Broadband On-chip Magnetless Isolation

Isolators are commonly found in the microwave amplification chain of cryogenic set-ups to shield the device-under-test, qubits in particular, from noise and back-scattered signals. However, conventional ferrite-based isolators are bulky, lossy, and rely on strong magnetic fields, which prevent their co-integration with superconducting circuits. Other magnetless alternatives have been proposed but their implementations are limited in terms of power dissipation, isolation, insertion loss, or isolation bandwidth. Here, we present a novel magnetless isolator architecture that overcomes these limitations. Our proposal uses a transmission line with Superconducting Quantum Interference Devices (SQUIDs) that are flux-modulated by an adjacent pump line to obtain nonreciprocal parametric conversion and/or amplification. Through dispersion engineering and an optimized modulation scheme, we show through simulations that the proposed architecture can provide 20dB isolation over an instantaneous bandwidth of 4GHz. Our work demonstrates the potential of a broadband on-chip magnetless isolator which would pave the way towards large-scale integration with superconducting quantum processors.