Implementation of a Broadband Superconducting Qubit-Compatible Microwave Isolator

We present a practical design of a proposed scheme for broadband microwave isolation that uses adiabatic parametric mode conversion in a pair of coupled nonlinear transmission lines [1]. This design utilizes a flip-chip configuration in the standard aluminum fabrication process allowing for negligible insertion loss and direct integration with the superconducting quantum circuits. Combining linear and nonlinear adiabatic mode conversion in the design, we expect to get more than 3 GHz bandwidth of isolation centered at 6 GHz. We discuss various aspects of the design such as implementing the spatial phase-mismatch and nonlinear coupling variations and mitigating the unwanted couplings. We also present preliminary experimental results.

[1] M. Naghiloo, K. Peng, Y. Ye, G. Cunningham, and K. P. O’Brien, Broadband microwave isolation with adiabatic mode conversion in coupled superconducting transmission lines, ArXiv:2103.07793 (2021)