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## Organisation

# Theory of quantum systems and complex systems

### Research Group

Main organisation:Department of Physics

Lifecycle:1 Oct 2003 → Today

Organisation profile:The research group has developed a long standing expertise in the theory of condensed matter more specifically in the discipline of the quantum theory of the solid state. The specialties of TFVS comprise i.a. electron-phonon interaction, polaron theory, theory of super-conductivity, Kondo-systems, many particle quantum theory, Bose-Einstein condensation and fermionic superfluidity. Functional integration is the most suited method to study those systems, and TFVS has contributed to the refinement of this method. Electron-phonon interactions The research group TFVS has expertise in the quantum theory of polarons, bipolarons and the many-polaron gas. Among the milestones in polaron theory achieved in TFVS are the study of the response of polarons and the study of bipolarons with path-integral methods (both with and without magnetic field). Currently, research is focused on cyclotron resonance in low-dimensional systems, magneto-absorption of bi-polarons, many-polaron effects in high-Tc superconductors, exciton-phonon interactions, and optical properties of semiconductor quantum dots. Mesoscopic and nanoscopic superconducting structures The superconducting properties (e.g. phase boundaries) of sub-micron structures of various shapes are studied with different methods such as the Ginzburg-Landau formalism. Loops, double loops, wedges, bridges, triangles, nanograins, star-shaped superconducting samples have been analyzed, and stable vortex-antivortex patterns were predicted. Bose-Einstein condensation and fermionic superfluidity Since the observation of Bose-Einstein condensation in dilute atomic gases in 1995, the research group has actively contributed to the development of the theory for systems of trapped ultracold atoms. The expertise in path-integral methods and other many-body techniques is applied to novel experiments. Currently the focus is on matter wave fringe patterns, path-integral descriptions of resonant superfluidity, boson-fermion mixtures, and fermionic superfluidity. Various other recent topics include - Kondo systems in mesoscopic structures and Fe-Au thin film alloys - Optical properties of stacked quantum dots - Many-body path-integral methods and many-body diffusion Monte-Carlo algorithms - Quantum transport in sub-micron mosfets

Keywords:ELECTRON PHONON INTERACTION, DIELECTRIC RESPONSE, BOSE-EINSTEIN CONDENSATION, MANY BODY THEORY, PATH INTEGRALS

Disciplines:Applied mathematics in specific fields, Astronomy and space sciences, Classical physics, Condensed matter physics and nanophysics, Materials physics, Mathematical physics, Quantum physics