Nonreciprocal quantum information processing with superconducting diodes in circuit quantum electrodynamics

TL;DR

This paper introduces superconducting diodes as nonreciprocal elements in circuit QED, enabling high-fidelity quantum signal routing and nonreciprocal qubit interactions for advanced quantum networks.

Contribution

It proposes flux-controlled superconducting diodes as on-chip nonreciprocal components, demonstrating their use in nonreciprocal qubit coupling and quantum gate operations.

Findings

Flux bias induces direction-dependent resonance shifts.

Isolation ratio scales with multiple superconducting diodes.

Demonstrated nonreciprocal half-iSWAP gate between two qubits.

Abstract

Introducing new components and functionalities into quantum devices is critical in advancing state-of-the-art hardware. Here, we propose superconducting diodes (SDs) as a coherent nonreciprocal element in circuit quantum electrodynamics (cQED) architectures. In particular, we use an asymmetric SQUID as an SD controlled with a flux bias - nonreciprocal element with single control handle and on-chip modality. We spectroscopically characterize SD and show that flux bias acts cooperatively with the nonlinear diode response to induce direction-dependent resonance shifts in the transmission spectrum. We show that even with modest diode efficiency the isolation isolation ratio is sufficiently high, and scales with multiple SDs. We demonstrate the use of the SD as a coupler to realize coherent nonreciprocal qubit-qubit coupling. With a minimal two qubit system, we demonstrate nonreciprocal half-iSWAP, thereby showcasing the potential of intrinsic nonreciprocity as a tool to perform arbitrary two-qubit gates. Our work enables high-fidelity signal routing and entanglement generation in all-to-all connected microwave quantum networks, where nonreciprocity is embedded at the device level.