Chemically-Accurate Prediction of the Ionisation Potential of Helium Using a Quantum Processor

Abstract

Quantum computers have the potential to revolutionise our understanding of the microscopic behaviour of materials and chemical processes by enabling high-accuracy electronic structure calculations to scale more efficiently than is possible using classical computers. Current quantum computing hardware devices suffer from the dual challenges of noise and cost, which raises the question of what practical value these devices might offer before full fault tolerance is achieved and economies of scale enable cheaper access. Here we examine the practical value of noisy quantum computers as tools for high-accuracy electronic structure, by using a Quantinuum ion-trap quantum computer to predict the ionisation potential of helium. By combining a series of techniques suited for use with current hardware including qubit-efficient encoding coupled with chemical insight, low-cost variational optimisation with hardware-adapted quantum circuits, and moments-based corrections, we obtain an ionisation potential of 24.5536 (+0.0011, -0.0005) eV, which agrees with the experimentally measured value to within true chemical accuracy, and with high statistical confidence. The methods employed here can be generalised to predict other properties and expand our understanding of the value that might be provided by near-term quantum computers.