Cited by 225Topological Materials and PhenomenaQuantum Mechanics and Non-Hermitian PhysicsAdvanced Condensed Matter Physics

Experimental measurement of the Berry curvature from anomalous transport

Open access
Wimmer, Martin, Price, Hannah M., Carusotto, Iacopo, Peschel, Ulf·2017·Nature Physics

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Written from the paper’s full text.

TL;DR

This paper reports the first direct optical measurement of Berry curvature by tracking anomalous wavepacket transport in a photonic mesh lattice made from two coupled fibre loops. The measured Berry curvature for a Floquet band agrees well with theory and demonstrates that wavepacket dynamics can map local band geometry without reconstructing eigenstates.

Key findings

  • The authors directly observed Berry-curvature-induced anomalous displacement in an optical system, which they describe as the first such direct measurement in photonics and the first full tomography of Berry curvature from anomalous transport.
  • For a wavepacket centred near \(Q = 0.1\pi\) with phase gradient \(\phi_0 = \pi/50\), they measured an anomalous displacement of up to about 1 position over 200 time steps.
  • The reconstructed Berry curvature captured the expected symmetry, sign, and magnitude over much of the band, including the relation \(\Omega^1_{\phi,Q} = -\Omega^2_{\phi,Q}\) between the two bands.
  • The method worked even along trajectories approaching band singularities, although measurements became meaningless after population transfer at the singularity.

Methods

  • Pulses at \(\lambda = 1{,}555\) nm were injected into two coupled fibre loops with average round-trip time \(T \approx 5{,}200\) ns and loop-length difference corresponding to \(\Delta T \approx 35.4\) ns; pulse width was 25 ns, limiting unambiguous sequences to about \(T/\Delta T \approx 147\) pulses.
  • A time-dependent phase modulation with alternating sign every round trip engineered Floquet quasi-energy bands; the phase magnitude was slowly ramped to pump the wavepacket, and the centre-of-mass shift was measured for opposite phase gradients \(\pm \phi_0\) to isolate Berry curvature from group velocity.
  • Wavepackets with narrow momentum spread \(\Delta Q \approx 0.05\pi\) were prepared over 200 steps and measured over the next 200 steps; \(Q\) was scanned from \(-\pi\) to \(\pi\) in steps of \(0.05\pi\), measurements were averaged over about 25 realizations, and Berry curvature was extracted by numerical differentiation after a moving-average filter with span 5.

Limitations

  • The paper states that the bands are not gapped, so adiabatic evolution across the full parameter space breaks down and the quantized Thouless-pumping relation is not applicable; near band-touching points adiabaticity fails and the protocol no longer gives meaningful measurements after population transfer.
  • The paper notes that sequence length is limited to roughly 147 pulses by the need to label pulses unambiguously, and that additional components introduce losses of about 8 dB per round trip, compensated by erbium-doped fibre amplifiers; the experiments use classical coherent bright light and do not rely on quantum effects.
  • Evident from the text: the Berry curvature reconstruction depends on numerical differentiation and smoothing of the measured centre-of-mass shift, and the main demonstration is a proof-of-principle in one photonic platform, with a second modulation example relegated to Supplementary Information.

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

Integrity signals

Registry

Crossref · 10.1038/nphys4050

Cites

37 of 37 references verified0 citation errors · 0 not checkable

Statistics

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Claims the paper makes

0 of 19 cited sources checked · 0 supported · 0 flagged

  • Findingreasoning
    § Experimental measurement of the Berry curvature from anomalous transport

    With the alternating phase modulation, the two bands satisfy cos θ = 1/2(cos Q - cos φ).

    “cos θ = 1 2 (cos Q -cos ϕ) (6)”
    Quote in the paperSubstantial claim
  • Findingown data
    § Experimental measurement of the Berry curvature from anomalous transport

    The work provides the first direct measurement or observation of Berry curvature effects in an optical system.

