Optimized Quantum Phase Estimation for Simulating Electronic States in Various Energy Regimes

TL;DR

This paper introduces QPESIM, a new classical simulation tool for quantum phase estimation, enabling efficient simulation of electronic states in molecules like H₂O with reduced errors for larger active spaces.

Contribution

The paper presents QPESIM, a versatile and resource-efficient classical simulator for quantum phase estimation applied to electronic state calculations.

Findings

QPESIM effectively simulates ground and core-level states of H₂O.

Increasing active space size improves energy calculation accuracy.

Simulations with 15 active orbitals significantly reduce errors in core-level energies.

Abstract

While quantum algorithms for simulation exhibit better asymptotic scaling than their classical counterparts, they currently cannot be implemented on real-world devices. Instead, chemists and computer scientists rely on costly classical simulations of these quantum algorithms. In particular, the quantum phase estimation (QPE) algorithm is among several approaches that have attracted much attention in recent years for its genuine quantum character. However, it is memory-intensive to simulate and intractable for moderate system sizes. This paper discusses the performance and applicability of QPESIM, a new simulation of the QPE algorithm designed to take advantage of modest computational resources. In particular, we demonstrate the versatility of QPESIM in simulating various electronic states by examining the ground and core-level states of H$_2$O. For these states, we also discuss the effect of the active-space size on the quality of the calculated energies. For the high-energy core-level states, we demonstrate that new QPE simulations for active spaces defined by 15 active orbitals significantly reduce the errors in core-level excitation energies compared to earlier QPE simulations using smaller active spaces.