Characterizing Spurious Mode Coupling in Superconducting Qubits

Superconducting circuits are a leading candidate for utility-scale quantum computing. Continued progress requires understanding and mitigating qubit decoherence. In state-of-the-art qubits, loss is dominated by defects residing at amorphous interfaces. However, as progress is made to reduce interface loss and as multiqubit processors grow in size, coupling to other spurious modes will play an increasingly significant role. Here, we characterize the coupling of transmon qubits to spurious chip and package modes. We describe optimal design and mitigation strategies to reduce coupling to these modes.