Thermodynamics studies energy conversion processes across nature and technology, from large to small scales. Since matter and energy are described by quantum physics at extremely small scales, there came the necessity to understand how thermodynamics, a classical theory of physics applicable at large scales, fits together with quantum physics. Thus, the field called "quantum thermodynamics" aims to understand the principles of energy conversion in the quantum regime. In particular, the field is concerned with investigating (i) how thermodynamic quantities, like heat and work, can be defined for quantum systems; (ii) the role of quantum effects, finite-size effects and fluctuations in thermodynamic quantities; (iii) how to build efficient quantum thermal machines and devices. The field of quantum thermodynamics has developed rapidly in the last two decades, becoming highly relevant both for the foundations of physics and for the development of efficient and sustainable quantum technologies.
Quantum systems are especially sensitive to their surroundings, where the latter exchange energy and information with the quantum system of interest. One of the main achievements of quantum thermodynamics has been the formulation of laws of thermodynamics for quantum systems interacting with classical surroundings. In these cases, the surroundings can be treated either as an ideal source of heat or work for the quantum system. However, the question of how to formulate the laws of thermodynamics for quantum surroundings remains elusive. Rapid advancements in quantum technologies, which enable the study of quantum systems interacting with quantum surroundings, demands an urgent answer. The project "Scattering approach to thermodynamics of quantum systems" (SAT-Q) has the goal of meeting this need. In SAT-Q, the surroundings are treated quantum-mechanically, consisting of particles which travel in space and collide with a quantum system of interest. By relying on scattering, a process ubiquitous in nature and experiment, SAT-Q aims at providing a fully-quantum framework for thermodynamics which can be connected with modern quantum experiments and technologies.
The first objective of SAT-Q to understand if the nature of the quantum particles, i.e. bosons or fermions, play a role in a thermodynamics of the collision event. In particular, the objective is to identify the conditions for fermions and bosons to act as heat or work sources for the quantum system. The second objective is establish a clear connection between the scattering approach and another state-of-the-art approach to quantum thermodynamics called "quantum resource theories". Resource theories, although mathematically powerful, are very abstract; establishing a connection between them and scattering theory would validate both of them and bring the former closer to experimental realization. Finally, the third objective (which is transversal to the previous objectives) is to show that the scattering approach can correctly describe energy fluctuations. Since very small and quantum systems are sensitive to external perturbations, their energy fluctuates due to interactions with surroundings; it is extremely important to verify that fluctuations in thermodynamic quantities can be captured by the scattering approach.
By completing these objectives, SAT-Q is expected to significantly advance the field of quantum thermodynamics, providing a fully-quantum framework to investigate thermodynamics which can be tested and implemented with current technology.
