Hannah Stickler

Directional emission of a readout resonator for qubit measurement

  1. Alec Yen,
  2. Yufeng Ye,
  3. Kaidong Peng,
  4. Jennifer Wang,
  5. Gregory Cunningham,
  6. Michael Gingras,
  7. Bethany M. Niedzielski,
  8. Hannah Stickler,
  9. Kyle Serniak,
  10. Mollie E. Schwartz,
  11. and Kevin P. O'Brien
We propose and demonstrate transmission-based dispersive readout of a superconducting qubit using an all-pass resonator, which preferentially emits readout photons toward the output.
This is in contrast to typical readout schemes, which intentionally mismatch the feedline at one end so that the readout signal preferentially decays toward the output. We show that this intentional mismatch creates scaling challenges, including larger spread of effective resonator linewidths due to non-ideal impedance environments and added infrastructure for impedance matching. A future architecture using multiplexed all-pass readout resonators would avoid the need for intentional mismatch and potentially improve the scaling prospects of quantum computers. As a proof-of-concept demonstration of „all-pass readout,“ we design and fabricate an all-pass readout resonator that demonstrates insertion loss below 1.17 dB at the readout frequency and a maximum insertion loss of 1.53 dB across its full bandwidth for the lowest three states of a transmon qubit. We demonstrate qubit readout with an average single-shot fidelity of 98.1% in 600 ns; to assess the effect of larger dispersive shift, we implement a shelving protocol and achieve a fidelity of 99.0% in 300 ns.
arxiv pdf

Synchronous Detection of Cosmic Rays and Correlated Errors in Superconducting Qubit Arrays

  1. Patrick M. Harrington,
  2. Mingyu Li,
  3. Max Hays,
  4. Wouter Van De Pontseele,
  5. Daniel Mayer,
  6. H. Douglas Pinckney,
  7. Felipe Contipelli,
  8. Michael Gingras,
  9. Bethany M. Niedzielski,
  10. Hannah Stickler,
  11. Jonilyn L. Yoder,
  12. Mollie E. Schwartz,
  13. Jeffrey A. Grover,
  14. Kyle Serniak,
  15. William D. Oliver,
  16. and Joseph A. Formaggio
Quantum information processing at scale will require sufficiently stable and long-lived qubits, likely enabled by error-correction codes. Several recent superconducting-qubit experiments,
however, reported observing intermittent spatiotemporally correlated errors that would be problematic for conventional codes, with ionizing radiation being a likely cause. Here, we directly measured the cosmic-ray contribution to spatiotemporally correlated qubit errors. We accomplished this by synchronously monitoring cosmic-ray detectors and qubit energy-relaxation dynamics of 10 transmon qubits distributed across a 5x5x0.35 mm3 silicon chip. Cosmic rays caused correlated errors at a rate of 1/(10 min), accounting for 17±1% of all such events. Our qubits responded to essentially all of the cosmic rays and their secondary particles incident on the chip, consistent with the independently measured arrival flux. Moreover, we observed that the landscape of the superconducting gap in proximity to the Josephson junctions dramatically impacts the qubit response to cosmic rays. Given the practical difficulties associated with shielding cosmic rays, our results indicate the importance of radiation hardening — for example, superconducting gap engineering — to the realization of robust quantum error correction.
arxiv pdf