Temperature of the two-level system in a strong radiation field

The two-level system interacting with a strong resonance field is theoretically investigated. Two cases of temperature existing (a) on the energy levels in the Schroedinger representation (Tsub(s)) and (b) on the quasi-stationary energy levels, defined by the quantized field amplitude, (Tsub(QE)), are considered. The possibility of temperature establishment Tsub(QE) is investigated. The polarization of the system with temperature Tsub(QE), induced by a weak probe field, is calculated. This polarization is proved to be different from that of the system with temperature Tsub(s). In the latter case the effect of the probe field is similar to the parametric resonance, whereas in the former case it is determined by resonance transitions between quasi-stationary energy levels. (Auth.)