Proposal for a novel directional parametric amplifier requiring no external nonreciprocal components*

Quantum-limited Josephson parametric amplifiers are an important part of most superconducting qubit readout systems. Parametric amplifiers typically operate in reflection and require external nonreciprocal devices to spatially separate the input and output fields of the amplifier and to protect the qubit from noise propagating from the output field. To achieve this without additional external components, the parametric amplifier should have a matched input port, large forward gain from input to output, ideally zero reverse gain from output to input, a matched output port, and an auxiliary port which provides amplified quantum noise to the output. We propose a novel four-port phase-preserving parametric amplifier that satisfies all of the above requirements. This proposal is a natural extension of the previously realized three-port directional amplifier, but does not require an isolator on its output. We discuss the properties of this proposal, and we present a possible experimental implementation.