Cooperativities in two-level systems

Cooperativity, the competition between macroscopic cooperative behavior and single atom behavior, is discussed in relation to near-dipole-dipole (NDD) interactions that depend upon a single cooperativity parameter C-NDD. In particular, cooperativity is analyzed in relation to NDD processes in multicomponent systems that generate intrinsic superradiant-like behavior, as well as intrinsic optical bistability (IOB). Interpretation and comparison with the historical cooperativity parameterization stemming from supefluorescence (SF) and absorptive optical bistability (AOB) manifests the similarities, but also the essential differences, arising from local versus nonlocal effects and intrinsic versus extrinsic effects. The fundamental basis for these distinctions is discussed. These concepts are linked to single atom cooperativity in cavity quantum electrodynamics (QED). Published by Elsevier Science B.V.