Cooperative Phenomena

Jonathan D. Pritchard

Nicolai G. Basov

V. Buonomano

V. P. Karassiov

1. Cooperative phenomena and processes in various many-body physical systems (atoms, molecules, nuclei etc.) are now the topic of great interest (see e.g. [ 1-6 ] and references therein). A natural and efficient tool for studying cooperative phenomena in quantum systems is the second quantization method [ 7 ], which is closely connected with the representation theory of Lie groups and supergroups [ 8 – 12 ]. Therefore, group-theoretical methods are very adequate to an analysis of different cooperative effects within the general approach of dynamic symmetries [ 13 ].

F. T. Arecchi, E. Courtens

Phenomena of coherent resonant propagation can be considered as resulting from the cooperative interaction of a certain number of excited two-level systems. It is shown that these phenomena can be characterized by a specific "maximum cooperation number" and by the associated "cooperation time." These are defined for the superradiant state, but their meaning and usefulness can be extended to other situations. The alternative description of of superradiance as a spontaneous or as a stimulated effect is also discussed and it is shown that with the help of the new concepts, the Dicke quantum perturbative treatment can be reconciled with the semiclassical theories.

D. J. Wallace

Some of the most interesting physical phenomena arise from the cooperative behaviour of many particles. By their very nature these cooperative phenomena can be extremely difficult to describe theoretically. In this article Dr D J Wallace explains how the renormalization group provides a technique for tackling such problems