Two‐level atom shows photon antibunching

What happens to a two‐level atom in an intense laser field? The system resembles the hydrogen atom in its relative simplicity, but only in the last couple of years have experiments shed much light on its behavior. Intensity‐dependent resonant light scattering has been studied in two‐level atoms by looking at the spectrum and more recently, by observing the time development of fluorescence—photon antibunching. Such scattering is one of the few electromagnetic phenomena that apparently cannot be described by semiclassical arguments; a quantum field theoretical approach appears essential.