Quantum Imaginary Time Propagation algorithm for preparing thermal states

TL;DR

This paper introduces a novel quantum algorithm for preparing thermal states using imaginary time propagation, enabling accurate thermal density matrices on general quantum hardware for various Hamiltonians.

Contribution

It presents the first quantum algorithm that employs a diluted operator with ancilla qubits to simulate imaginary time evolution for thermal state preparation.

Findings

Successfully prepared thermal states of neutron systems on quantum hardware.

Demonstrated the method's reliability in computing thermal properties.

First implementation of general thermal state preparation on quantum processors.

Abstract

Calculations at finite temperatures are fundamental in different scientific fields, from nuclear physics to condensed matter. Evolution in imaginary time is a prominent classical technique for preparing thermal states of quantum systems. We propose a new quantum algorithm that prepares thermal states based on the quantum imaginary time propagation method, using a diluted operator with ancilla qubits to overcome the non-unitarity nature of the imaginary time operator. The presented method is the first that allows us to obtain the correct thermal density matrix on a general quantum processor for a generic Hamiltonian. We prove its reliability in the actual quantum hardware computing thermal properties for two and three neutron systems.