Quantum effects in cryogenic microwave voltage amplifiers

Abstract

It is shown that in cryogenic microwave voltage amplifiers the standard definition of the noise figure F can be used and that it leads to the classical result without quantum effects. However, the available output noise power P av of such an amplifier with available gain G av is found to be FkTΔfG av( E kT ) , where E = 1 2 hf + hf [ exp ( hf kT ) − 1] is the average energy of an harmonic oscillator of frequency f at the temperature T and E kT is the quantum correction factor for thermal nose and shot noise. A discussion shows that this quantum effect might be measurable at 50–100 GHz and T = 4-2° K.