Nonreciprocal microwave signal processing with a Field-Programmable Josephson Amplifier

We report on the design and implementation of a Field Programmable Josephson Amplifier (FPJA) - a compact and lossless superconducting circuit that can be programmed in situ by a set of microwave drives to perform reciprocal and nonreciprocal frequency conversion and amplification. In this work we demonstrate four modes of operation: frequency conversion $-0.5 dB$ transmission, $-30 dB$ reflection, circulation $-0.5 dB$ transmission, $-30 dB$ reflection, $30 dB$ isolation, phase-preserving amplification gain $>20 dB$, $1 photon$ of added noise and directional phase-preserving amplification $-10 dB$ reflection, $18 dB$ forward gain, $8 dB$ reverse isolation, $1 photon$ of added noise. The system exhibits quantitative agreement with theoretical prediction. Based on a gradiometric Superconducting Quantum Interference Device (SQUID) with Nb/Al-AlO_x/Nb Josephson junctions, the FPJA is first-order insensitive to flux noise and can be operated without magnetic shielding at low temperature. Due to its flexible design and compatibility with existing superconducting fabrication techniques, the FPJA offers a straightforward route toward on-chip integration with superconducting quantum circuits such as qubits or microwave optomechanical systems.