Open quantum systems

Real quantum systems are never completely isolated. Often they are embedded in reservoirs with many degrees of freedom such as electromagnetic modes of a circuit or the vacuum of a cavity, phonons, or solvent modes. Understanding open quantum systems is one of the central issues of current activities in quantum physics and quantum device technology.

Our group has developed techniques to capture equilibrium and dynamical properties of these systems beyond conventional weak-coupling (e.g. master equations). This includes very strong dissipation in the quantum Smoluchowski regime, path integral Monte Carlo simulations for spin systems, and the stochastic Liouville-von Neumann approach. The latter is particularly suited to explore intricate correlations between driving and dissipation also using optimal control. Apart from conceptual questions, we address together with experimentalists e.g. the control of quantum bits and phase transitions in spin-boson models.