Physical Review Research (Dec 2022)

Circuit connectivity boosts by quantum-classical-quantum interfaces

  • Roeland Wiersema,
  • Leonardo Guerini,
  • Juan Felipe Carrasquilla,
  • Leandro Aolita

DOI
https://doi.org/10.1103/PhysRevResearch.4.043221
Journal volume & issue
Vol. 4, no. 4
p. 043221

Abstract

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High-connectivity circuits are a major roadblock for current quantum hardware. We propose a hybrid classical-quantum algorithm to simulate such circuits without swap-gate ladders. As the main technical tool, we introduce quantum-classical-quantum interfaces. These replace an experimentally problematic gate (e.g., a long-range one) with single-qubit random measurements followed by state preparations sampled according to a classical quasiprobability simulation of the noiseless gate. Each interface introduces a multiplicative statistical overhead which, remarkably, is independent of the on-chip qubit distance. Hence, by applying interfaces to the longest-range gates in a target circuit, significant reductions in circuit depth and gate infidelity can be attained. We numerically show the efficacy of our method for a Bell-state circuit for two increasingly distant qubits and a variational ground-state solver for the transverse-field Ising model on a ring. Our findings provide a versatile toolbox for error-mitigation and circuit boosts tailored for noisy, intermediate-scale quantum computation.