    “This is both the first direct observation of Berry curvature effects in an optical system, and a proof-ofprinciple demonstration that wavepacket dynamics can serve as a high-resolution tool for mapping out geometric properties.”
    • Also stated in: § Experimental measurement of the Berry curvature from anomalous transport · boosted
      “In this Letter, we go beyond previous experiments to provide the first direct measurement of the Berry curvature in an optical system.”
    Quote in the paperSubstantial claim
  • Findingreasoning
    § Experimental measurement of the Berry curvature from anomalous transport

    The separation of timescales allows clearly separated pulse sequences, so each pulse can be labelled by two integers (m,n).

    “Thanks to the separation of all of these timescales, we observe clearly separated sequences of pulses over time (see Fig. 1), so that each pulse can be straightforwardly labelled by two integers (m, n)”
    Quote in the paperSubstantial claim
  • Findingown data
    § Experimental measurement of the Berry curvature from anomalous transport

    The local Berry curvature is mapped directly from anomalous transport for the first time by discrete differentiation of the lateral shift.

    “We exploit this to map out the local Berry curvature directly from anomalous transport for the first time, by performing a discrete differentiation of the lateral shift n j (M) as (see Fig. 3c)”
    Quote in the paperSubstantial claim
  • Findingreasoning
    § Experimental measurement of the Berry curvature from anomalous transport

    Without phase shift, the quasi-energy band structure satisfies cos θ = 1/2(cos Q - 1).

    “cos θ = 1 2 (cos Q -1)(5)”
    Quote in the paperNot a substantial claim
  • May combine two claims. 10
  • Classified as probably not a substantial claim. 7
  • May combine two claims.

    Findingown data
    § Experimental measurement of the Berry curvature from anomalous transport

    The Berry curvature for these bands is singular where the two bands touch but otherwise takes large non-zero positive and negative values across the effective 2D parameter space.

    “As shown in Fig. 2d, this Berry curvature is singular at points where the two bands touch but otherwise can take large non-zero positive and negative values across the effective 2D parameter space.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingreasoning
    § Experimental measurement of the Berry curvature from anomalous transport

    The two bands are periodic in Q and θ and have a band-touching at Q = ±π.

    “leading to two bands that are periodic in both Q and θ as expected in a Floquet system, with a band-touching at the edge of the 1D Brillouin zone where Q = ±π”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Findingown data
    § Experimental measurement of the Berry curvature from anomalous transport

    The experimental reconstruction captures the main features of Berry curvature, including overall symmetry and sign, quantitative magnitude over much of the band, and the complementarity Ω1 = -Ω2.

    “as can be seen, the main features of the Berry curvature are well captured, such as the overall symmetry and sign, the quantitative magnitude over much of the band and the predicted complementarity of the two bands 1,26 (that is, Ω ϕ,Q 1 = -Ω ϕ,Q 2 ).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [1] Xiao, D., Chang, M.-C. & Niu, Q. Berry phase effects on electronic properties. Rev. Mod. Phys. 82, 1959–2007 (2010). source

      Not checked in the free run.

    • cites [26] Fläschner, N. et al. Experimental reconstruction of the Berry curvature in a Floquet Bloch band. Science 352, 1091–1094 (2016). source

      Not checked in the free run.

  • May combine two claims.

    Findingown data
    § Experimental measurement of the Berry curvature from anomalous transport

    Near Q ≈ 0, Berry curvature can be extracted until the singularity at φ = π; after that, population transfer to the other band makes the measurement no longer meaningful.

    “Close to the centre of the Brillouin zone (Q ≈ 0), for example, we can extract the Berry curvature until the singularity is hit at ϕ = π; afterwards, part of the population is transferred to the other band and the measurement is no longer meaningful.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

    Interpretationcitation
    § Experimental measurement of the Berry curvature from anomalous transport

    The method's versatility should allow it to be applied in configurations including systems with gain and loss and/or nontrivial topological invariants.

