Quantum Enhanced Pauli Propagation

TL;DR

The paper introduces QuEPP, a hybrid quantum-classical algorithm that enhances the accuracy of observable estimation on noisy quantum devices without requiring noise characterization, applicable to arbitrary circuits, and demonstrated on IBM hardware.

Contribution

It presents QuEPP, a novel method combining Clifford perturbation theory with quantum expectation values to correct noise bias in quantum circuit simulations.

Findings

Demonstrated on IBM hardware with up to 49 qubits and depth 80.

Achieved consistent improvements over classical CPT and unmitigated results.

Provides a scalable, model-free approach for near-term quantum computing.

Abstract

Accurately estimating observables on noisy quantum devices remains a central challenge for near-term quantum algorithms. While quantum error mitigation techniques can reduce noise-induced bias, they often rely on unverifiable assumptions about the circuit noise, and cannot guarantee the magnitude of residual bias error. Here, rather than using classical resources to mitigate a noisy quantum circuit execution, we propose a hybrid algorithm that uses quantum resources to improve the accuracy of approximate classical Pauli-path simulation. Our protocol, Quantum Enhanced Pauli Propagation (QuEPP), uses Clifford perturbation theory (CPT) to construct a classically simulable ensemble of Clifford circuits from the low-order terms in CPT, which directly provide the approximate classical Pauli-path simulation of the target circuit. Noisy quantum expectation values of this ensemble are then used to infer a global rescaling factor that corrects quantum execution of the target circuit, providing higher-order contributions absent from the truncated low-order classical simulation. This approach requires no noise characterization, applies to arbitrary circuits, and provides a provable route to asymptotically unbiased estimates. Using IBM Heron hardware, we demonstrate QuEPP on 2D random mirror circuits of up to 49 qubits and circuit depth 80, as well as Trotterized Hamiltonian evolution, showing consistent improvements beyond classical CPT and unmitigated quantum results. QuEPP offers a simple, scalable, and model-free framework for enabling accurate quantum computation in the pre-fault-tolerant era.