Understanding more with less

Thermodynamics is commonly believed to be an effective long scale theory for macroscopic, complex systems. However, this work sets off to search for thermodynamic behavior in simple small model systems. Part I addresses such fundamental non-equilibrium processes as decoherence and energy transport microscopically. In particular, superfluid internal con-vection is identified as the genuine effect of heat transport in weakly interacting Bose-condensed gases. In Part II, a microscopic engine model is developed and investigated both classically and quantum mechanically. Even though too small to be described in terms of ordinary thermodynamics, a general efficiency limit is found. Based on this fundamental insights, a possible extension of the principles of thermodynamics into the microscopic regime is discussed.