  The problem of the two-photon coherent generation of entanglement photon
pairs in Quantum Optics has been intensively studied for the last years. It is
important to note that the two-quantum cooperative effects play a main role in
other fields of physics as well. The collective processes in Condensed Matter
have many analogical proprieties with cooperative radiation effects in Quantum
Optics. Recently the two-quantum generation of entanglement photons and its
applications in information technology and communication has been intensively
studied. The new cooperative emission phenomenon for dipole-forbidden
transitions of inverted system of radiators can be observed in the processes of
the two-photon spontaneous emission.

Statistical Mechanics;Superconductivity