PRX Quantum (Nov 2024)

High-Fidelity Two-Qubit Gates between Fluxonium Qubits with a Resonator Coupler

  • Emma L. Rosenfeld,
  • Connor T. Hann,
  • David I. Schuster,
  • Matthew H. Matheny,
  • Aashish A. Clerk

DOI
https://doi.org/10.1103/PRXQuantum.5.040317
Journal volume & issue
Vol. 5, no. 4
p. 040317

Abstract

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We take a bottom-up first-principles approach to designing a two-qubit gate between fluxonium qubits for minimal error, speed, and control simplicity. Our proposed architecture consists of two fluxoniums coupled via a resonator. The use of a simple linear coupler has many practical benefits, including the possibility of material optimization for suppressing loss, reducing fabrication complexity, and increasing yield by circumventing the need for Josephson junctions. Crucially, a resonator-as-coupler approach also suggests a clear path to increased connectivity between fluxonium qubits, by reducing capacitive loading when the coupler has a high impedance. After performing analytic and numerical analyses of the circuit Hamiltonian and gate dynamics, we tune circuit parameters to destructively interfere sources of coherent error, revealing an efficient fourth-order scaling of coherent error with gate duration. For component properties from the literature, we predict an open-system average controlled-Z (cz) gate infidelity of 1.86×10^{−4} in 70 ns.