Paul G. Baity

Modeling Phonon-mediated Quasiparticle Poisoning in Superconducting Qubit Arrays

  1. Eric Yelton,
  2. Clayton P. Larson,
  3. Vito Iaia,
  4. Kenneth Dodge,
  5. Guglielmo La Magna,
  6. Paul G. Baity,
  7. Ivan V. Pechenezhskiy,
  8. Robert McDermott,
  9. Noah Kurinsky,
  10. Gianluigi Catelani,
  11. and Britton L. T. Plourde
Correlated errors caused by ionizing radiation impacting superconducting qubit chips are problematic for quantum error correction. Such impacts generate quasiparticle (QP) excitations
in the qubit electrodes, which temporarily reduce qubit coherence significantly. The many energetic phonons produced by a particle impact travel efficiently throughout the device substrate and generate quasiparticles with high probability, thus causing errors on a large fraction of the qubits in an array simultaneously. We describe a comprehensive strategy for the numerical simulation of the phonon and quasiparticle dynamics in the aftermath of an impact. We compare the simulations with experimental measurements of phonon-mediated QP poisoning and demonstrate that our modeling captures the spatial and temporal footprint of the QP poisoning for various configurations of phonon downconversion structures. We thus present a path forward for the operation of superconducting quantum processors in the presence of ionizing radiation.
arxiv pdf

Circle fit optimization for resonator quality factor measurements: point redistribution for maximal accuracy

  1. Paul G. Baity,
  2. Connor Maclean,
  3. Valentino Seferai,
  4. Joe Bronstein,
  5. Yi Shu,
  6. Tania Hemakumara,
  7. and Martin Weides
The control of material loss mechansims is playing an increasingly important role for improving coherence times in superconducting quantum devices. Such material losses can be characterized
through the measurement of planar superconducting resonators, which reflect losses through the resonance’s quality factor Ql. The resonance quality factor consists of both internal (material) losses as well as coupling losses when resonance photons escape back into the measurement circuit. The combined losses are then described as Q−1l=Q−1c+Q−1i, where Qc and Qi reflect the coupling and internal quality factors of the resonator, respectively. To separate the relative contributions of Qi and Qc to Ql, diameter-correcting circle fits use algebraic or geometric means to fit the resonance signal on the complex plane. However, such circle fits can produce varied results, so to address this issue, we use a combination of simulation and experiment to determine the reliability of a fitting algorithm across a wide range of quality factor values from Qi≪Qc to Qc≪Qi. In addition, we develop a novel measurement protocol that can not only reduce fitting errors by factors ≳2 but also mitigates the influence of the measurement background on the fit results. This technique can be generalized for other resonance systems beyond superconducting resonators.
arxiv pdf