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 p articular, cooperativity is analyzed in relation to NDD processes in multic omponent systems that generate intrinsic superradiant-like behavior, as wel l as intrinsic optical bistability (IOB). Interpretation and comparison wit h the historical cooperativity parameterization stemming from supefluoresce nce (SF) and absorptive optical bistability (AOB) manifests the similaritie s, but also the essential differences, arising from local versus nonlocal e ffects and intrinsic versus extrinsic effects. The fundamental basis for th ese distinctions is discussed. These concepts are linked to single atom coo perativity in cavity quantum electrodynamics (QED). Published by Elsevier S cience B.V.