Electronic structure with direct diagonalization on a D-Wave quantum annealer

TL;DR

This paper demonstrates solving molecular electronic structure problems using a quantum annealer with a novel matrix-based eigensolver algorithm, enabling the calculation of ground and excited states on near-term hardware.

Contribution

It introduces a general Quantum Annealer Eigensolver (QAE) algorithm tailored for D-Wave hardware, optimizing resource use and enabling electronic structure calculations.

Findings

Successfully computed ground and excited states of small molecules.

Demonstrated efficient use of qubits with power-of-two encoding.

Showed potential for integration with existing quantum chemistry software.

Abstract

Quantum chemistry is regarded to be one of the first disciplines that will be revolutionized by quantum computing. Although universal quantum computers of practical scale may be years away, various approaches are currently being pursued to solve quantum chemistry problems on near-term gate-based quantum computers and quantum annealers by developing the appropriate algorithm and software base. This work implements the general Quantum Annealer Eigensolver (QAE) algorithm to solve the molecular electronic Hamiltonian eigenvalue-eigenvector problem on a D-Wave 2000Q quantum annealer. The approach is based on the matrix formulation, efficiently uses qubit resources based on a power-of-two encoding scheme and is hardware-dominant relying on only one classically optimized parameter. We demonstrate the use of D-Wave hardware for obtaining ground and electronically excited states across a variety of small molecular systems. This approach can be adapted for use by a vast majority of electronic structure methods currently implemented in conventional quantum-chemical packages. The results of this work will encourage further development of software such as qbsolv which has promising applications in emerging quantum information processing hardware and is able to address large and complex optimization problems intractable for classical computers.