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Cited by 11Orbital Angular Momentum in OpticsQuantum Information and CryptographyMetamaterials and Metasurfaces Applications

The DOI matches its Crossref record; 82 of the 82 references it cites were found in a registry or an index; 2 of the 7 sources its claims cite were checked for support.

Quantum skyrmions and high dimensional entanglement mediated by nanophotonics

Open access
Kam, Amit, Tsesses, Shai, Fridman, Lior, Ilin, Yigal, Sivan, Amir, Sayer, Guy, Lotan, Stav, Cohen, Kobi, Shaham, Amit, Nemirovsky-Levy, Liat, Popilevsky, Larisa, Karnieli, Aviv, Orenstein, Meir, Segev, Mordechai, Bartal, Guy·2026·eLight
DOI 10.1186/s43593-026-00124-1
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Abstract

Quantum nanophotonics offers essential tools and technologies for controlling quantum states, while maintaining a miniature form factor and high scalability. Nanophotonic platforms can transfer information from the traditional degrees of freedom (DoFs) of photons, such as spin angular momentum (SAM) and orbital angular momentum (OAM), to the DoFs of the nanophotonic platform—and back, opening new directions for quantum information processing. Recent experiments have utilized, for entanglement the total angular momentum (TAM) of a photon—as a unique DoF of nanophotonic platforms—for demonstrating entanglement in TAM. Here, we unravel the morphing of quantum states of heralded single photons as they couple into and out of the near-field of a nanophotonic system. Through quantum state tomography, we discover that the TAM state of the near-field transforms to a free-space entangled state within a larger Hilbert space of SAM and OAM. Furthermore, we show that this entangled single photon state is in fact a quantum optical Stokes skyrmion with a topological invariant of $$\pm 2$$ ± 2 . The concepts described here bring new ideas and methodologies in developing high-dimensional quantum circuitry on a chip.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

The paper tracks heralded single photons as they couple into and out of a plasmonic nanophotonic platform, showing that near-field total-angular-momentum (TAM) qubits become free-space qudits entangled in spin and orbital angular momentum (SAM and OAM). Quantum state tomography reconstructs the density matrices and Wigner functions, with state preparation fidelity above 97%.

Key findings

  • Near-field TAM qubits, generated by coupling single photons into surface plasmon polariton modes, transform on out-coupling into free-space single-photon qudits entangled in SAM and OAM; the paper gives explicit mappings such as \(|J_1\rangle \mapsto \frac{1}{\sqrt{2}}(|\sigma_-\rangle|l=2\rangle - |\sigma_+\rangle|l=0\rangle)\).
  • Quantum state tomography of the free-space qudits yields density matrices for four incident polarizations, with experimental results coinciding with theory at higher than \(97 \pm 2.2\%\) fidelity.
  • The reconstructed four-dimensional Wigner distribution shows negative values, attesting to non-classicality, and a single ring expected for the Fock state \(|1\rangle\); middle-column projections show nonclassical correlations between phase-space coordinates of different modes, evidencing entanglement.
  • The measured Wigner function differs from the ideal one by an asymmetry on the order of \(10^{-2}\), which the authors attribute to partial presence of the \(|J_{-1}\rangle\) state in the system’s basis.

Methods

  • The platform is a gold–air interface patterned with a circular grating that couples light into SPP modes carrying angular momentum, plus a concentric annular slit that couples SPPs back into free-space photons.
  • Heralded single photons are produced by spontaneous parametric down-conversion: a 404 nm CW laser is directed into a BBO type-II crystal, photon pairs are filtered to 808 nm, separated by a polarizing beam splitter, and one photon triggers an EMCCD camera while the other is launched into the nanophotonic platform.
  • Quantum state tomography is performed by launching photons at four polarizations (\(|H\rangle\), \(|V\rangle\), \(|\sigma_-\rangle\), \(|\sigma_+\rangle\)) and projecting the scattered photon onto four polarization components; a mean squared error estimator fits each measurement to superpositions of Bessel or Hermite–Bessel modes, and the density matrix and Wigner distribution are reconstructed.

Limitations

  • The text states that reflected projections are ignored in the out-coupling model.
  • The measured Wigner function shows an asymmetry on the order of \(10^{-2}\), which the authors attribute to the partial presence of the \(|J_{-1}\rangle\) state in the system’s basis.
  • Evident from the text: the experiment uses single heralded photons and four input polarizations; higher-order entanglement by coupling multiple photons is proposed as future work rather than demonstrated.

