Cited by 1,082Quantum Computing Algorithms and ArchitectureQuantum many-body systemsQuantum Information and Cryptography

The DOI matches its Crossref record; 53 of the 53 references it cites were found in a registry or an index; none of the 30 sources its claims cite is checked for support yet.

The power of quantum neural networks

Open access
Abbas, Amira, Sutter, David, Zoufal, Christa, Lucchi, Aurelien, Figalli, Alessio, Woerner, Stefan·2021·Nature Computational Science

Abstract

It is unknown whether near-term quantum computers are advantageous for machine learning tasks. In this work we address this question by trying to understand how powerful and trainable quantum machine learning models are in relation to popular classical neural networks. We propose the effective dimension-a measure that captures these qualities-and prove that it can be used to assess any statistical model's ability to generalize on new data. Crucially, the effective dimension is a data-dependent measure that depends on the Fisher information, which allows us to gauge the ability of a model to train. We demonstrate numerically that a class of quantum neural networks is able to achieve a considerably better effective dimension than comparable feedforward networks and train faster, suggesting an advantage for quantum machine learning, which we verify on real quantum hardware.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

The paper uses information geometry and the effective dimension to argue that well-designed quantum neural networks can achieve higher capacity and faster training than comparable classical feedforward networks. It links the Fisher information spectrum to barren plateaus and verifies a training advantage on the ibmq montreal 27-qubit device.

Key findings

  • The quantum neural network consistently achieves the highest effective dimension over the finite-data ranges considered, followed by the easy quantum model and then the classical feedforward network; with \(s_{\text{in}}=4\), \(s_{\text{out}}=2\), and \(d=40\), the quantum model’s Fisher information spectrum is more uniform and lacks the classical model’s few very large eigenvalues.
  • In training on the first two classes of the Iris dataset with \(d=8\), 100 iterations, ADAM with initial learning rate \(0.1\), and 100 trials, the quantum neural network reaches the lowest average training loss: \(23.14\%\), versus \(43.05\%\) for the easy quantum model and \(37.90\%\) for the classical network; average Fisher-Rao norms are \(117.84\), \(104.89\), and \(46.45\), respectively.
  • The Fisher information spectrum connects to barren plateaus: the easy, classically simulable feature map becomes more “barren plateau-like” as qubit number increases, while the harder higher-order feature map shows resilience, with eigenvalues not concentrating near zero as system size grows.
  • On real hardware, the quantum neural network is trained on the ibmq montreal 27-qubit device using 4 qubits with linear connectivity; training stabilizes after roughly 33 iterations, and the paper reports performance even better than simulated results.

Methods

  • The paper defines neural networks as statistical models, uses the Fisher information matrix and effective dimension as capacity measures, proves a novel generalisation bound based on effective dimension (Theorem 3.2), and extends it to models without full-rank Fisher information via discretisation.
  • It compares a quantum neural network using a depth-2 higher-order feature map and parameterised RY/CNOT variational form against classical feedforward networks and an “easy” quantum model with classically simulable angle encoding, matching models by number of trainable parameters \(d\), input size \(s_{\text{in}}\), and output size \(s_{\text{out}}\), with \(d \le 100\), \(s_{\text{in}} \in \{4,6,8,10\}\), and \(s_{\text{out}}=2\).
  • Numerical experiments sample 100 parameter sets to estimate Fisher information spectra, train on the first two Iris classes with \(d=8\), 100 iterations, ADAM, learning rate \(0.1\), and 100 trials, and run one hardware training on ibmq montreal with 4 qubits and linear entanglement.

Limitations

  • Stated: the hardware experiment is run only once due to limited hardware availability, and the authors note that analysis of hardware noise and spread over differently sampled initial parameters would make the results more robust.
  • Stated: future work is needed on noise-induced barren plateaus, generalisation on multiple datasets, and larger models; the hard feature map’s classical hardness is conjectured rather than proven.
  • Evident: comparisons are limited to specific feedforward topologies, a small Iris subset, and \(d \le 100\); effective-dimension estimates rely on Monte Carlo sampling and the paper notes that higher dimensions likely require more samples.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1038/s43588-021-00084-1

Cites

53 of 53 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

28 Own interpretation · 23 Own result · 22 Not checked yet · 9 No basis given · 3 Own method

Verify all 30 references — free account

Show all 43 claims

  • It may state two separate claims as one. 27
  • Probably not a substantial claim. 18
42 of 42
  • The authors state this as an assumption.

    The statistical model satisfies the regularity assumption (4).

    “We assume the following regularity assumption on the model M Θ := { p ( · , · ; θ ) : θ ∈ Θ } :”
  • The paper relies on this without support.

    The feature map used in the quantum neural network is hard to simulate classically.

    “The feature map in the quantum neural network is conjectured to be hard to simulate classically”
    “The quantum neural network's encoding scheme is conjectured to be difficult.”
  • The paper relies on this without support.

    The capacity of quantum neural networks is not well explored, and no such Fisher information analysis has been done for them.

