Super-radiance and the unstable photon oscillator

If the damping of a simple harmonic oscillator from a thermally random forc e is sufficiently strong, then the oscillator may become unstable. For a ph oton oscillator (radiatively damped by electric dipole moments), the instab ility leads to a low temperature Hepp Lieb-Preparata super-radiant phase tr ansition. The stable oscillator regime is described by the free energy of t he conventional Casimir effect. The unstable (strongly damped) oscillator h as a free energy corresponding to Dicke super-radiance.