Thermal coupled cluster theory for SU(2) systems

TL;DR

This paper develops a thermal coupled cluster theory tailored for SU(2) spin systems, extending finite-temperature quantum many-body methods beyond fermionic and bosonic cases, and demonstrates its accuracy on benchmark models.

Contribution

It introduces a thermofield-inspired thermal CC formulation specifically for SU(2) systems, filling a gap in finite-temperature many-body theory for spin degrees of freedom.

Findings

Accurately describes finite-temperature phase diagrams of SU(2) systems.

Successfully applied to Lipkin-Meshkov-Glick and transverse field Ising models.

Shows comparable or improved accuracy over existing methods.

Abstract

Coupled cluster (CC) has established itself as a powerful theory to study correlated quantum many-body systems. Finite-temperature generalizations of CC theory have attracted considerable interest and have been shown to work as nicely as the ground-state theory. However, most of these recent developments address only fermionic or bosonic systems. The distinct structure of the $su(2)$ algebra requires the development of a similar thermal CC theory for spin degrees of freedom. In this paper, we provide a formulation of our thermofield-inspired thermal CC for SU(2) systems. We apply the thermal CC to the Lipkin-Meshkov-Glick system as well as the one-dimensional transverse field Ising model as benchmark applications to highlight the accuracy of thermal CC in the study of finite-temperature phase diagrams in SU(2) systems.