Isolated quantum systems in extreme conditions

Over the past years, quantum systems in extreme conditions have become a unifying research theme crossing traditional lines of specialisation from high-energy and nuclear physics to atomic and condensed matter physics. Quantum systems in extreme conditions can exhibit characteristic common properties despite dramatic differences in key parameters such as temperature, density or field strength. The existence of universal regimes, where even quantitative agreements between seemingly disparate physical systems can be observed, drives a remarkable convergence of research activities. This allows us to ask closely related questions and often even the same ones for very distinct physical platforms. Together, the synergies help us to give more complete answers to outstanding questions than individual systems could provide. Much progress is achieved in this way, opening-up new perspectives on long-standing problems. Our focus in the Collaborative Research Centre 1225 concerns research on extreme conditions experimentally realised in ultracold quantum gases as versatile model systems for complex few- to many-body problems. This allows us to address some of the most pressing questions about the thermalisation process, ie. how a closed quantum system can relax and how a stable classical world can emerge from ever fluctuating quantum systems as well as entering the regime of out-of- equilibrium physics. Outstanding problems, such as the origin of collectivity in few-body systems or new forms of hydrodynamic descriptions far from equilibrium, become accessible in this way. The questions on the emergence of effective theories are seen to be closely linked to information theoretic concepts, which will be further explored. While initially the different physical systems were mainly linked by common theoretical concepts and universal phenomena, this proposal for the third funding period increasingly implements also direct collaborations between experimentalists of the very distinct participating platforms bridging from giant collider facilities to compact table-top setups! A new generation of internationally successful scientists with strong links across the different fields of specialisation is establishing, and ISOQUANT has evolved into a significant platform for nurturing the careers of early professionals, shaping one of the central international research themes in quantum physics.