Frequency-conversion loss in three-wave-mixing traveling-wave parametric amplifiers

Traveling-Wave Parametric Amplifiers (TWPAs) are one of the leading technologies for the amplification of weak microwave signals with wide bandwidth and high saturation power while keeping the added noise close to the quantum limit. One design goal in the development of TWPAs is the reduction of insertion loss, which decreases the achievable signal gain and limits the attainable signal to noise ratio. Commonly, dielectric loss is seen as one of the major contributors to the insertion loss. Here we discuss another loss mechanism in metamaterials with a strong second-order nonlinearity, such as three-wave-mixing TWPAs. We show that low-frequency noise of high-enough amplitude can lead to frequency-conversion of weak probe-tones and easily dominate over other loss sources. This loss mechanism due to nonlinearity appears as linear loss and can therefore lead to false conclusions in the characterization of TWPAs.