Mohsen Bahrami Panah

Fast Flux-Activated Leakage Reduction for Superconducting Quantum Circuits

  1. Nathan Lacroix,
  2. Luca Hofele,
  3. Ants Remm,
  4. Othmane Benhayoune-Khadraoui,
  5. Alexander McDonald,
  6. Ross Shillito,
  7. Stefania Lazar,
  8. Christoph Hellings,
  9. Francois Swiadek,
  10. Dante Colao Zanuz,
  11. Alexander Flasby,
  12. Mohsen Bahrami Panah,
  13. Michael Kerschbaum,
  14. Graham J. Norris,
  15. Alexandre Blais,
  16. Andreas Wallraff,
  17. and Sebastian Krinner
Quantum computers will require quantum error correction to reach the low error rates necessary for solving problems that surpass the capabilities of conventional computers. One of the
dominant errors limiting the performance of quantum error correction codes across multiple technology platforms is leakage out of the computational subspace arising from the multi-level structure of qubit implementations. Here, we present a resource-efficient universal leakage reduction unit for superconducting qubits using parametric flux modulation. This operation removes leakage down to our measurement accuracy of 7⋅10−4 in approximately 50ns with a low error of 2.5(1)⋅10−3 on the computational subspace, thereby reaching durations and fidelities comparable to those of single-qubit gates. We demonstrate that using the leakage reduction unit in repeated weight-two stabilizer measurements reduces the total number of detected errors in a scalable fashion to close to what can be achieved using leakage-rejection methods which do not scale. Our approach does neither require additional control electronics nor on-chip components and is applicable to both auxiliary and data qubits. These benefits make our method particularly attractive for mitigating leakage in large-scale quantum error correction circuits, a crucial requirement for the practical implementation of fault-tolerant quantum computation.
arxiv pdf

Calibration of Drive Non-Linearity for Arbitrary-Angle Single-Qubit Gates Using Error Amplification

  1. Stefania Lazăr,
  2. Quentin Ficheux,
  3. Johannes Herrmann,
  4. Ants Remm,
  5. Nathan Lacroix,
  6. Christoph Hellings,
  7. Francois Swiadek,
  8. Dante Colao Zanuz,
  9. Graham J. Norris,
  10. Mohsen Bahrami Panah,
  11. Alexander Flasby,
  12. Michael Kerschbaum,
  13. Jean-Claude Besse,
  14. Christopher Eichler,
  15. and Andreas Wallraff
The ability to execute high-fidelity operations is crucial to scaling up quantum devices to large numbers of qubits. However, signal distortions originating from non-linear components
in the control lines can limit the performance of single-qubit gates. In this work, we use a measurement based on error amplification to characterize and correct the small single-qubit rotation errors originating from the non-linear scaling of the qubit drive rate with the amplitude of the programmed pulse. With our hardware, and for a 15-ns pulse, the rotation angles deviate by up to several degrees from a linear model. Using purity benchmarking, we find that control errors reach 2×10−4, which accounts for half of the total gate error. Using cross-entropy benchmarking, we demonstrate arbitrary-angle single-qubit gates with coherence-limited errors of 2×10−4 and leakage below 6×10−5. While the exact magnitude of these errors is specific to our setup, the presented method is applicable to any source of non-linearity. Our work shows that the non-linearity of qubit drive line components imposes a limit on the fidelity of single-qubit gates, independent of improvements in coherence times, circuit design, or leakage mitigation when not corrected for.
arxiv pdf