Advances in cavity-based parametric amplification

Cavity-based parametric amplifiers, which typically amplify quantum signals in reflection, have long offered superior noise performance for measuring objects like qubits. Recently, the field has developed techniques to also achieve high saturation power as well, albeit at the cost of similarly increased pump powers. In this talk, I'll review our progress in addressing three remaining issues: pump-power efficiency, instantaneous bandwidth, and the lack of directional gain which in turn requires us to use circulators in our readout chains. We are improving pump power efficiency by deliberately shaping the device's nonlinearity to convert a larger fraction of pump photons to amplified output photons while retaining a linear signal response [Hougland et al., PRA (2025)]. We are addressing the second challenge by adding an engineered filter between the amplifier 'core' and input port to broaden the instantaneous bandwidth [Naaman and Aumentado, PRX Quantum (2022)]. For directionality, we are exploring the realization of an embedded amplifier which uses a sequence of parametric interactions among modes in direct contact with the qubit readout mode to both transfer light from the readout cavity to a nonlinear SNAIL mode, amplify it, and finally transfer signal to a very low Q output mode, emitting a pre-amplified readout tone from the device while avoiding back-action on the qubit and its readout cavity.