Integrating low-loss magnetic couplers with superconducting 3d-cavities*

Superconducting circuits are a leading platform for realizing intermediate scale quantum information processing. In particular, the modular approach distributes entanglement over a network of superconducting cavities, limiting the unwanted coupling between high-fidelity modules. As the scale of such networks increases, it is becoming essential to route and reroute signals with high fidelity. We present a design to magnetically couple cavities to the network via balanced superconducting switches, whose coupling strength can be varied to change the connectivity of a network. We exploit the differential nature of magnetic coupling to adapt to the balanced switch. We reduce seam loss by constructing the cavities and the wiring ground plane from the same piece of metal. Finally, we reduce packaging loss by eliminating circuit boards, wirebonds, and microwave connectors in the signal path. Simulation of this design predicts that it can provide sufficient coupling rate while introducing minimal loss, making it a suitable building block for the larger quantum network.