" Schrödinger cats " in cavity quantum electrodynamics : dispersive atom-field interaction

The eighth and ninth lessons were devoted to Schrödinger cats produced in cavity quantum electrodynamics experiments. An atom interacts with the field stored in a high-surge cavity, and its strongly non-linear coupling with the field produces photonic states entangled with the atom and exhibiting different components, separated by a large distance in phase space. The decoherence of these superpositions can be studied by sending a second, so-called "probe" atom into the cavity, sensitive to the coherences left in the field by the first atom. More specifically, we described the case where the atom and the field are resonant in the eighth lesson, and the case where their interaction is non-resonant (dispersive) in the ninth. In fact, the material in these last two lessons is directly related to the research work being carried out this year in the Cavity Quantum Electrodynamics team at ENS. Indeed, the subject of this year's lecture has been an inspiration for the design of new experiments, carried out in the last few months after the lecture was given (see the "research activities" section of this report).