The thermodynamic of negative absolute temperatures

Abstract

In the last two decades, the advent of quantum technologies and the improvement of means for assessing biological engines have fuelled the interest in understanding the physics of out-of-equilibrium small scale systems. Indeed, while is indisputable that thermodynamics is a cornerstone of any description of physical processes occurring in macroscopic systems, the perspective of having nano-mesoscopic systems operating on demand pushes one to deal with conditions for which thermodynamics loses accuracy. Even more, as the system gets smaller, quantum effects become relevant, introducing a new physical origin for fluctuations observed in their processes. In this context, it is a fair question whether the laws of thermodynamics are still valid, which naturally has fomented very much interest in the field. By the application of fluctuation theorems and stochastic thermodynamics, important progresses have been made in this arena, not only providing significant connections between thermodynamics and quantum information as well as leading to what is known as quantum fluctuation theorems. Indeed, soon it became clear that even the most basic physical concepts, e.g., work and cyclic processes, should be revisited. This project seeks to study the thermodynamics of systems showing bounded energy spectrum, with special attention to the controversy about the existence of negative absolute temperatures and their implications for the thermodynamic quantities as efficiency.