# Theoretical Physics

**Theoretical Physics** is concerned with the description of natural processes. Concepts, such as analytical and numerical methods, are developed, physical phenomena is modeled and investigated, and predictions and suggestions for experiments are established.

The wide-ranging research in the theoretical physics group deals with solids and condensed matter, quantum optics, atomic and molecular physics, statistical physics and dynamic systems, and the phenomenology of elementary particles.

At the Institute for Nuclear and Particle Physics, theoretical research addresses the fundamentals of quantum field theory, as well as the physics of elementary particles beyond the Standard Model.

At the Institute for Theoretical Physics, a common interest lies in the dynamics of strongly interacting, quantum multi-particle systems and complex quantum systems under the influence of external fields. Often, systems and materials are investigated which lie on the border of classical and quantum physics.

In the area of solid state physics and condensed matter, the focus is on strong correlations, limited dimensionalities, and topological properties. Furthermore, magnetic and transport properties, superconductivity and quantum phase transitions are studied with the additional goal of discovering materials with new kinds of properties and explaining their behaviour. Polymers and complexes relevant to bioscience are also a part of the research.

Other focus areas are the investigation of quantum-mechanical and classical dynamic systems, which exhibit both regular and chaotic behaviour. In the areas of optics and atomic and molecular physics, the following topics are studied: light-matter interaction, strong fields, quantum electrodynamics, quantum information, quantum chemistry, and ultracold atomic gases and clusters.

Methods and concepts used to investigate these topics include the quantum multi-particle and quantum field theories, the Theory of Dynamic Systems, statistical physics, and stochastics. We study fundamental concepts for describing equilibrium and non-equilibrium complex (quantum) dynamic systems, and opportunities to understand their behaviour qualitatively, as well as to characterise their microscopic states.

To achieve these goals, sophisticated numerical simulations are an increasingly important part of our research.

The following professorships work in this field:

### At the Institute of Theoretical Physics:

- M. Vojta, Theoretical Solid State Physics
- W. Strunz, Theoretical Quantum Optics
- C. Timm, Theory of Condensed Matter
- R. Ketzmerick, Computational Physics
- M. Timme, Network Dynamics
- J. Budich, Quantum Many-Body Theory
- H. Tu, Correlated Electrons and Topology
- J. van den Brink, Solid State Theory (IFW)
- R. Schützhold, Theory of Nonequilibrium Phenomena in Solids or Plasmas (HZDR)
- H.-J. Sommer, Theory of Polymer Interfaces (IPF)
- J.-M. Rost, Theoretical Quantum Dynamics (MPI-PKS)
- R. Moessner, Many-Particle Physics (MPI-PKS)
- H. Kantz, Statistical Physics (MPI-PKS)
- F. Jülicher, Theoretical Biophysics (MPI-PKS)
- U. Saalmann, Theorie endlicher Vielteilchensysteme (MPI-PKS)