Fast thermal state preparation beyond native interactions

TL;DR

This paper introduces a unitary dynamics-based framework for efficiently preparing thermal states with non-native interactions in quantum simulators, applicable to both digital and analogue devices, and independent of temperature and criticality.

Contribution

It presents a novel classical control method to design quantum simulations of thermal states with non-native interactions, surpassing traditional state-vector or density-matrix approaches.

Findings

Control sequences successfully prepare thermal states for large systems.

Preparation time is independent of temperature and criticality.

Method applicable to both digital and analogue quantum devices.

Abstract

While questions on quantum simulation of ground state physics are mostly focussed on the realization of effective interactions, most work on quantum simulation of thermal physics explores the realization of dynamics towards a thermal mixed state under native interactions. Many open questions that could be answered with quantum simulations, however, involve thermal states with respect to synthetic interactions. We present a framework based solely on unitary dynamics to design quantum simulations for thermal states with respect to Hamiltonians that include non-native interactions, suitable for both present-day digital and analogue devices. By classical means, our method finds the control sequence to reach a target thermal state for system sizes well out of reach of state-vector or density-matrix control methods, even though quantum hardware is required to explicitly simulate the thermal state dynamics. With the illustrative example of the cluster Ising model that includes non-native three-body interactions, we find that required experimental resources, such as the total evolution time, are independent of temperature and criticality.