Observation of photon noise by cold-electron bolometers

We have observed the photon noise by measuring a response to the black body 350 GHz radiation and noise of the cold-electron bolometers (CEBs). The experimental results have been fit to the theoretical model of CEBs with two heat-balance equations. The measured noise has been decomposed into several terms with the help of theory. It is demonstrated that the photon noise exceeds any other noise components, which allows us to conclude that the bolometers measure the photon noise. Moreover, a peculiar shape of the noise dependence on the absorbed power originates completely from the photonic component according to the theory. In the additional experiment on heating of the cryostat plate together with the sample holder, we have observed the near independence of the noise on the electron temperature of the absorber, which has provided another proof of the presence of the photon noise in the first experiment. The least ratio between internal and photon noise equivalent powers, observed in our experiments, is 1.1 for the absorbed power of 1-2 pW