Realization of Cold-Electron Bolometers with Ultimate Sensitivity Due to Strong Electron Self-Cooling

We have realized an ultimate photon-noise-limited array of cold-electron bolometers (CEBs) for OLIMPO Balloon Telescope. The CEB array demonstrates very effective electron self-cooling of the absorber from 310 mK to 100 mK without optical power load, P0, and from 310 mK to 160 mK with P0= 20 pW at 345 GHz. Due to this effective electron cooling acting as strong electrothermal feedback, the ultimate photon-noise-limited mode of operation is realized in the range of P0 starting from 8 pW and up to P0=20 pW at Tph=330 mK. To our knowledge, there is no analog in the world for bolometers working at electron temperature less than phonon temperature.