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

Integrity signals

Registry

Crossref · 10.1186/s43593-026-00124-1

Cites

82 of 82 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

2 of 7 cited sources checked · 0 supported · 0 flagged · accuracy not yet measured

  • Premisecitation

    SPPs generated in such a circularly-symmetric nanophotonic platform are either eigenstates or coherent superpositions of the TAM operator, with a TAM value equal to that of the incident free-space photon whose TAM is the sum of its SAM and OAM values.

    “In general, SPPs generated in such circularly-symmetric nanophotonic platform are either eigenstates or coherent superpositions of the TAM operator, with a TAM value equal to that of the incident free space photon whose TAM is the sum of its SAM and OAM values 36 .”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [36] P. Ornelas, I. Nape, R. de Mello Koch, A. Forbes, Non-local skyrmions as topologically resilient quantum entangled states of light. Nat. Photonics 18, 258–266 (2024) source

      Split into 2 atoms — 0 confirmed, 0 partially supported, 0 disputed, 0 misattributed, 2 unverifiable. Expand the claim to see per-atom verdicts.

      Experimental — accuracy not yet measured
  • Findingown data

    The measured results agree with the theoretical Wigner distribution to an excellent degree.

    “Our measured results agree with the theoretical Wigner distribution to an excellent degree, as seen from the differences between the theoretical and measured 2D projections of the Wigner distributions, shown in Fig. 4.b.”
    Quote in the paperSubstantial claim
  • Findingown data

    The state preparation fidelity of the near-field TAM qubits is above 97%.

    “The extracted density matrix and Wigner function in free-space indicate state preparation fidelity above 97%.”
    • Also stated in: § Main · plain
      “By reconstructing the photonic density matrix and Wigner function, we identify that the state preparation fidelity of the near-field TAM qubits is above 97%.”
    • Also stated in: § Discussion and Outlook · plain
      “The experimental results coincide with theoretical results with higher than 97 ± 2.2% fidelity.”
    Quote in the paperSubstantial claim
  • Findingreasoning

    The two right-hand projections do not exhibit correlations between the R(α), I(β) and R(β), I(α) phase-space cross-mode coordinate pairs.

    “The two projections on the right-hand side of Fig. 4.a do not exhibit correlations between the ℜ(𝛼), ℑ(𝛽) and ℜ(𝛽), ℑ(𝛼) phase-space cross-mode coordinate pairs, since they can be decomposed into a sum of products of the single-mode Wigner distributions corresponding to the Fock states |0⟩ and |1⟩, see supplementary.”
    Quote in the paperNot a substantial claim
  • Findingown data

    The TAM qubit in the near-field becomes a free-space qudit entangled in the photonic SAM and OAM.

    “Through quantum state tomography, we discover that the TAM qubit in the near-field becomes a freespace qudit entangled in the photonic SAM and OAM.”
    • Also stated in: § Main · plain
      “These qubits are then scattered out into free space where they become single photonic qudits, entangled in their SAM and OAM.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim. 7
  • It may state two separate claims as one. 9

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Premisecitation

    Dissipative and entangling circuits have recently been shown to enable methods for preparing a wide range of ground states, facilitate representation of nontrivial thermal states with enhanced noise resilience, and eliminate the barren plateau effect in training quantum neural networks.

    “Such dissipative and entangling circuits have recently been shown to enable methods for preparing a wide range of ground states, facilitating the representation of nontrivial thermal states with significantly enhanced noise resilience 47 , and able to eliminate the barren plateau effect in the training of quantum neural networks 48 .”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [47] Y. Shen et al., Optical skyrmions and other topological quasiparticles of light. Nat. Photonics 18, 15–25 (2024) source

      Split into 3 atoms — 0 confirmed, 0 partially supported, 0 disputed, 0 misattributed, 3 unverifiable. Expand the claim to see per-atom verdicts.

      Experimental — accuracy not yet measured
    • cites [48] S. Tsesses, K. Cohen, E. Ostrovsky, B. Gjonaj, G. Bartal, Spin-orbit interaction of light in plasmonic lattices. Nano Lett. 19, 4010–4016 (2019) source

  • It may state two separate claims as one.

    Findingown data

    The Wigner distribution panels display negative values, attesting to the non-classical nature of the state, and a single ring as expected for the Fock state |1⟩.

