Non-linear amplification in Inelastic Cooper-pair Tunneling Amplifiers (ICTA)

Josephson parametric amplifiers can work as linear amplifier with added noise at the quantum limit. The Inelastic Cooper-pair Tunneling Amplifier (ICTA) works according to the same principle, but uses a DC bias instead of the strong microwave pump needed for the parametric amplification, which greatly reduces the hardware overhead required to operate the amplifier. It replaces the pump photon by the energy 2eV of a Cooper pair tunneling through a Josephson junction biased at a DC voltage V. While for linear amplification this energy corresponds to the creation of one photon in both the signal and idler mode, we have also observed processes with multiple photons being created in one of the modes. The dominant process can easily be selected by tuning the DC bias. Here we discuss how these processes with nonlinear gain characteristics could be used advantageously in state discrimination.