Gain and noise of the Inelastic Cooper-pair Tunneling Amplifier (ICTA)

While Josephson parametric amplifiers have added noise close to the quantum limit, they require a strong microwave pump that can affect the device under test and the generation, routing and filtering of this pump tone require significant hardware overhead. DC-powered amplifiers are much easier to use in that respect but have so far failed to approach the quantum limit because they could not be mapped to a parametric amplification scheme with a well-identified idler mode. We have demonstrated added noise at the quantum limit within measurement accuracy with the Inelastic Cooper-pair tunneling amplifier, a DC powered parametric amplifier with a well-identified idler mode, based on a voltage-biased Josephson junction where the energy 2eV of a tunneling Cooper pair plays the role of a pump photon. Here, we discuss how design parameters influence the saturation power as well as the highest achievable gain while maintaining quantum limited noise performance.