Energy Is Not Enough: Leakage-Aware Ansatz Criterion for Variational Quantum Eigensolvers

Quantum Physics arXiv:2609.13521 (quant-ph) [Submitted on 11 Sep 2026] Title:Energy Is Not Enough: Leakage-Aware Ansatz Criterion for Variational Quantum Eigensolvers Authors:Yuan-Chieh Chen View a PDF of the paper titled Energy Is Not Enough: Leakage-Aware Ansatz Criterion for Variational Quantum Eigensolvers, by Yuan-Chieh Chen View PDF HTML (experimental) Abstract:In molecular variational quantum eigensolver (VQE) calculations for a fixed electron-number sector, the projected-sector energy alone does not certify that a prepared state is physically valid. We show that a state can have zero projected-sector error while almost all of its probability mass lies outside the target particle-number sector. We therefore evaluate ansatz families using three quantities: projected-sector error, leakage outside the physical sector and parameter count. Our noiseless experiments show that particle-preserving UCC-style families eliminate leakage induced by ansatze, but do not guarantee ground-state accuracy. In the parameter-budget comparison experiments, the one-shot ranking rules select identical generator sequences and yield identical errors. The adaptive hybrid procedure achieves lower mean projected-sector errors at selected budgets. Using established Kraus invariant-subspace criteria, we also express channel-induced leakage through a positive operator and discuss global and local depolarizing noise analytically. This gives a practical diagnostic framework for comparing ansatze beyond energy alone. Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2609.13521 [quant-ph] (or arXiv:2609.13521v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2609.13521 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Yuan-Chieh Chen [view email] [v1] Fri, 11 Sep 2026 20:44:06 UTC (96 KB) Full-text links: Access Paper: View a PDF of the paper titled Energy Is Not Enough: Leakage-Aware Ansatz Criterion for Variational Quantum Eigensolvers, by Yuan-Chieh ChenView PDFHTML (experimental)TeX Source view license Current browse context: quant-ph new | recent | 2026-09 References & Citations INSPIRE HEP NASA ADSGoogle Scholar Semantic Scholar export BibTeX citation Loading... BibTeX formatted citation × loading... Data provided by: Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Code, Data and Media Associated with this Article alphaXiv Toggle alphaXiv (What is alphaXiv?) Links to Code Toggle CatalyzeX Code Finder for Papers (What is CatalyzeX?) DagsHub Toggle DagsHub (What is DagsHub?) GotitPub Toggle Gotit.pub (What is GotitPub?) Huggingface Toggle Hugging Face (What is Huggingface?) ScienceCast Toggle ScienceCast (What is ScienceCast?) Demos Demos Replicate Toggle Replicate (What is Replicate?) Spaces Toggle Hugging Face Spaces (What is Spaces?) Spaces Toggle TXYZ.AI (What is TXYZ.AI?) Related Papers Recommenders and Search Tools Link to Influence Flower Influence Flower (What are Influence Flowers?) Core recommender toggle CORE Recommender (What is CORE?) Author Venue Institution Topic About arXivLabs arXivLabs: experimental projects with community collaborators arXivLabs is a framework that allows collaborators to develop and share new arXiv features directly on our website. Both individuals and organizations that work with arXivLabs have embraced and accepted our values of openness, community, excellence, and user data privacy. arXiv is committed to these values and only works with partners that adhere to them. Have an idea for a project that will add value for arXiv's community? Learn more about arXivLabs. Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)