Using Quantum Annealers to Calculate Ground State Properties of Molecules

TL;DR

This paper explores the use of quantum annealers for calculating molecular ground state properties, comparing two methods and assessing their effectiveness and resource needs, highlighting current limitations compared to classical algorithms.

Contribution

It introduces and compares two methods for mapping molecular Hamiltonians to Ising models on quantum annealers for small molecules.

Findings

Both methods accurately predict ground state properties of small molecules.

Quantum annealers currently require more resources than classical algorithms.

Scaling remains a challenge for applying quantum annealers to larger molecules.

Abstract

Quantum annealers are an alternative approach to quantum computing which make use of the adiabatic theorem to efficiently find the ground state of a physically realizable Hamiltonian. Such devices are currently commercially available and have been successfully applied to several combinatorial and discrete optimization problems. However, the application of quantum annealers to problems in chemistry remains a relatively sparse area of research due to the difficulty in mapping molecular systems to the Ising model Hamiltonian. In this paper we review two different methods for finding the ground state of molecular Hamiltonians using Ising model-based quantum annealers. In addition, we compare the relative effectiveness of each method by calculating the binding energies, bond lengths, and bond angles of the H+3and H2O molecules and mapping their potential energy curves. We also assess the resource requirements of each method by determining the number of qubits and computation time required to simulate each molecule using various parameter values. While each of these methods is capable of accurately predicting the ground state properties of small molecules, we find that they are still outperformed by modern classical algorithms and that the scaling of the resource requirements remains a challenge.