Book/Report

FZJ-2023-04617

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png The Variational Quantum Eigensolver in Quantum Chemistry with PennyLane

Symeonidou, S. (Corresponding author)

2023
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

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Please use a persistent id in citations: doi:10.34734/FZJ-2023-04617

Report No.: 4443

Abstract: This thesis explores quantum chemistry using the Variational Quantum Eigensolver (VQE), developed with the help of PennyLane’s quantum chemistry library. Our focus was on exploring molecular structures and energy landscapes. With an adaptive VQE implementation, we generated approximate multi-electron wave functions by optimizing a quantum circuit on a simulator. We started from a Hartree-Fock state and applied the UCCSD (Unitary Coupled Cluster Singles and Doubles) Ansatz to entangle electrons and lower the Hamiltonian’s expectation value. The journey began with H2, where the VQE accurately predicted its equilibrium distance and energy. We then extended our analysis to more complex molecules like LiH, BeH2, and H2O, successfully determining their equilibrium geometries and energies, which match existing literature. However, we discovered anomalies in the energy surfaces of BeH2 and H2O at larger internuclear distances, leading us to question the choice of initial states for these scenarios. In summary, this work demonstrated the VQE’s potential for accurate molecular simulations. While it excels in capturing ground states for various molecules, challenges remain for large internuclear distances. This sheds light on the evolving landscape of quantum technologies applied to understanding molecular systems.

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Contributing Institute(s):

1. Theoretische Nanoelektronik (PGI-2)
2. Theoretische Nanoelektronik (IAS-3)

Research Program(s):

1. 5221 - Advanced Solid-State Qubits and Qubit Systems (POF4-522) (POF4-522)

Appears in the scientific report 2023

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