Performance Optimization for Drift-Robust Fidelity Improvement of Two-Qubit Gates

G.A.L. White, C.D. Hill, and L.C.L. Hollenberg
Phys. Rev. Applied 15, 014023 – Published 13 January 2021

Abstract

Quantum-system characterization techniques represent the front line in the identification and mitigation of noise in quantum computing but can be expensive in terms of quantum resources and time to repeatedly employ. Another challenging aspect is that the parameters governing the performance of various operations tend to drift over time and monitoring these is hence a difficult task. One of the most promising characterization techniques, gate-set tomography (GST), provides a self-consistent estimate of the completely positive trace-preserving (CPTP) maps for a complete set of gates, as well as preparation and measurement operators. We develop a method for performance optimization seeded by tomography (POST), which couples the power of GST with a classical optimization routine to achieve a consistent gate improvement in just a short number of steps within a given calibration cycle. By construction, the POST procedure finds the best available gate operation given the hardware and is therefore robust to the effects of drift. Further, in comparison to other quantum error-mitigation techniques, it builds upon a one-time application of GST. To demonstrate the performance of this method on a real quantum computer, we map out the operations of six qubit pairs on the superconducting ibmq_poughkeepsie quantum device. Under the restriction of logical-only control, we monitor the performance of the POST approach on a chosen controlled-not (cnot) gate over a period of six weeks. In this time, we achieve a consistent improvement in gate fidelity, averaging a fidelity increase of 21.1% as measured by randomized benchmarking. The POST approach should find wide applicability as it is hardware agnostic and can be applied at the upper logical level or at a deeper pulse-control level.

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  • Received 23 January 2020
  • Revised 22 September 2020
  • Accepted 6 November 2020

DOI:https://doi.org/10.1103/PhysRevApplied.15.014023

© 2021 American Physical Society

Physics Subject Headings (PhySH)

Quantum Information, Science & Technology

Authors & Affiliations

G.A.L. White1, C.D. Hill1,2, and L.C.L. Hollenberg1,*

  • 1School of Physics, University of Melbourne, Parkville, Victoria 3010, Australia
  • 2School of Mathematics and Statistics, University of Melbourne, Parkville, Victoria 3010, Australia

  • *lloydch@unimelb.edu.au

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Vol. 15, Iss. 1 — January 2021

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