Improving VQE Parameter Quality on Noisy Quantum Processors with Cost-Effective Readout Error Mitigation

TL;DR

This paper demonstrates that cost-effective readout error mitigation, specifically T-REx, significantly enhances VQE accuracy on noisy quantum processors, enabling more reliable molecular energy estimations and parameter optimization.

Contribution

The study introduces T-REx, an inexpensive error mitigation technique, showing its effectiveness in improving VQE results on small quantum devices despite hardware noise.

Findings

T-REx improves VQE energy estimation accuracy by an order of magnitude.

Optimized variational parameters are more reliable benchmarks than raw hardware energies.

Even older quantum hardware benefits from error mitigation for molecular simulations.

Abstract

The inherent noise in current Noisy Intermediate-Scale Quantum (NISQ) devices presents a major obstacle to the accurate implementation of quantum algorithms such as the Variational Quantum Eigensolver (VQE) for quantum chemistry applications. This study examines the impact of error mitigation strategies on VQE performance. We show that, for small molecular systems, an older-generation 5-qubit quantum processing unit (IBMQ Belem), when combined with optimized Twirled Readout Error Extinction (T-REx), achieves ground-state energy estimations an order of magnitude more accurate than those obtained from a more advanced 156-qubit device (IBM Fez) without error mitigation. Our findings demonstrate that T-REx, a computationally inexpensive error mitigation technique, substantially improves VQE accuracy not only in energy estimation, but more importantly in optimizing the variational parameters that characterize the molecular ground state. Consequently, state-vector simulated energies suggest that the accuracy of the optimized variational parameters provides a more reliable benchmark of VQE performance than quantum hardware energy estimates alone. Our results point to the critical role of error mitigation in extending the utility of noisy quantum hardware for molecular simulations.