The semiclassical approach to open quantum systems beyond the weak coupling regime. Quantum-classical transition and many-body interference

Dissipation of energy and the loss of quantum coherence are the main hallmarks of open quantum systems, which refers to a system coupled to many degrees of freedom of an uncontrollable environment. Due to this coupling, the system gradually loses its quantum properties and behaves more "classical". On the other hand, in the regime of large quantum numbers, semiclassical theory helps to understand quantum systems using information about their classical limit, allowing to observe interference effects between classical trajectories. This thesis aims to use the semiclassical approach to study open quantum systems. In this work, a novel notion of temperature for strongly coupled systems is developed., as well as a semiclassical treatment of decoherence in classically chaotic systems. Further, a new approach to catch interference between dissipative classical trajectories is studied, which opens the possibility to observe path interference in quantum thermodynamics.