Mitigating losses of superconducting qubits strongly coupled to defect modes

The dominant contribution to the energy relaxation of state-of-the-art superconducting qubits is often attributed to their coupling to an ensemble of material defects which behave as two-level systems. These defects have varying microscopic characteristics which result in a wide range of observable defect properties such as resonant frequencies, coherence times, and coupling rates to qubits $g$. Here, we investigate strategies to mitigate losses to the family of defects that strongly couple to qubits ($g/2\ensuremath{\pi}\ensuremath{\ge}0.5\mathrm{M}\mathrm{Hz}$). Such strongly coupled defects occur more rarely and are particularly detrimental to the qubit coherence when resonant with the qubit, and to the fidelities of operations relying on frequency excursions, such as flux-activated two-qubit gates. To assess their impact, we perform swap spectroscopy on 92 frequency-tunable qubits and quantify the spectral density of these strongly coupled modes. We show that the frequency configuration of the defects is rearranged by warming the sample to room temperature, whereas the total number of defects on a processor tends to remain constant. We then explore methods for fabricating qubits with a reduced number of strongly coupled defect modes by systematically measuring their spectral density for decreasing Josephson junction dimensions and for various surface cleaning methods. Our results provide insights into the properties of strongly coupled defect modes and show the benefits of minimizing Josephson junction dimensions to improve qubit properties.

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Publication Details

Journal
Physical Review Applied
Published
2025-04-24
DOI
https://doi.org/10.1103/physrevapplied.23.044054
Citations
10
Primary Topic
Quantum and electron transport phenomena
Type
article
Field-Weighted Citation Impact
12.47

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article

Mitigating losses of superconducting qubits strongly coupled to defect modes

Quentin Ficheux, Graham J. Norris, K. Hanke, Andreas J. Wallraff et al.
10 citations
Physical Review Applied
Quantum and electron transport phenomena
12.47
article

Mitigating losses of superconducting qubits strongly coupled to defect modes

Quentin Ficheux, Graham J. Norris, K. Hanke, Andreas J. Wallraff, Alexander Flasby, Colin Scarato, Michael Kerschbaum, Stefania Lazăr, Christoph Hellings, Nathan Lacroix, Jean-Claude Besse, François Swiadek, Sebastian Krinner, Ants Remm, Mohsen Bahrami Panah, Alexei Orekhov, Dante Colao Zanuz, Christopher Eichler, Laurent Michaud
article en
10 citations

Abstract

The dominant contribution to the energy relaxation of state-of-the-art superconducting qubits is often attributed to their coupling to an ensemble of material defects which behave as two-level systems. These defects have varying microscopic characteristics which result in a wide range of observable defect properties such as resonant frequencies, coherence times, and coupling rates to qubits $g$. Here, we investigate strategies to mitigate losses to the family of defects that strongly couple to qubits ($g/2\ensuremath{\pi}\ensuremath{\ge}0.5\mathrm{M}\mathrm{Hz}$). Such strongly coupled defects occur more rarely and are particularly detrimental to the qubit coherence when resonant with the qubit, and to the fidelities of operations relying on frequency excursions, such as flux-activated two-qubit gates. To assess their impact, we perform swap spectroscopy on 92 frequency-tunable qubits and quantify the spectral density of these strongly coupled modes. We show that the frequency configuration of the defects is rearranged by warming the sample to room temperature, whereas the total number of defects on a processor tends to remain constant. We then explore methods for fabricating qubits with a reduced number of strongly coupled defect modes by systematically measuring their spectral density for decreasing Josephson junction dimensions and for various surface cleaning methods. Our results provide insights into the properties of strongly coupled defect modes and show the benefits of minimizing Josephson junction dimensions to improve qubit properties.

Physical Review AppliedVol. 23(4)
Paul Scherrer Institute (CH), ETH Zurich (CH)
Office of the Director of National Intelligence, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Baugarten Stiftung, Intelligence Advanced Research Projects Activity, National Center of Competence in Research Quantum Science and Technology, Army Research Office
Climate action
Openalex Percentile: Top 1%
Quantum and electron transport phenomena
12.47
DOISourceOpenAlex
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