Cited by 276Quantum Computing Algorithms and ArchitectureQuantum Information and CryptographyQuantum many-body systems

The DOI matches its Crossref record; 54 of the 54 references it cites were found in a registry or an index; 1 of the 24 sources its claims cite were checked for support.

Quantum generalisation of feedforward neural networks

Open access

Abstract

We propose a quantum generalisation of a classical neural network. The classical neurons are firstly rendered reversible by adding ancillary bits. Then they are generalised to being quantum reversible, i.e., unitary (the classical networks we generalise are called feedforward, and have step-function activation functions). The quantum network can be trained efficiently using gradient descent on a cost function to perform quantum generalisations of classical tasks. We demonstrate numerically that it can: (i) compress quantum states onto a minimal number of qubits, creating a quantum autoencoder, and (ii) discover quantum communication protocols such as teleportation. Our general recipe is theoretical and implementation-independent. The quantum neuron module can naturally be implemented photonically.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

The paper proposes a quantum generalisation of classical feedforward neural networks by making classical neurons reversible with ancillary bits and then unitary, allowing coherent processing of quantum inputs. It numerically demonstrates a quantum autoencoder and a network that discovers the teleportation protocol, and sketches a photonic implementation.

Key findings

  • The quantum network can be trained by global gradient descent on a cost function based on local Pauli expectation values, and the number of weights grows polynomially in the number of neurons.
  • As a quantum autoencoder, it compresses quantum states onto fewer qubits: for inputs \((|00\rangle+|11\rangle)/\sqrt{2}\) and \((|00\rangle-|11\rangle)/\sqrt{2}\), the cost function converged to zero, and qualitatively identical convergence was obtained for other orthogonal 2-qubit inputs and for 3 input qubits with 1 bottleneck qubit.
  • For two non-orthogonal inputs and a 1-qubit bottleneck, the cost function does not converge to zero, but training yields an approximately compressing unitary.
  • The network discovered the teleportation protocol: after training, testing on 1000 states randomly picked from the Haar measure gave a cost-function distribution with mean \(5.0371 \times 10^{-4}\) and standard deviation \(1.7802 \times 10^{-4}\), described as effectively zero.

Methods

  • Theoretical construction: classical feedforward neurons with Heaviside activation are first made reversible by adding ancillary bits, then generalised to unitary quantum neurons; classical copying is replaced by a general 2-qubit “fan-out” unitary \(U_F\).
  • Training: global gradient descent on a quantum cost function using local Pauli expectation values, with parameters \(\alpha_{j_1,\dots,j_N}\) in the unitary parametrisation; numerical simulations were run for the autoencoder and teleportation tasks.
  • Photonic implementation: a neuron module is designed using the Cerf-Adami-Kwiat protocol, encoding one qubit in polarisation and others in spatial modes, with variable beamsplitters, phase shifters, and polarisation rotators.

Limitations

  • The paper states it does not prove that convergence to zero cost, where possible, will always take a number of iterations growing polynomially in the number of neurons.
  • The paper states that classical simulation of quantum systems is generally inefficient, so efficiency claims refer to physical quantum implementation.
  • The paper states the single-photon photonic scheme does not scale well because the number of spatial modes grows exponentially in the number of qubits; it also notes that omitting ancillary qubits can sacrifice classical-mode performance.
  • Evident from the text: the demonstrations are numerical simulations, and the data availability statement says this is a theoretical paper with no experimental data beyond the described numerical simulation data.

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Integrity signals

Registry

Crossref · 10.1038/s41534-017-0032-4

Cites

54 of 54 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

24 Own interpretation · 20 Not checked yet · 12 Own result · 9 No basis given · 1 Supported

Verify all 23 references — free account

Show all 36 claims

  • Probably not a substantial claim. 19
  • It may state two separate claims as one. 14
30 of 30
  • The paper relies on this without support.

    Simulation of quantum systems with a classical computer is, with the best known methods, in general inefficient.

    “Note also that the statements about the efficiency of the training procedure refer to the physical implementation with quantum technology: the simulation of quantum systems with a classical computer is, with the best known methods, in general inefficient.”
  • The paper relies on this without support.

    Several labs can implement the phase shifting via heaters or the electro-optic effect.

    “Several labs can implement the phase shifting via heaters or the electro-optic effect.”
2 of 2

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Citations

Cites

Show all 52 references

Research works printed but not linked: 1

  1. Hedemann, S. R. Hyperspherical parameterization of unitary matrices. Preprint at https://arxiv.org/abs/1303.5904 (2013). · arXiv

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Metadata

Authors
Wan, K. H., Dahlsten, O., Kristjánsson, H., Gardner, R., & Kim, M. S.
Affiliations
  • London Institute for Mathematical Sciences (GB)
  • Southern University of Science and Technology (CN)
  • Imperial College London (GB)
Corresponding author
Dahlsten, Oscar
Venue
npj Quantum Information
Published
2017-09-14
Volume
3
Issue
1
ISSN
2056-6387 (ISSN-L)
OpenAlex
W2560386163
Cited by
276
References
52
Citations by year
2026: 7 · 2025: 25 · 2024: 30 · 2023: 38 · 2022: 42 · 2021: 47 · 2020: 41 · 2019: 24 · 2018: 19 · 2017: 3
FWCI
14.19
Type
journal article
Language
en
Open access
Locations
  • npj Quantum Information (publishedVersion, cc-by)
  • arXiv (Cornell University) (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
  • Spiral (Imperial College London) (submittedVersion, cc-by)
  • arXiv (Cornell University)
Funders
  • Leverhulme Trust (RPG-2014-055)
  • Royal Society
  • European Commission (618074)
  • Engineering and Physical Sciences Research Council (EP/K034480, EP/K034480/1, K034480/1)
  • Division of Mathematical Sciences
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Computing Algorithms and Architecture
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Information and Cryptography
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum many-body systems
Keywords
quantum neural networks, feedforward neural networks, quantum autoencoders, quantum state compression, quantum teleportation, quantum communication protocols, photonics, gradient descent learning

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