Regensburg 2022 – scientific programme
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QI: Fachverband Quanteninformation
QI 13: Implementations: Superconducting Qubits
QI 13.11: Talk
Friday, September 9, 2022, 12:30–12:45, H8
Mitigation of quasiparticle loss in superconducting qubits by phonon scattering — Arno Bargerbos1, Lukas J. Splitthoff1, Marta Pita-Vidal1, Jaap J. Wesdorp1, Yu Liu2, Peter Krogstrup3, Leo P. Kouwenhoven1, Christian K. Andersen1, and •Lukas Grünhaupt1,4 — 1QuTech and Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands — 2Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark — 3Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark — 4Physikalisch-Technische Bundesanstalt, Braunschweig, Germany
Most error correction schemes for future quantum processors rely on the assumption that errors are uncorrelated. However, in superconducting devices this assumption is drastically violated in the presence of ionizing radiation, which creates bursts of high energy phonons in the substrate. A mitigation technique is to place large volumes of metal on the device, capable of reducing the phonon energy to below the superconducting gap of the qubits. To investigate the effectiveness of this method we fabricate a device with four nominally identical nanowire-based transmon qubits and replace one half of the niobium titanium nitride ground plane with aluminum (Al), which has a much lower superconducting gap. We inject phonons into the substrate by voltage biasing a galvanically isolated Josephson junction and we find protection due to the Al by a factor of 2-4 in terms of qubit lifetime and excited state population. Furthermore, we turn the Al normal with a magnetic field, finding no marked change in the phonon-protection.