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  • Open Access

Resisting High-Energy Impact Events through Gap Engineering in Superconducting Qubit Arrays

Matt McEwen1,*,†, Kevin C. Miao1,†, Juan Atalaya1, Alexander Bilmes1, Alex Crook1, Jenna Bovaird1, John Mark Kreikebaum1, Nicholas Zobrist1, Evan Jeffrey1 et al.

Bicheng Ying1, Andreas Bengtsson1, Hung-Shen Chang1, Andrew Dunsworth1, Julian Kelly1, Yaxing Zhang1, Ebrahim Forati1, Rajeev Acharya1, Justin Iveland1, Wayne Liu1, Seon Kim1, Brian Burkett1, Anthony Megrant1, Yu Chen1, Charles Neill1, Daniel Sank1, Michel Devoret1,2, and Alex Opremcak1,†

  • *Contact author: mmcewen@google.com
  • †These authors contributed equally to this Letter.
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Phys. Rev. Lett. 133, 240601 – Published 9 December, 2024

DOI: https://doi.org/10.1103/PhysRevLett.133.240601

Abstract

Quantum error correction (QEC) provides a practical path to fault-tolerant quantum computing through scaling to large qubit numbers, assuming that physical errors are sufficiently uncorrelated in time and space. In superconducting qubit arrays, high-energy impact events can produce correlated errors, violating this key assumption. Following such an event, phonons with energy above the superconducting gap propagate throughout the device substrate, which in turn generate a temporary surge in quasiparticle (QP) density throughout the array. When these QPs tunnel across the qubits’ Josephson junctions, they induce correlated errors. Engineering different superconducting gaps across the qubit’s Josephson junctions provides a method to resist this form of QP tunneling. By fabricating all-aluminum transmon qubits with both strong and weak gap engineering on the same substrate, we observe starkly different responses during high-energy impact events. Strongly gap engineered qubits do not show any degradation in T1 during impact events, while weakly gap engineered qubits show events of correlated degradation in T1. We also show that strongly gap engineered qubits are robust to QP poisoning from increasing optical illumination intensity, whereas weakly gap engineered qubits display rapid degradation in coherence. Based on these results, gap engineering mitigates the threat of high-energy impacts to QEC in superconducting qubit arrays.

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Phys. Rev. Lett. 133, 240601– Published 9 December, 2024
  • Received 16 April 2024
  • Accepted 3 October 2024
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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