Superconducting Non-reciprocal Bandpass Filter Based on Spatio-Temporal Inductance Modulation
We present a non-magnetic, fully-integrated, superconducting non-reciprocal bandpass filter using spatio-temporal inductance modulation in coupled resonator networks, thus combining the functionalities of a conventional bandpass filter with an isolator. The bandpass filter is based on a capacitively-coupled shunt resonator architecture where the resonators are implemented as a parallel combination of finger capacitors and a chain of 10 SQUIDs which behave as flux-controlled nonlinear inductors. The operation principle of the device has been studied and optimized for non-reciprocal performance using Floquet spectral analysis where the time-modulated SQUIDs are modeled using frequency translational admittance matrices. The bandpass filter is implemented in a single-layer superconducting process. Operating at a base temperature of 20 mK, we measured a low insertion loss of 1.3 dB in the forward direction. In the reverse direction, the measured isolation is as high as +25 dB at the center frequency and >+15 dB across a bandwidth of 250 MHz.