    “This versatility of this scheme should allow it to be applied in a variety of configurations, including systems with gain and loss 32 and/or nontrivial topological invariants.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [32] Regensburger, A. et al. Parity-time synthetic photonic lattices. Nature 488, 167–171 (2012). source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductown data

    The error bars in Fig. 2e are estimated from the spectral width ΔQ ≈ 0.05π horizontally and the 95% confidence fit uncertainty vertically.

    “The error bars depicted in Fig. 2e are estimated by the spectral width Q ≈ 0.05π of the initial excitation in the horizontal direction and by the uncertainty of the fit procedure for a 95% confidence level in the vertical direction.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Study design and conductreasoning
    § Experimental measurement of the Berry curvature from anomalous transport

    The integer labelling is limited to sequences shorter than the round-trip time, limiting the maximum number of pulses in a sequence to about 147.

    “Of course, this picture is restricted to sequences shorter than the round trip time in order for the assignment of integers to be unambiguous; this limits the maximum number of pulses in a given sequence to T / T ≈ 147.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductreasoning
    § Experimental measurement of the Berry curvature from anomalous transport

    Dispersive effects in the optical fibres are typically unimportant even over 400 round trips.

    “Thanks to the long pulse-width, T pulse , dispersive LETTERS effects in the optical fibres are typically unimportant, even over 400 round trips, corresponding to 400 km of propagation.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Study design and conductreasoning
    § Experimental measurement of the Berry curvature from anomalous transport

    The experiments use classical coherent bright light pulses and do not rely on quantum effects.

    “In general, the use of these amplifiers destroys quantum correlations; however, all experiments here are performed with a classical, coherent bright light pulse and do not rely on quantum effects.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Premisereasoning
    § Experimental measurement of the Berry curvature from anomalous transport

    The topological Thouless pumping limit is recovered for a filled gapped band after a complete adiabatic pump cycle, with the shift quantized as the Chern number.

    “We note that the limit of topological Thouless pumping can be recovered from this expression, if we consider the motion of a filled and gapped energy band after a complete adiabatic pump cycle.Then, the shift is quantized as an integer 3”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [3] Thouless, D. J. Quantization of particle transport. Phys. Rev. B 27, 6083–6087 (1983). source

      Not checked in the free run.

  • May combine two claims.

    Study design and conductreasoning
    § Experimental measurement of the Berry curvature from anomalous transport

    In the experiment, the energy bands are not gapped, so the assumption of adiabatic evolution across the entire 2D parameter space breaks down and the quantized Thouless pumping expression is not applicable.

    “In our experiment, however, we consider a system in which the energy bands are not gapped and so the assumption of adiabatic evolution across the entire 2D parameter space breaks down and equation ( 12) is not applicable.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationown data
    § Experimental measurement of the Berry curvature from anomalous transport

    The method measures Berry curvature directly from wavepacket dynamics without requiring full reconstruction of band eigenstates.

    “with the significant advantage that it does not require a full reconstruction of the band eigenstates as an intermediate step.”
    • Also stated in: § Experimental measurement of the Berry curvature from anomalous transport · plain
      “After exciting an initial eigenstate, no further information about the eigenstates is required as we directly measure the Berry curvature from its physical consequences on wavepacket dynamics”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [26] Fläschner, N. et al. Experimental reconstruction of the Berry curvature in a Floquet Bloch band. Science 352, 1091–1094 (2016). source

      Not checked in the free run.

    • cites [27] Li, T. et al. Bloch state tomography using Wilson lines. Science 352, 1094–1097 (2016). source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation
    § Experimental measurement of the Berry curvature from anomalous transport

    The integral of Berry curvature over the 2D Brillouin zone determines the Chern number, a global topological invariant underlying quantization of Hall transport for a filled 2D band.

    “In a twodimensional (2D) quantum Hall system, for example, the integral of the Berry curvature over the 2D Brillouin zone determines the Chern number: a global topological invariant that underlies the quantization of Hall transport for a 2D filled energy band 2 .”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [2] Thouless, D. J., Kohmoto, M., Nightingale, M. P. & den Nijs, M. Quantized Hall conductance in a two-dimensional periodic potential. Phys. Rev. Lett. 49, 405–408 (1982). source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Experimental measurement of the Berry curvature from anomalous transport

    Thouless showed an analogous topological quantization of particle transport in a 1D band insulator when the lattice potential is slowly and periodically modulated.

