Universal gates for protected superconducting qubits using optimal control

Mohamed Abdelhafez, Brian Baker, András Gyenis, Pranav Mundada, Andrew A. Houck, David Schuster, and Jens Koch
Phys. Rev. A 101, 022321 – Published 18 February 2020

Abstract

We employ quantum optimal control theory to realize quantum gates for two protected superconducting circuits: the heavy-fluxonium qubit and the 0-π qubit. Utilizing automatic differentiation facilitates the simultaneous inclusion of multiple optimization targets, allowing one to obtain high-fidelity gates with realistic pulse shapes. For both qubits, disjoint support of low-lying wave functions prevents direct population transfer between the computational-basis states. Instead, optimal control favors dynamics involving higher-lying levels, effectively lifting the protection for a fraction of the gate duration. For the 0-π qubit, offset-charge dependence of matrix elements among higher levels poses an additional challenge for gate protocols. To mitigate this issue, we randomize the offset charge during the optimization process, steering the system towards pulse shapes insensitive to charge variations. Closed-system fidelities obtained are 99% or higher and show slight reductions in open-system simulations.

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  • Received 28 August 2019
  • Accepted 30 January 2020

DOI:https://doi.org/10.1103/PhysRevA.101.022321

©2020 American Physical Society

Physics Subject Headings (PhySH)

Quantum Information, Science & Technology

Authors & Affiliations

Mohamed Abdelhafez1, Brian Baker2, András Gyenis3, Pranav Mundada3, Andrew A. Houck3, David Schuster1, and Jens Koch2

  • 1The James Franck Institute and Department of Physics, University of Chicago, Chicago, Illinois 60637, USA
  • 2Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA
  • 3Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA

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Issue

Vol. 101, Iss. 2 — February 2020

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