Design of an on-chip superconducting microwave circulator with octave bandwidth

Standard techniques for the measurement of superconducting qubits rely on non-reciprocal devices like circulators to isolate sensitive quantum circuits and/or duplex parametric amplifiers. Commercial ferrite circulators are broadband, but are also bulky and lossy, and cannot be easily miniaturized as superconducting circuits because of their large permanent magnets. Here we present the design of a broadband, superconducting, on-chip circulator composed of dynamically modulated transfer switches and delays. Design goals are set for the multiplexed readout of superconducting qubits, and for integration with broadband quantum limited amplifiers. Simulations of the device with realistic parameters show that it allows for low-loss circulation (insertion loss < 0.35 dB and isolation > 20 dB) over an instantaneous bandwidth of 2.3 GHz. As the device is estimated to be linear for input powers up to -65 dBm, this design improves on the bandwidth and power-handling of previous superconducting circulators by over a factor of 50.