    “As first explained by Thouless 3 , there can be an analogous topological quantization of particle transport in a 1D band insulator, when the lattice potential is 'pumped' , that is, is slowly and periodically modulated in time.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [3] Thouless, D. J. Quantization of particle transport. Phys. Rev. B 27, 6083–6087 (1983). source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Study design and conductnone given
    § Experimental measurement of the Berry curvature from anomalous transport

    The slow variation of the phase magnitude adiabatically pumps the system provided the rate φ0 is sufficiently small compared with the bandgap.

    “while the slow variation in equation ( 8) adiabatically 'pumps' the system, provided that the rate ϕ 0 is sufficiently small compared with the bandgap.”
    Quote in the paperSubstantial claim
    • The authors state this as an assumption: The slow variation of the phase magnitude adiabatically pumps the system when the rate is sufficiently small compared with the bandgap.
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    The measured propagation was averaged over approximately 25 realizations to reduce noise.

    “To reduce the noise limit of the data acquisition, the measured propagation was averaged over approximately 25 realizations.”
    Quote in the paperNot a substantial claim
16 of 16
  • The authors state this as an assumption.

    Dispersion effects are neglected in the model.

    “we have neglected here dispersion effects and assumed that the pulse shape does not depend on the specific route taken.”
  • The authors state this as an assumption.

    The pulse shape does not depend on the specific route taken through the loops.

    “we have neglected here dispersion effects and assumed that the pulse shape does not depend on the specific route taken.”
  • The authors state this as an assumption.

    The slow variation of the phase magnitude adiabatically pumps the system when the rate is sufficiently small compared with the bandgap.

    “while the slow variation in equation ( 8) adiabatically 'pumps' the system, provided that the rate ϕ 0 is sufficiently small compared with the bandgap.”
3 of 3

Claims other papers make about this one

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  • The topological invariant was already employed in Ref. 28 to characterize crystalline topological superconductors.

    “Our topological invariant, which was already employed in Ref. 28 to characterize crystalline topological superconductors”

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Authors
Wimmer, M., Price, H. M., Carusotto, I., & Peschel, U.
Affiliations
  • Friedrich-Alexander-Universität Erlangen-Nürnberg (DE)
  • University of Trento (IT)
  • Friedrich Schiller University Jena (DE)
Corresponding author
Peschel, Ulf
Venue
Nature Physics
Published
2017-02-27
Volume
13
Issue
6
Pages
545-550
ISSN
  • 1745-2473 (ISSN-L)
  • 1745-2481
OpenAlex
W2524593142
Cited by
225
References
37
Citations by year
2026: 16 · 2025: 27 · 2024: 34 · 2023: 26 · 2022: 26 · 2021: 29 · 2020: 24 · 2019: 15 · 2018: 22 · 2017: 6
FWCI
8.99
Type
journal article
Language
en
Open access
Locations
  • Nature Physics (publishedVersion)
  • University of Birmingham Research Portal (University of Birmingham) (publishedVersion, other-oa)
  • arXiv (Cornell University) (submittedVersion)
  • Iris (University of Trento) (submittedVersion)
  • arXiv (Cornell University)
Funders
  • European Commission (656093)
  • Deutsche Forschungsgemeinschaft (PE 523/14-1, GRK2101, /14-1)
  • Erlangen Graduate School of Advanced Optical Technologies
  • Provincia Autonoma di Trento
  • Horizon 2020 Framework Programme (640800)
Topics
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Topological Materials and Phenomena
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Mechanics and Non-Hermitian Physics
  • Physical Sciences › Physics and Astronomy › Condensed Matter Physics › Advanced Condensed Matter Physics
Keywords
Berry curvature, wave packet dynamics, anomalous transport, one-dimensional photonic crystals, optical pulses, topological invariants, Berry phase

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