Coupled cluster method tailored with quantum computing

TL;DR

This paper introduces a hybrid quantum-classical method that corrects quantum computing results for chemical systems using coupled cluster theory, improving accuracy in potential energy calculations.

Contribution

It presents a novel approach combining quantum state tomography with coupled cluster theory to enhance quantum chemistry calculations on quantum computers.

Findings

Accurately computed potential energy curves for LiH, H2O, and N2.

Successfully estimated activation energy of a chemical reaction.

Demonstrated the method's effectiveness even when standard coupled cluster fails.

Abstract

Introducing an active space approximation is inevitable for the quantum computations of chemical systems. However, this approximation ignores the electron correlations related to non-active orbitals. Here, we propose a computational method for correcting quantum computing results using a well-established classical theory called coupled cluster theory. Our approach efficiently extracts the quantum state from a quantum device by computational basis tomography. The extracted expansion coefficients of the quantum state are embedded into the coupled cluster ansatz within the framework of the tailored coupled cluster method. We demonstrate the performance of our method by verifying the potential energy curves of LiH, H2O, and N2 with a correlation-energy correction scheme. Our method demonstrates reasonable potential energy curves even when the standard coupled cluster fails. The sufficient numbers of measurements for tomography were also investigated. Furthermore, this method successfully estimated the activation energy of the Cope rearrangement reaction of 1,5-hexadiene together with perturbative triples correction. These demonstrations suggest that our approach has the potential for practical quantum chemical calculations using quantum computers.