Zappe Photon Upconverters for Quantum Measurements of Low-Frequency Electrical Resonators, Part II: Implementation of the Prototype

We describe progress towards the first Zappe Photon Upconverter (ZPU), a Josephson-junction-based device capable of performing quantum mechanical readout protocols on low-frequency, lumped-element electromagnetic resonators. The prototype ZPU is being constructed using techniques similar to those used in superconducting transmon qubits, where the Josephson device is connected to a lithographed antenna immersed in the electromagnetic field of a three-dimensional microwave cavity. We describe the constraints on the circuit design and propose targets for the component values. We also present measurements of the quality factor of the superconducting microwave cavity designed for use with the first-generation ZPU, numerical modeling of the circuit parameters, and projections of the sensitivity enhancement available from backaction evading measurements using a prototype ZPU.