Four-port directional parametric amplifier

Quantum limited parametric amplifiers based on Josephson junctions are important for measurement of superconducting qubits. Traditionally, these are reflection amplifiers which need external non-reciprocal elements to separate the input from the output. It is possible however, to make multi-mode circuits and drive multiple parametric processes together to achieve non-reciprocity. Three-mode devices based on these techniques that have been made so far have either lacked output matching or provide unity reverse gain, thus relying on perfectly well matched and thermalized output lines. Adding a fourth mode can solve these issues and can help us build a fully directional parametric amplifier. We present the design and experimental progress towards realizing such a four-mode device which under appropriate drive conditions would act like an amplifier which has appreciable forward gain, has perfect isolation, is input- and output-matched and has an auxiliary port which acts as the cold load.