After a PhD dissertation on dressed atoms under the supervision of Claude Cohen-Tannoudji (himself a Nobel Prize recipient) from 1967 to 1971, he developed new methods for laser spectroscopy, based on the study of quantum beats and superradiance. He then moved on to Rydberg atoms, giant atomic states particularly sensitive to microwaves, which makes them well adapted for studying the interactions between light and matter. He showed that such atoms, coupled to a superconducting cavity containing a few photons, are well-suited to the testing of quantum decoherence and to the realization of quantum logic operations necessary for the treatment of quantum information.