Towards Quantum Advantage in Chemistry

TL;DR

This paper demonstrates a quantum algorithm executed on classical hardware to simulate complex molecules, showing quantum advantage is achievable with hundreds of logical qubits, and clarifies resource needs for future quantum computers.

Contribution

It executes the iterative qubit coupled-cluster algorithm at unprecedented scale, providing benchmarks and resource estimates for quantum advantage in chemistry.

Findings

iQCC achieves lowest mean absolute error (0.05 eV) in excited state energies

Simulations of organometallic complexes require hundreds of logical qubits

Quantum advantage in chemistry may emerge around 200 logical qubits

Abstract

Molecular simulations are widely regarded as leading candidates to demonstrate quantum advantage--defined as the point at which quantum methods surpass classical approaches in either accuracy or scale. Yet the qubit counts and error rates required to realize such an advantage remain uncertain; resource estimates for ground-state electronic structure span orders of magnitude, and no quantum-native method has been validated at a commercially relevant scale. Here we address this uncertainty by executing the iterative qubit coupled-cluster (iQCC) algorithm, designed for fault-tolerant quantum hardware, at unprecedented scale using a quantum solver on classical processors, enabling simulations of transition organo-metallic complexes requiring hundreds of logical qubits and millions of entangling gates. Using this approach, we compute the lowest triplet excited state (T$_1$) energies of Ir(III) and Pt(II) phosphorescent organometallic compounds and show that iQCC achieves the lowest mean absolute error (0.05 eV) and highest R$^2$ (0.94) relative to experiment, outperforming leading classical methods. We find these systems remain classically tractable up to $\sim$200 logical qubits, establishing the threshold at which quantum advantage in computational chemistry may emerge and clarifying resource requirements for future quantum computers.