Tilly, Jules L.;
(2022)
Methods for variational computation of molecular properties on near term quantum computers.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
In this thesis we explore the near term applications of quantum computing to Quantum Chemistry problems, with a focus on electronic structure calculations. We begin by discussing the core subroutine of near-term quantum computing methods: the variational quantum eigensolver (VQE). By drawing upon the literature, we discuss the relevance of the method in computing electronic structure properties, compare it to alternative conventional or quantum methods and outline best practices. We then discuss the key limitations of this method, namely: the exploding number of measurements required, showing that parallelisation will be relevant for VQE to compete with conventional methods; the barren plateau problem; and the management of errors through error mitigation - we present a light touch error mitigation technique which is used to improve the results of experiments presented later in the thesis. From this point, we propose three methods for near term applications of quantum computing, with a focus on limiting the requirements on quantum resources. The first two methods concern the computation of ground state energy. We adapt the conventional methods of complete active space self consistent field (CASSCF) and energy-weighted density matrix embedding theory (EwDMET) by integrating a VQE subroutine to compute the electronic wavefunctions from which reduced density matrices are sampled. These method allow recovering additional electron correlation energy for a given number of qubits and are tested on quantum devices. The last method is focused on computing excited electronic states and uses techniques inspired from the generative adversarial machine learning literature. It is a fully variational method, which is shown to work on current quantum devices.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Methods for variational computation of molecular properties on near term quantum computers |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10162163 |
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