Reconstructing Thermal Quantum Quench Dynamics from Pure States

TL;DR

This paper presents a method to efficiently simulate thermal quantum quench dynamics on quantum computers by focusing on the most significant density matrix elements and exploiting symmetries, enabling more accurate near-term quantum simulations.

Contribution

The authors introduce a technique to reduce the complexity of simulating thermal states by selecting dominant density matrix elements and utilizing Hamiltonian symmetries.

Findings

Significant reduction in basis states needed for accurate thermal state simulation.

Method enables more precise thermal dynamics simulations on near-term quantum hardware.

Approach captures density matrix to a specified precision using weighted largest elements.

Abstract

Simulating the nonequilibrium dynamics of thermal states is a fundamental problem across scales from high energy to condensed matter physics. Quantum computers may provide a way to solve this problem efficiently. Preparing a thermal state on a quantum computer is challenging, but there exist methods to circumvent this by computing a weighted sum of time-dependent matrix elements in a convenient basis. While the number of basis states can be large, in this work we show that it can be reduced by simulating only the largest density matrix elements by weight, capturing the density matrix to a specified precision. Leveraging Hamiltonian symmetries enables further reductions. This approach paves the way to more accurate thermal-state dynamics simulations on near-term quantum hardware.