Rydberg atoms and cavities: measurements and manipulations of quantum fields

A particularly simple matter-radiation system is made of long-lived, circular, Rydberg atoms interacting with very high quality superconducting millimeter-wave cavities. The results of such experiments can be interpreted directly in terms of the most basic postulates of quantum mechanics and quantum measurement theory. 'Schroedinger cats' or 'quantum teleportation' put in evidence the most striking aspects of quantum mechanics. We present here briefly the theoretical framework and discuss recent experimental results 'measurement of light/ Lamb shifts in a single mode containing one/zero photon). (authors)