Variational Quantum Eigensolvers for Molecular Ground-State Estimation: A Benchmark on Noisy Intermediate-Scale Quantum Hardware

Abstract

The variational quantum eigensolver (VQE) is among the most promising near-term algorithms for estimating molecular ground-state energies on noisy intermediate-scale quantum (NISQ) devices. In this work, we benchmark a hardware-efficient VQE ansatz against a chemistry-inspired unitary coupled-cluster singles and doubles (UCCSD) ansatz for a set of small molecular systems, including hydrogen (H2), lithium hydride (LiH), and beryllium hydride (BeH2). Simulations were performed under realistic noise models calibrated to superconducting qubit hardware, incorporating gate infidelity, T1/T2 decoherence, and readout error. We find that the hardware-efficient ansatz converges faster in gate count but exhibits a systematically higher variance in energy estimates due to barren plateau effects at larger qubit counts, while UCCSD offers better chemical accuracy at the cost of significantly deeper circuits. We further evaluate three error-mitigation strategies -- zero-noise extrapolation, readout-error mitigation, and symmetry verification -- and show that a combination of readout mitigation and zero-noise extrapolation recovers chemical accuracy for H2 and LiH on simulated 7-qubit and 12-qubit devices respectively. Our results offer practical guidance for ansatz and mitigation strategy selection when deploying VQE workloads on current-generation quantum hardware.

Keywords

variational quantum eigensolverquantum chemistryNISQerror mitigationVQE

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