Mitigating Losses of Superconducting Qubits Strongly Coupled to Defect Modes

• URL: http://arxiv.org/abs/2407.18746v1
• Date: Fri, 26 Jul 2024 14:02:57 GMT
• Title: Mitigating Losses of Superconducting Qubits Strongly Coupled to Defect Modes
• Authors: Dante Colao Zanuz, Quentin Ficheux, Laurent Michaud, Alexei Orekhov, Kilian Hanke, Alexander Flasby, Mohsen Bahrami Panah, Graham J. Norris, Michael Kerschbaum, Ants Remm, François Swiadek, Christoph Hellings, Stefania Lazăr, Colin Scarato, Nathan Lacroix, Sebastian Krinner, Christopher Eichler, Andreas Wallraff, Jean-Claude Besse,
• Abstract summary: We investigate strategies to mitigate losses to the family of defects that strongly couple to qubits. We show that the frequency configuration of the defects is rearranged by warming up the sample to room temperature. We then explore methods for fabricating qubits with a reduced number of strongly coupled defect modes.
• Score: 28.49668795915129
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• 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 large 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 ($g/2\pi\ge$ 0.5 MHz). Such strongly coupled defects are particularly detrimental to the coherence of qubits 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 up 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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