A Quantum Computing View on Unitary Coupled Cluster Theory

TL;DR

This paper reviews the Unitary Coupled Cluster (UCC) ansatz and related methods for solving electronic structure problems on quantum computers, discussing their formulation, implementation, and open challenges.

Contribution

It provides a comprehensive overview of UCC and related ansätze, unifying various approaches and highlighting open problems in quantum computational chemistry.

Findings

Detailed discussion of UCC implementation on quantum hardware

Comparison of UCC with classical coupled cluster methods

Identification of open problems in quantum ansatz development

Abstract

We present a review of the Unitary Coupled Cluster (UCC) ansatz and related ans\"atze which are used to variationally solve the electronic structure problem on quantum computers. A brief history of coupled cluster (CC) methods is provided, followed by a broad discussion of the formulation of CC theory. This includes touching on the merits and difficulties of the method and several variants, UCC among them, in the classical context, to motivate their applications on quantum computers. In the core of the text, the UCC ansatz and its implementation on a quantum computer are discussed at length, in addition to a discussion on several derived and related ans\"atze specific to quantum computing. The review concludes with a unified perspective on the discussed ans\"atze, attempting to bring them under a common framework, as well as with a reflection upon open problems within the field.