Circuit connectivity boosts by quantum-classical-quantum interfaces

TL;DR

This paper introduces quantum-classical-quantum interfaces to enhance circuit connectivity in quantum hardware, reducing depth and infidelity without swap gates, and demonstrating effectiveness on Bell-state and Ising model circuits.

Contribution

The paper presents a novel hybrid algorithm using quantum-classical-quantum interfaces to simulate high-connectivity circuits efficiently, avoiding swap-gate ladders and improving performance.

Findings

Significant reduction in circuit depth and infidelity achieved.

Effective for long-range gates in quantum circuits.

Numerical validation on Bell-state and Ising model circuits.

Abstract

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 main technical tool, we introduce quantum-classical-quantum interfaces. These replace an experimentally problematic gate (e.g. a long-range one) by single-qubit random measurements followed by state-preparations sampled according to a classical quasi-probability simulation of the noiseless gate. Each interface introduces a multiplicative statistical overhead which is remarkably 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.