Phonons, Quasiparticles, and Correlated Errors in Superconducting Qubits
Britton Plourde | University of Wisconsin–Madison
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.
IQC faculty host: Adrian Lupascu
Location
QNC 0101
About the speaker
Britton Plourde received a Ph.D. in physics from the University of Illinois at Urbana-Champaign in 2000 studying vortex dynamics in superconductors. From 2000 to 2004, he was a postdoctoral scholar at the University of California, Berkeley where he worked on experiments with superconducting flux qubits. He was on the faculty at Syracuse University since 2005 where he established a low-temperature research lab investigating various aspects of superconducting circuits for quantum information processing.
Plourde joined the faculty at the University of Wisconsin-Madison in 2024 and also started working with Qolab, a Madison-based quantum computing startup company. Some of his key contributions to the field include investigations of decoherence mechanisms and mitigation techniques for improved qubit performance and development of tools for scalable qubit control and readout. He is a Fellow of IEEE and the American Physical Society, and he received a CAREER award from the NSF and an IBM Faculty Award.