Nonlinear Quantum Optics With Few Atoms

Under appropriate conditions already a single atom is sufficient to induce nonlinear optical effects like laser or maser action or optical Instability. In this extreme microscopic limit of individual atoms and small photon numbers, signatures of nonclassical effects must be visible. Manifestations of quantum behavior are observed either in the statistical properties of the emitted light or in the population statistics of the atomic beam which passes through the interaction zone. While the tools for a quantitative description of the field statistics are well developed, the level specific counting probabilities for atomic beams have not been described in a quantitative way yet.