    “In stark contrast to classical models, understanding the capacity of quantum neural networks is not well explored.”
    “For quantum neural networks, no such analysis has been done.”
  • The authors state this as an assumption.

    The loss function in Theorem 3.2 is bounded.

    “the assumption that the loss function in Theorem 3.2 has to be bounded.”
  • The paper relies on this without support.

    The relative entropy is α-Hölder continuous in its first argument for α∈(0,1) and log-Lipschitz continuous in its first argument.

    “We further note that the relative entropy is α -H¨ older continuous in the first argument for α ∈ (0 , 1). In fact, the relative entropy is even log-Lipschitz continuous in the first argument”
  • The paper relies on this without support.

    In practical applications, the Fisher matrix is evaluated at finitely many points.

    “Our approach to this general problem is based on the idea that, in practical applications, the Fisher matrix is evaluated at finitely many points, so it makes sense to approximate a statistical model with a discretised one where the corresponding Fisher information matrix is piecewise constant.”
6 of 6

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2 of 2

Citations

Cites

Show all 39 references

Research works printed but not linked: 13

  1. Goodfellow, I., Bengio, Y. & Courville, A. Deep Learning (MIT Press, 2016); http://www.deeplearningbook.org
  2. Farhi, E. & Neven, H. Classification with quantum neural networks on near term processors. Quant. Rev. Lett. 1, 2 (2020).
  3. Sontag, E. D Neural Networks and Machine Learning 69–95 (Springer, 1998).
  4. Neyshabur, B., Bhojanapalli, S., McAllester, D. & Srebro, N. Exploring generalization in deep learning. In Advances in Neural Information Processing Systems 30, 5947–5956 (NIPS, 2017).
  5. Kunstner, F., Hennig, P. & Balles, L. Limitations of the empirical Fisher approximation for natural gradient descent. In Advances in Neural Information Processing Systems 32 4156–4167 (NIPS, 2019); http://papers.nips.cc/paper/limitations-of-fisher-approximation
  6. Karakida, R., Akaho, S. & Amari, S.-I. Universal statistics of Fisher information in deep neural networks: mean field approach. In Proc. Machine Learning Research Vol. 89, 1032–1041 (PMLR, 2019); http://proceedings.mlr.press/v89/karakida19a.html
  7. Liang, T., Poggio, T., Rakhlin, A. & Stokes, J. Fisher–Rao metric, geometry, and complexity of neural networks. In Proc. Machine Learning Research Vol. 89, 888–896 (PMLR, 2019); http://proceedings.mlr.press/v89/liang19a.html
  8. Neyshabur, B., Salakhutdinov, R. R. & Srebro, N. Path-SGD: path-normalized optimization in deep neural networks. In Advances in Neural Information Processing Systems 28, 2422–2430 (NIPS, 2015).
  9. Neyshabur, B., Tomioka, R. & Srebro, N. Norm-based capacity control in neural networks. In Proc. Machine Learning Research Vol. 40, 1376–1401 (PMLR, 2015); http://proceedings.mlr.press/v40/Neyshabur15.html
  10. Bartlett, P. L., Foster, D. J. & Telgarsky, M. J. Spectrally-normalized margin bounds for neural networks. In Advances in Neural Information Processing Systems 30, 6240–6249 (NIPS, 2017); http://papers.nips.cc/paper/7204-spectrally-normalized
  11. Rissanen, J. J. Fisher information and stochastic complexity. IEEE Trans. Inf. Theory 42, 40–47 (1996). · DOI · Paper page
  12. Marrero, C. O., Kieferová, M. & Wiebe, N. Entanglement induced barren plateaus. Preprint at https://arxiv.org/abs/2010.15968 (2020). · arXiv
  13. Virmaux, A. & Scaman, K. Lipschitz regularity of deep neural networks: analysis and efficient estimation. In Advances in Neural Information Processing Systems 31, 3835–3844 (NIPS, 2018); http://papers.nips.cc/paper/lipschitz-regularity-of-deep-neural-networks

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Metadata

Authors
Abbas, A., Sutter, D., Zoufal, C., Lucchi, A., Figalli, A., & Woerner, S.
Affiliations
  • IBM Research - Zurich (CH)
  • ETH Zurich (CH)
Corresponding author
Woerner, Stefan
Venue
Nature Computational Science
Published
2021-06-24
Volume
1
Issue
6
Pages
403-409
ISSN
2662-8457 (ISSN-L)
OpenAlex
W3097610849
Cited by
1,082
References
39
Citations by year
2026: 266 · 2025: 266 · 2024: 216 · 2023: 178 · 2022: 87 · 2021: 69
FWCI
48.59
Type
journal article
Language
en
Open access
Locations
  • Nature Computational Science (publishedVersion)
  • PubMed (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • arXiv (Cornell University)
Funders
International Business Machines Corporation
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Computing Algorithms and Architecture
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum many-body systems
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Information and Cryptography
Keywords
quantum neural networks, quantum machine learning, effective dimension, Fisher information, generalization, model capacity, training speed, quantum advantage, feedforward neural networks, quantum computing hardware

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