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On measurement-dependent variance in quantum neural networks

arXiv Quantum Physics
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⚡ Quantum Brief
Russian researchers Kardashin and Antipin reveal that partial qubit measurements in quantum neural networks increase prediction variance in regression tasks, challenging assumptions about measurement strategies in quantum machine learning. The study focuses on variational quantum circuits—particularly quantum convolutional neural networks (QCNNs)—where only subsets of qubits are measured, showing this approach degrades performance compared to full-state measurements. The core issue stems from the reduced number of distinct eigenvalues in observables after partial measurements, which directly correlates with higher variance in label predictions for regression problems. Their analysis demonstrates that local observable measurements, common in QML architectures, inherently limit the information available for training, undermining the precision of quantum-enhanced learning models. Published January 2026, the findings urge reevaluation of measurement protocols in hybrid quantum-classical algorithms to mitigate variance and improve reliability in practical QML applications.
On measurement-dependent variance in quantum neural networks

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Quantum Physics arXiv:2601.08029 (quant-ph) [Submitted on 12 Jan 2026] Title:On measurement-dependent variance in quantum neural networks Authors:Andrey Kardashin, Konstantin Antipin View a PDF of the paper titled On measurement-dependent variance in quantum neural networks, by Andrey Kardashin and 1 other authors View PDF HTML (experimental) Abstract:Variational quantum circuits have become a widely used tool for performing quantum machine learning (QML) tasks on labeled quantum states. In some specific tasks or for specific variational ansätze, one may perform measurements on a restricted part of the overall input state. This is the case for, e.g., quantum convolutional neural networks (QCNNs), where after each layer of the circuit a subset of qubits of the processed state is measured or traced out, and at the end of the network one typically measures a local observable. In this work, we demonstrate that measuring observables with restricted support results in larger label prediction variance in regression QML tasks. We show that the reason for this is, essentially, the number of distinct eigenvalues of the observable one measures after the application of a variational circuit. Comments: Subjects: Quantum Physics (quant-ph) Cite as: arXiv:2601.08029 [quant-ph] (or arXiv:2601.08029v1 [quant-ph] for this version) https://doi.org/10.48550/arXiv.2601.08029 Focus to learn more arXiv-issued DOI via DataCite (pending registration) Submission history From: Andrey Kardashin [view email] [v1] Mon, 12 Jan 2026 22:01:32 UTC (2,283 KB) Full-text links: Access Paper: View a PDF of the paper titled On measurement-dependent variance in quantum neural networks, by Andrey Kardashin and 1 other authorsView PDFHTML (experimental)TeX Source view license Current browse context: quant-ph new | recent | 2026-01 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?) Links to Code Toggle Papers with Code (What is Papers with Code?) 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?)

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quantum-hardware
quantum-machine-learning

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Source: arXiv Quantum Physics