Phonon bursts in the substrate of a superconducting qubit array with energy above the superconducting gap can produce dissipative quasiparticle excitations in the electrodes of many qubits on a chip, leading to correlated errors between qubits. Mitigating such errors is challenging for quantum error correcting codes when the correlations extend across a significant fraction of the qubits in the array. Phonon bursts and the ensuing quasiparticle poisoning can be caused by ionizing radiation impacts in the device substrate. Phonon-only events without a corresponding charge signal can also be produced through mechanical relaxation processes in the device. We characterize this poisoning and strategies for mitigation through measurements of quasiparticle charge-parity switching, qubit relaxation, and offset-charge shifts. We use a variety of techniques to produce the phonon bursts, including irradiation with gamma-ray sources, direct injection of phonons with on-chip tunnel junctions and focused optical pulses, and controlled mechanical vibrations.
Britton Plourde, Professor, University of Wisconsin-Madison
Host: Venkat Chandrasekhar
Joan West
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