Title: Quantum energetics: fundamentals and applications to simple quantum optics experiments

Quantum energetics explores the flows of energy, entropy and information in situations of quantum physics where temperature is not necessarily defined. This is the case, e.g. in measurement-powered engines, in driven-dissipative systems. In this talk, I will focus on the canonical case of two coupled systems, otherwise isolated. This captures most situations of quantum optics, where a qubit is coupled to a light field injected in one or several electromagnetic modes. Global energy conservation allows to characterize the nature of energy exchanges, yielding work-like and heat-like quantities. I apply this framework to study the energy cost of work extraction and the role of quantum coherence in quantum batteries, and present recent experimental results obtained with superconducting and semiconducting devices. I finally show how energetic quantities can help probing the quantum nature of a light field.