SFB 1225: Isolated quantum systems and universality in extreme conditions (ISOQUANT)

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The understanding of isolated quantum systems in extreme conditions requires the resolution of outstanding open questions, which are relevant for a wide range of topical applications from particle and nuclear physics to atomic and condensed matter physics. Many such systems exhibit characteristic common properties despite dramatic differences in key parameters such as temperature, density, field strength and others. The existence of universal regimes, where even quantitative agreements between seemingly disparate physical systems can be observed, drives a remarkable convergence of research activities across traditional lines of specialisation.Our goal is the classification and quantitative understanding of universal aspects of isolated quantum systems in extreme conditions, as well as gaining insight into the question of how particular microscopic systems deviate from universality. Focussing on isolated systems offers particularly clean experimental and theoretical settings. Extreme conditions enhance the loss of memory of microscopic properties from which universality originates. More precisely, we investigate extreme conditions where the dimensionless combination of the interaction strength, field expectation values and characteristic energy scale becomes of order unity. Apart from strong couplings, this takes into account also relevant weak-coupling regimes in the presence of strong fields or large fluctuations. During the first funding period we discovered new universality classes in these regimes, providing exciting new links between different physical systems ranging from hot plasmas to cold gases.An important strength of this proposal concerns the investigation of transient phenomena as well as equilibrium properties from a common perspective. This allows us to address some of the most pressing questions concerning the thermalisation process, the interplay of strong fields with the vacuum and matter, and the phase structure of systems in extreme conditions. Experimentally, these questions will be investigated with the help of ultrarelativistic heavy-ion collisions, precision spectroscopy with highly charged ions, and ultracold quantum gases. While the former explore the theory of the strong interaction (QCD) and quantum electrodynamics (QED), ultracold quantum gases are used to engineer generic model systems as quantum simulators for complex many-body problems. The scope of this research programme requires a concerted effort across different fields of specialisation for which Heidelberg provides an ideal environment.