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Automated Variational Ansatz Design
Thesis (PhD)--Stellenbosch University, 2026.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1867613810240520192 |
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| access_status_str | Open Access |
| author | Lourens, Matthys Johannes |
| author2 | Petruccione, Francesco |
| author_browse | Lourens, Matthys Johannes Petruccione, Francesco |
| author_facet | Petruccione, Francesco Lourens, Matthys Johannes |
| author_sort | Lourens, Matthys Johannes |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2026. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/136282 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:42:03.173Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/136282 Automated Variational Ansatz Design Lourens, Matthys Johannes Petruccione, Francesco Sinayskiy, Ilya Stellenbosch University. Faculty of Science. Dept. of Physics. Thesis (PhD)--Stellenbosch University, 2026. Lourens, M. J. 2026. Automated Variational Ansatz Design. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/332e5e78-1815-4bb9-a9bb-17bcde76f540 We develop a systematic approach to ansatz design for quantum many-body problems. The approach is based on an abstract hypergraph language that compactly encodes modular, size-scalable and hierarchically composable wavefunction structures. With this language, evolutionary search can be carried out on few-body instances, yet the resulting wavefunctions extrapolate to arbitrary system size without modification. This enables efficient fitness evaluation and the capture of robust wavefunction structures. Applied to ground-state problems, the method autonomously rediscovers a mean-field description and extends it to incorporate correlations, producing simple, interpretable wavefunctions that remain analytically tractable. For both the Lipkin-Meshkov-Glick model and the transverse-field I sing model, the search converges on the same compact, twoparameter ansatz. Owing to its structure, we obtain closed-form expressions for energies and correlation functions. These results far surpass mean-field theory on finite systems and become exact or near-exact in the thermodynamic limit. The same framework also generates a quantum phase-recognition ansatz that outperforms a commonly used architecture while reducing the number of required variational parameters by two orders of magnitude. Finally, by training only on small-circuit examples, the method automatically produces general 𝑁-qubit realisations of standard quantum algorithms, namely the Deutsch-Jozsa algorithm, the quantum Fourier transform, and Grover’s search. Taken together, our approach provides a concrete pathway towards a general, systematic theory of variational ansatz design. Doctoral 2026-04-30T13:53:58Z 2026-04-30T13:53:58Z 2026-03 Thesis https://scholar.sun.ac.za/handle/10019.1/136282 en Stellenbosch University 127 pages application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Lourens, Matthys Johannes Automated Variational Ansatz Design |
| title | Automated Variational Ansatz Design |
| title_full | Automated Variational Ansatz Design |
| title_fullStr | Automated Variational Ansatz Design |
| title_full_unstemmed | Automated Variational Ansatz Design |
| title_short | Automated Variational Ansatz Design |
| title_sort | automated variational ansatz design |
| url | https://scholar.sun.ac.za/handle/10019.1/136282 |
| work_keys_str_mv | AT lourensmatthysjohannes automatedvariationalansatzdesign |