Optimizing rf-SQUID Parametric Amplifiers for High Saturation Power

Superconducting quantum computers are quickly scaling to many physical qubits, each requiring quantum-limited first stage amplifiers which support high fidelity readout. Such readout, to evade qubit decay, is necessarily fast and, for each qubit, uses large photon numbers in a short-lifetime cavity, which in turn requires a relatively broadband (10s of MHz) and high saturation first stage amplifier. This work focuses on the optimization of saturation power in three-wave-mixing degenerate parametric amplifiers based on arrayed rf-SQUIDs. We test for optimal amplifier saturation and intermodulation distortion, which determine the performance and suitability for multi-channel operation of our amplifiers as a function of the varying ratio of linear shunt inductance to Josephson inductance in our arrayed rf-SQUIDs. We will discuss results from several recent designs of amplifiers, and examine the tradeoffs between tunability, pump power, and saturation power/distortion in our devices from the perspective of both few-qubit laboratory scale experiments and large-scale quantum information processors.