    “The panels display negative values that attest to the non-classical nature of the state and a single ringas expected of a Wigner distribution for the Fock state |1⟩.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Findingown data

    The nanophotonic platform generated entangled single-photon states and the evolution of the quantum information they carry, associated with angular momentum, was systematically explored as it couples into and out of the platform.

    “In conclusion, we generated entangled single-photon states using a nanophotonic platform and systematically explored the evolution of the quantum information they carry, which is associated with angular momentum, as it couples into and out of the photonic platform.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.

    Study design and conductnone given

    The imaging system is set in the Fourier plane of the platform, allowing it to image the shape of the modes.

    “The imaging system is set in the Fourier plane of the platform, allowing it to image the shape of the modes.”
    Quote in the paperNot a substantial claim

  • It may state two separate claims as one.

    Interpretationreasoning

    This entanglement is a unique result of the fact that the angular momentum of the vector SPP mode is solely characterized by the observable TAM, and that only two combinations of SAM and OAM can satisfy Maxwell's equations when light is coupled to the far-field.

    “This entanglement is a unique result of the fact that the angular momentum of the vector SPP mode is solely characterized by the observable TAM, and that only two combinations of SAM and OAM can satisfy Maxwell's equations when light is coupled to the far-field.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: Only two combinations of SAM and OAM can satisfy Maxwell's equations when light is coupled to the far-field.
    • Rests on an assumption: The angular momentum of the vector SPP mode is solely characterized by the observable TAM.

  • Probably not a substantial claim. It may state two separate claims as one.

    Study design and conductnone given

    On average, only one pixel is turned on by a single photon, and the camera records its position in the image plane of the structure output.

    “On average, only one pixel is turned on by a single photon, and the camera records its position in the image plane of the structure output.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim. It may be too vague to check against evidence. The paper’s conclusions may not depend on it.

    Interpretationnone given

    The nanophotonic platform is well-suited for integration with a wide range of on-chip photonic circuits.

    “Our platform is well-suited for integration with a wide range of on-chip photonic circuits and could be extended to achieve higher-order entanglement by coupling multiple photons to the nanophotonic system, advancing on-chip quantum technologies.”
    Quote in the paperNot a substantial claim

  • It may state two separate claims as one.

    Interpretationreasoning

    The nanophotonic mode is shaped as a Bessel function of the first kind of order -1 (+1), carrying a -ħ (+ħ) quantum of angular momentum.

    “Namely, the nanophotonic mode is shaped as a Bessel function of the first kind of order -1 (+1), carrying a -ℏ (+ℏ) quantum of angular momentum.”
    Quote in the paperSubstantial claim

  • It may state two separate claims as one.

    Interpretationreasoning

    The quantum system is both dissipative and entangling.

    “Consequently, the quantum system is both dissipative and entangling.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The reduction in degrees of freedom in the near-field is modeled as a dissipative operation where the action on a single-qubit state |ψ⟩ is |ψ⟩ → |0⟩.

  • Probably not a substantial claim. It may state two separate claims as one.

    Study design and conductown data

    Heralded detection was used, separating two photons generated via spontaneous parametric down-conversion and using one to trigger an EMCCD camera, ensuring it only detects coincident single photon events.

    “The first (heralding) photon is coupled into a single-mode fiber and sent to a single-photon detector, whose signal triggers the EMCCD camera and ensures it only detects coincident single photon events.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim.

    Premisecitation

    QST determines the quantum-mechanical state of a system by measuring various non-commuting observables on an ensemble of identically-prepared system copies, enabling extraction of the density matrix in a predetermined fashion.

    “QST determines the quantummechanical state of a system by measuring various non-commuting observables on an ensemble of identically-prepared system copies, enabling the extraction of the density matrix in a predetermined fashion.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [49] S. Gao et al., Paraxial skyrmionic beams. Phys. Rev. A 102, 053513 (2020) source

      Checked before — its earlier verdict is held back until a new check runs.

    • cites [50] W. Lin, Y. Ota, Y. Arakawa, S. Iwamoto, On-chip optical skyrmionic beam generators. Optica 11, 1588 (2024) source

      Checked before — its earlier verdict is held back until a new check runs.

  • Probably not a substantial claim. The paper may give no reason why it holds.

    Interpretationnone given

    The ideal coupling of the input field into the nanophotonic mode facilitates the generation of a qubit encoded in the TAM basis.

