The problem of collective spontaneous emission has recently received growing interest with the study of single photon superradiance from N two-level atoms prepared by the absorption of one photon. Considering the decay of atoms prepared in the "timed Dicke state", strong forward emission is expected for extended systems, with a cooperative decay rate proportional to N and inversely proportional to the square of the atomic cloud size.
I will discuss our recent results on cooperative scattering by a cloud of cold atoms and will present the experiments which lead to the first observation of these effects. I will then briefly explain how subradiant states, where the energy remains partially trapped in the atomic system, can be observed and controlled in large cloud of cold atoms.
Finally, I will mention an original technique for compressing an atomic cloud which would allow us to study the interplay between disorder and cooperativity in the dense regime of light-mater interaction (distance between two atoms wavelength).