Error Sensitivity to Environmental Noise in Quantum Circuits for Chemical State Preparation

TL;DR

This paper investigates how environmental noise affects quantum chemistry state preparation in quantum circuits, revealing encoding and noise-type dependencies that inform future quantum simulation accuracy.

Contribution

It provides a comparative analysis of noise effects on different encodings and noise types in quantum chemistry simulations, guiding hardware and algorithm choices.

Findings

Jordan-Wigner encoding yields smaller errors under noise.

Pure-dephasing noise causes less error than relaxation noise.

Error trends depend on molecular parameters and noise characteristics.

Abstract

Calculating molecular energies is likely to be one of the first useful applications to achieve quantum supremacy, performing faster on a quantum than a classical computer. However, if future quantum devices are to produce accurate calculations, errors due to environmental noise and algorithmic approximations need to be characterized and reduced. In this study, we use the high performance qHiPSTER software to investigate the effects of environmental noise on the preparation of quantum chemistry states. We simulated eighteen 16-qubit quantum circuits under environmental noise, each corresponding to a unitary coupled cluster state preparation of a different molecule or molecular configuration. Additionally, we analyze the nature of simple gate errors in noise-free circuits of up to 40 qubits. We find that the Jordan-Wigner (JW) encoding produces consistently smaller errors under a noisy environment as compared to the Bravyi-Kitaev (BK) encoding. For the JW encoding, pure-dephasing noise is shown to produce substantially smaller errors than pure relaxation noise of the same magnitude. We report error trends in both molecular energy and electron particle number within a unitary coupled cluster state preparation scheme, against changes in nuclear charge, bond length, number of electrons, noise types, and noise magnitude. These trends may prove to be useful in making algorithmic and hardware-related choices for quantum simulation of molecular energies.