Behavior of noise in a nondegenerate Josephson-parametric amplifier

A systematic study of noise in a nondegenerate Josephson-parametric amplifier as it passes through the threshold for oscillation was performed. Below the threshold all the noise is accounted for by equilibrium fluctuations of the losses. Well above the threshold the noise is 3 dB larger than the below-threshold value and is again accounted for by noise from the losses. In the region near the threshold, the noise can become quite large. The behavior of the noise is in qualitative agreement with that expected for a generic system undergoing a Hopf bifurcation.