Thermal machines in the quantum world

Thermodynamics, developed in its basic structure in the 19th century, is based on a coarse-grained viewpoint, abstracting from details, to give a description of a plethora of physical systems. This way she advanced to the bases for many key technologies that made our modern society possible. The heat engine converts heat (disordered energy) into mechanical energy (work). Examples are the steam engine, steam turbine and all internal combustion engines. A power heat engine transports thermal energy from a lower temperature level to a higher one using mechanical energy. Examples are a heat pump or a refrigerator. However, quite new questions - going beyond the traditional picture of thermodynamics - arise when looking for a description of small systems for which stochastic fluctuations are relevant, or even of machines for which quantum effects play a central role. In recent years, the potential and limitations of the resulting quantum thermodynamics and the resulting thermodynamic transformations for entanglement, quantum fluctuations, quantum information exchange, and coherences have begun to be explored. Despite some important progress, many conceptual issues are still unclear. Perhaps even more urgently, there are no experimental realizations that convincingly demonstrate the potential of the intended advantage of quantum effects. This planned Research Unit faces up to these challenges. It brings together leading researchers in quantum thermodynamics in experiments - on trapped ions, ultracold atoms or NV centers - and theory to explore new approaches. On one hand, quite significant developments of experimental platforms are needed to actually detect and exploit true quantum effects in work and power extraction. On the other hand, many conceptual questions are still wide open: in what sense can realistic quantum machines be more powerful than classical machines? How do small (quantum) systems thermalize? Can the traditional separation of system and bath always be carried out? What is the role of quantum correlations and entanglement? Is quantum error correction understandable within this framework? The proposed research not only promises profound insights into the fundamentals of thermodynamic processes, in a world ultimately determined by quantum processes, but also technological implications, such as new cooling techniques, quantum heat engines and quantum refrigerators. Ultimately, this Research Unit promises a breakthrough on the question of whether quantum thermodynamics has the potential to improve quantum machines and provides a framework for discussion and exchange.