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We investigate the physical properties of complex quantum systems, such as e.g. Brownian systems, mesoscopic superconducting systems, nanowires and macromolecules. One main focus is on QUANTUM DISSIPATION i.e., on the influence of the environment on the dynamical or equilibrium properties of small quantum systems. On the one hand the entanglement of the small system with the degrees of freedom of the environment yields a loss of quantum coherence of the small quantum system. We aim at understanding the origin of damping and its optimization in real devices. We focus e.g. on dissipative bistable systems and decoherence in solid state nanocircuits used for quantum computation. On the other hand, we also study model systems, as e.g. Brownian motors, where noise does not constitute a nuisance. In contrast, it can be used to drive particles along pre-assigned directions.

The other main focus is on QUANTUM TRANSPORT in low dimensional systems, as e.g. quantum dots, macromolecules or quantum wires. One one side we focus on the effects of the Coulomb interaction among electrons in low-dimensionality systems, e.g. small metallic systems weakly coupled to leads (quantum dots), or one-dimensional systems e.g. carbon nanotubes. On the other hand we investigate novel forms for transfer of information, e.g, upon using the spin rather than the charge degree of freedom of an electron, or upon using nano-molecules as building blocks of electronic devices.

We perform analytical and numerical calculations based on the path-integral formalism, Green's functions techniques and the Bloch-Redfield approach.