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  • Featured in Physics
  • Open Access

Correlated Phase Error Bursts in a Gap-Engineered Superconducting Qubit Array

Vladislav D. Kurilovich*,†, Gabrielle Roberts*,‡, Leigh S. Martin, Matt McEwen, Alec Eickbusch, Lara Faoro, Lev B. Ioffe, Juan Atalaya, Alexander Bilmes et al.

John Mark Kreikebaum, Andreas Bengtsson, Paul Klimov, Matthew Neeley, Wojciech Mruczkiewicz, Kevin Miao, Igor L. Aleiner, Julian Kelly, Yu Chen, Kevin Satzinger, and Alex Opremcak*,§

  • *These authors contributed equally to this work.
  • †Contact author: vladkurilovich@google.com
  • ‡Contact author: gabriellelcr@google.com
  • §Contact author: opremcak@google.com
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Phys. Rev. X 16, 021025 – Published 4 May, 2026

DOI: https://doi.org/10.1103/1bl4-b2f7

Abstract

One of the roadblocks toward the implementation of a fault-tolerant superconducting quantum processor is impacts of ionizing radiation with the qubit substrate. Such impacts temporarily elevate the density of quasiparticles (QPs) across the device, leading to correlated qubit error bursts. The most damaging errors, T1 errors, stem from QP tunneling across the qubit Josephson junctions (JJs). Recently, we demonstrated [M. McEwen, K. Miao, et al., Phys. Rev. Lett. 133, 240601 (2024)] that this type of error can be strongly suppressed by engineering the profile of superconducting gap at the JJs in a way that prevents QP tunneling. In this work, we identify a new type of impact-induced correlated error that persists in the presence of gap engineering. We observe that impacts shift the frequencies of the affected qubits, and thus lead to correlated phase errors. The frequency shifts are systematically negative, reach values up to 3 MHz, and last for ∼1  ms. We provide evidence that the shifts originate from QP-qubit interactions in the JJ region. Further, we demonstrate that the shift-induced phase errors can be detrimental to the performance of quantum error correction protocols.

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Physics Subject Headings (PhySH)

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Quantum Error Correction Faces Another Hurdle

Published 4 May, 2026

Newly identified correlated errors in superconducting qubits could limit the performance of error-correction schemes needed for a practical quantum computer.

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Popular Summary

Ionizing radiation is a long-standing nemesis of superconducting quantum processors. Impacts of high-energy radiation break electron pairs responsible for superconductivity, causing a large number of qubits to fail simultaneously. Such correlated error bursts are particularly dangerous because they overwhelm standard quantum error correction protocols. Until recently, the most damaging bursts involved qubits relaxing their energy into a bath of unpaired electrons. A hardware modification, known as “gap engineering,” successfully suppressed this burst type. However, did this modification solve the radiation problem completely? In this work, we experimentally discover a type of correlated error that persists even in gap-engineered processors, namely, phase error bursts. These bursts result from the shifts in the qubit frequencies that inevitably occur when superconducting electron pairs are broken. Our findings show that the realization of a fault-tolerant quantum computer will require developing new mitigation strategies to suppress the residual phase errors.

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Phys. Rev. X 16, 021025– Published 4 May, 2026
  • Received 7 July 2025
  • Accepted 3 March 2026
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