  We extend the analysis of the effects of electromagnetic (EM) fields on
mesoscopic conductors to include the effects of field quantization, motivated
by recent experiments on circuit QED. We show that in general there is a
photovoltaic (PV) current induced by quantized cavity modes at zero bias across
the conductor. This current depends on the average photon occupation number and
vanishes identically when it is equal to the average number of thermal
electron-hole pairs. We analyze in detail the case of a chaotic quantum dot at
temperature T_e in contact with a thermal EM field at temperature T_f,
calculating the RMS size of the PV current as a function of the temperature
difference, finding an effect ~pA.