    “The ideal coupling of the input field into the nanophotonic mode facilitates the generation of a qubit encoded in the TAM basis.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The coupling of the input field into the nanophotonic mode is ideal.
12 of 12

  • The authors state this as an assumption.

    The nanophotonic system can be modeled as a non-unital quantum channel represented by a non-unitary quantum circuit.

    “It is convenient to model the nanophotonic system as a non-unital quantum channel represented by a non-unitary quantum circuit, as shown in Fig. 1b which has been studied in the context of learning local quantum channels 46 .”

  • The authors state this as an assumption.

    The reduction in degrees of freedom in the near-field is modeled as a dissipative operation where the action on a single-qubit state |ψ⟩ is |ψ⟩ → |0⟩.

    “The reduction in degrees of freedom in the near-field is modeled as a dissipative operation, where the action on a single-qubit state |𝜓⟩ is represented as |𝜓⟩ → |0⟩.”

  • The paper relies on this without support.

    The paraxial approximation holds in the far-field of the annular coupler.

    “However, in the far-field of the annular coupler, the angular momentum of the scattered field can be decomposed to its SAM and OAM constituents, since the paraxial approximation holds.”

  • The authors state this as an assumption.

    The reflected projections can be ignored.

    “The transversal nature of propagating electromagnetic waves results in scattering of the in-plane components of the SPP field, projecting the eigenstate of the TAM operator in the near-field onto the eigenstate of the TAM in free space (we ignore here the reflected projections).”

  • The paper relies on this without support.

    The coupling of the input field into the nanophotonic mode is ideal.

    “The ideal coupling of the input field into the nanophotonic mode facilitates the generation of a qubit encoded in the TAM basis.”

  • The paper relies on this without support.

    Only two combinations of SAM and OAM can satisfy Maxwell's equations when light is coupled to the far-field.

    “This entanglement is a unique result of the fact that the angular momentum of the vector SPP mode is solely characterized by the observable TAM, and that only two combinations of SAM and OAM can satisfy Maxwell's equations when light is coupled to the far-field.”

  • The paper relies on this without support.

    The angular momentum of the vector SPP mode is solely characterized by the observable TAM.

    “This entanglement is a unique result of the fact that the angular momentum of the vector SPP mode is solely characterized by the observable TAM, and that only two combinations of SAM and OAM can satisfy Maxwell's equations when light is coupled to the far-field.”
7 of 7

Citations

Cites

Flagged first, then by citations

Research works printed but not linked: 1

  1. A. Pesah et al., Absence of barren plateaus in Quantum Convolutional Neural Networks. Phys. Rev. X 11, 041011 (2021)

Cited by

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Metadata

Authors
Kam, A., Tsesses, S., Fridman, L., Ilin, Y., Sivan, A., Sayer, G., Lotan, S., Cohen, K., Shaham, A., Nemirovsky-Levy, L., Popilevsky, L., Karnieli, A., Orenstein, M., Segev, M., & Bartal, G.
Affiliations
Technion – Israel Institute of Technology (IL)
Corresponding author
Bartal, Guy
ORCID
Venue
eLight
Publisher
Springer Science and Business Media LLC
Published
2026-04-07
Volume
6
Issue
1
ISSN
  • 2097-1710 (ISSN-L)
  • 2662-8643
DOI
10.1186/s43593-026-00124-1
OpenAlex
W4417170791
Semantic Scholar
0e0483e73c39f3ccf72ddd4c4c44b16287ea79c5
Cited by
11
References
81
Citations by year
2026: 11
FWCI
14.42
Type
journal article
Language
en
Open access
Licence
Locations
  • eLight (publishedVersion, cc-by)
  • arXiv (Cornell University) (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
  • arXiv (Cornell University)
Funders
  • MAGNET program (73756)
  • Israel Science Foundation (3620/24)
  • Deutsche Forschungsgemeinschaft (SE 2153/3-1)
Topics
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Orbital Angular Momentum in Optics
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Information and Cryptography
  • Physical Sciences › Materials Science › Electronic, Optical and Magnetic Materials › Metamaterials and Metasurfaces Applications
Keywords
quantum skyrmions, quantum nanophotonics, spin angular momentum, orbital angular momentum, near-field coupling, heralded single photons, quantum state tomography, topological invariants, high-dimensional entanglement

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