Mesoscopic systems

Mesoscopic physics explores the ramifications of quantum mechanics in the physics of systems of near classical proportions. Examples of mesoscopic systems include metallic or semiconducting electronic devices of extension O(1\mu m) – the length scales characteristic for highly integrated
electronic circuits – cold atomic condensates, optomechanical devices, and more. Thanks to recent advances in nanotechnology and experimentation, quantum phenomena hitherto limited to the subatomic world are now becoming accessible in systems thus large, and this opens whole new perspectives to nano-electronics and device technology. At the same time, mesoscopic physics
is a field of great conceptual depth, with ramifications in mathematical physics, quantum theory, field theory, and particle physics. Research directions currently represented at the Cologne institute for theoretical physics include the mathematical physics of mesoscopic systems, quantum nonlinear dynamics, mesoscopic nonequilibrium physics, and more.
Groups: Altland | Zirnbauer

Correlated systems

Quantum many-body systems can give rise to remarkable collective states of matter that have no counterpart in their classical analogs – archetypal examples include superfluids, superconductors, Mott insulators, and topological quantum liquids. These unusual phenomena often arise in strongly correlated systems in which the collective behavior of the elementary degrees of freedom (electrons or atoms) cannot be effectively described in terms of non-interacting entities. Our groups study strong correlations in electronic materials, typically transition metal oxides, which exhibit a complex interplay of spin, charge and orbital degrees of freedom, as well as systems of trapped ultracold atoms – often in close collaboration with experimental groups (e.g. within SFB 608).
Groups: Rosch | Trebst

Computational Physics

Connecting the emergent collective behavior of interacting many-body systems to a microscopic understanding is often rendered extremely difficult due to the presence of strong correlations and/or multiple energy scales. Our groups develop and apply a variety of sophisticated numerical approaches that exploit concepts from statistical physics, quantum information theory, and computer science to overcome these problems thereby gaining conceptual insight as well as quantitative understanding. Systems of current interest are materials which exhibit the rich phenomena induced by frustration arising from competing interactions, systems at and in proximity of (quantum) phase transitions as well as quantum systems out of equilibrium.
Groups: Bulla | Trebst

Gravitation and relativity

Among the known interactions in Nature, gravitation is unique in that it acts universally on all kinds of matter and energy. It dominates on large scales (cosmology) and for compact objects (neutron stars, black holes), but is also important for everyday physics. The gravitational interaction plays a central role in the interplay between astrophysics, cosmology, and particle physics.
Our group investigates Einstein's theory and its possible extensions in both the classical and the quantum regime. The methods involved include quantisation of general relativity, an analysis of its gauge structure, and quantum theory in curved backgrounds. Particular applications are cosmology and the physics of black holes.
Group: Kiefer