Noise and Power handling of the Inelastic Cooper-pair Tunneling Amplifier (ICTA)

Readout of superconducting qubits requires microwave amplifiers with added noise as close as possible to the quantum limit. This limit is now routinely approached by Josephson parametric amplifiers (JPAs). However, generation, routing and filtering of the strong microwave pump, which powers them, require significant hardware overhead and can affect the device under test. DC-powered amplifiers, on the other hand, are much easier to use 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 achieved exactly that with the "inelastic Cooper-pair tunneling amplifier" [1]. It is based on a voltage-biased Josephson junction, where the energy 2eV of a tunneling Cooper pair plays the role of a pump photon. We have demonstrated added noise at the quantum limit within measurement accuracy and we discuss here saturation and the influence of voltage bias noise.

[1] Jebari, S. et al. Near-quantum-limited amplification from inelastic Cooper-pair tunnelling. Nat Electron 1, 223–227 (2018)