A thermodynamic route to the quantum-to-classical transition

Microscopic systems (such as electrons, atoms, or faint light fields) can be prepared, according to the principles of quantum mechanics, in physical configurations with no classical counterpart. Such a possibility appears to be precluded when the degree of ‘complexity’ of the system at hand (intended as its size, mass or the number of its elementary constituents) grows towards the macroscopic domain. Indeed, our daily observations do not readily give us any evidence of non-classical behaviour of the macroscopic world around us. Is there any reason preventing the establishment of quantum features at the macroscopic scale? And how is quantumness lost as we abandon the microscopic domain? These questions address the phenomenon known as quantum-to-classical transition, i.e. the process through which quantum features are lost in favour of a fully classical description of a physical system. The characterization of the QtC transition is one of the most interesting and challenging goals of modern research in quantum mechanics. In this Colloquium I will discuss how fundamental progress can be made towards a better grasp of the quantum-to-classical crossover by adopting a novel methodological approach based on the non-equilibrium thermodynamics of quantum evolutions. Harnessing the fundamental interplay between complexity and quantumness will underpin the development of more resilient architectures for quantum information processing.