The Lamb shift in a Kerr nonlinear blackbody (KNB) is studied in the framework of nonrelativistic quantum electrodynamics theory. It is found that the Lamb shift in a KNB depends on the absolute temperature and the Kerr nonlinear coefficient. Below a transition temperature
Tc, the Lamb shift is larger than that in a nonabsorbing linear medium. Under some conditions, the Lamb shift in a KNB can become much larger than that in a nonabsorbing linear medium or in free space. Above
Tc, the Lamb shift equals that in a nonabsorbing linear medium. The application of our theory is also discussed.
When a single excitation is shared between a large number of two-level systems, a strong enhancement of the spontaneous emission appears. This phenomenon is known as superradiance. This enhanced rate can be accompanied by a shift of the emission frequency, the cooperative Lamb shift, issued from the exchange of virtual photons between the emitters. In this work we present a semiconductor optoelectronic device allowing the observation of these two phenomena at room temperature. We demonstrate experimentally and theoretically that plasma oscillations in spatially separated quantum wells interact through real and virtual photon exchange. This gives rise to a superradiant mode displaying a large cooperative Lamb shift.