Collective nature of light emission by atomic ensembles yields fascinating effects such as superradiance and radiation trapping even at the single-photon level. Photon emission is influenced by virtual transitions which lead to collective Lamb shift. For large samples light emission is also affected by retardation due to the finite value of the speed of light. I will discuss collective emission of a single photon from a cloud of N atoms and show exact analytical solutions of this many-atom quantum mechanical problem for superradiant and trapped states. I will discuss how virtual and nonlocal effects modify evolution of the atomic system yielding peculiar temporal features and new kind of cavity QED. I will also show that fully quantum mechanical treatment of spontaneous emission of weakly excited atomic ensembles is analogous to emission of N classical harmonic oscillators.

Location: Physics Bldg., Room 401