Shot noise and photon-induced correlations in 500 GHz SIS detectors

Photon-induced current correlations in SIS detectors can result in an output noise that is greater or less than shot noise. Evidence of these correlations had been observed for 100 GHz rf by accurate noise measurements as reported in our previous work. We now present a detailed analysis of these current correlations for frequencies between 100 and 500 GHz. We also report new measurements of photon-induced noise in a 490 GHz SIS mixer, and discuss the Gaussian beam techniques used to eliminate the thermal background radiation. For small 490 GHz rf power, the output noise is equal to shot noise. The results of the 100 and 490 GHz photon noise measurement are summarized in context to shot noise and the effect of the current correlations predicted by the theoretical model.< >