Multiparametric Amplification and Qubit Measurement with a Kerr-free Josephson Ring Modulator

Josephson-junction based parametric amplifiers have become a ubiquitous component in superconducting quantum machines. Although parametric amplifiers regularly achieve near-quantum limited performance, they have many limitations, including low saturation powers, lack of directionality, and narrow bandwidth. The first is believed to stem from the higher order Hamiltonian terms endemic to Josephson junction circuits, and the latter two are direct consequences of the nature of the parametric interactions which power them. In this work, we attack both of these issues. First, we have designed a new, linearly shunted Josephson ring modulator (JRM), which nearly nullifies all fourth-order terms at a single flux bias point. Next, we achieve gain through a pair of balanced parametric drives. When applied separately, these drives produce phase-preserving gain (G) and gainless photon conversion (C); when applied together, the resultant amplifier (which we term GC) is a bidirectional, phase-sensitive, transmission-only amplifier with a large, gain-independent bandwidth. Finally, we have demonstrated the practical utility of the GC amplifier, as well as its quantum efficiency, by using it to read out a superconducting transmon qubit.