Schmeidmayer

Join us at this talk by Prof Jörg Schmiedmayer from University of Technology Vienna. This talk is organised as part of the IAS Frontiers Seminars: Quantum Horizons, jointly supported by the Institute of Advanced Studies (IAS) and School of Physical and Mathematical Sciences (SPMS).

About the talk

The evolution of an isolated quantum system is unitary.  This is simple to probe for small systems consisting of few non-interacting particles.  But what happens if the system becomes large and its constituents interact? In general, one will not be able to follow the evolution of the complex many body eigenstates.

Ultra-cold quantum gases are an ideal system to probe these aspects of many body quantum physics and the related quantum fields. Our pet systems are one-dimensional Bose-gases. Interfering two systems allows studying coherence between the two quantum fields and the full distribution functions and correlation functions give detailed insight into the many body states and their non-equilibrium evolution. 

In our experiments, we study how the coherence created between the two isolated one-dimensional quantum gases by coherent splitting slowly degrades by coupling to the many internal degrees of freedom available. We find that a one-dimensional quantum system relaxes to a pre-thermalised quasi steady state which emerges through a light cone like spreading of ’de-coherence’. The pre-thermalised state is described by a generalized Gibbs ensemble. Finally, we investigate the further evolution away from the pre-thermalized state. On one side, we show that by engineering the quasi particles we can observe many body quantum revivals. On the other, we point to mechanisms that lead towards a final state that appears indistinguishable from a thermally relaxed state:  two classically separated objects.  This illustrates how classical physics can emerge from unitary evolution of a complex enough quantum system. 

About the speaker

Prof Jörg Schmiedmayer is a leading experimental quantum physicist and Professor of Physics at TU Wien, heading the Atom and Quantum Optics Group at the Atominstitut and co-leading the Vienna Center for Quantum Science and Technology (VCQ). He pioneered atom-chip technology and matter-wave interferometry, advancing research in ultracold atoms, Bose–Einstein condensates, and non-equilibrium quantum systems. His work has earned him multiple ERC Advanced Grants, the Wittgenstein Prize, and international recognition for contributions to quantum simulation, quantum optics, and many-body physics.