Engineering Phonon Isolation in SOI Superconducting Qubits for Radiation-Resilient Quantum Hardware.

Superconducting qubits are highly susceptible to quasiparticle generation from background ionizing radiation, which produces energetic phonons capable of breaking Cooper pairs and inducing correlated errors. Following the observation of cosmic-ray induced error bursts in large-scale superconducting qubit arrays [1], recent efforts have explored radiation abatement through phonon down conversion, material optimization, and underground operation [2,3]. However, scalable on-chip suppression of phonon-mediated quasiparticles remains an open challenge.

In this work, we present the design and fabrication of Transmon qubits on a silicon-on-insulator (SOI) platform incorporating a suspended membrane that acts as an acoustic low-pass filter. This architecture enables systematic investigation of phonon transport and its role in radiation-induced decoherence. We report successful fabrication and characterization of SOI-based Transmon, demonstrating compatibility of membrane-supported architectures with standard superconducting qubit processes and operation. Future work will focus on comparative surface and underground measurements to quantify radiation-induced decoherence and validate the proposed phonon-isolation approach.

[1]: McEwen, M., Faoro, L., Arya, K. et al. Resolving catastrophic error bursts from cosmic rays in large arrays of superconducting qubits. Nat. Phys. 18, 107–111 (2022).

[2]: Loer, B., et al. Abatement of ionizing radiation for superconducting quantum devices. Nat. Commun. 15, (2024).

[3]:Bargerbos, A., et al. Mitigation of quasiparticle loss in superconducting qubits by phonon scattering. Phys. Rev. Lett. 131, (2023).