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Experimental simulation of Dirac equation in superconducting qubits

Open access
Zhang, Yu, Xu, Jianwen, Ma, Zhuang, Zheng, Wen, Lan, Dong, Tan, Xinsheng, Yu, Yang·2025·Communications Physics

Abstract

The Dirac equation elucidates fundamental physical principles and predicts significant physical phenomena. Its simulation further offers explanations for subsequent physics observations. We map the 3+1-dimensional Dirac equation onto the first excited manifold of four qubits to simulate the internal four-component spinor dynamics. Additionally, we simulate two intriguing and challenging-to-implement physical phenomena: the Zitterbewegung effect and the Sauter-Schwinger effect. Compared to previous simulations, our system provides a larger parameter space, allowing for a more comprehensive exploration of physical properties. This work enhances our understanding of spinor dynamics. The Dirac equation, one of the most fundamental equations in relativistic quantum mechanics, has influenced diverse research fields. The authors demonstrate an analogue simulation of the 3+1-dimensional Dirac equation by applying parametric modulations in superconducting circuits.

AI snapshot

Written from the paper’s full text.

TL;DR

The paper reports an analogue simulation of the 3+1-dimensional Dirac equation using the first-excited manifold of four superconducting qubits, mapping spinor dynamics and measuring the Zitterbewegung and Sauter-Schwinger effects. It demonstrates velocity oscillations and mass-dependent pair production in a parameter space larger than prior 1+1-dimensional simulations.

Key findings

  • Free Dirac dynamics were simulated with momentum \(p=(1.3\,\text{MHz},0,0)\) and mass varied from \(0\,\text{MHz}\) to \(2.6\,\text{MHz}\); populations showed single-frequency oscillation, heavier particles oscillated faster, and state \(|3\rangle\) was never populated in the ideal description.
  • The Zitterbewegung effect was observed by directly measuring velocities \(v_x\) and \(v_y\) via quantum state tomography; with \(p=(1.3/\sqrt{2}\,\text{MHz},1.3/\sqrt{2}\,\text{MHz},0)\), the square of the ZBW oscillation frequency \(\omega_Z\) increased linearly with \(m^2\), and oscillations appeared only in \(v_y\) when momentum was solely in the \(x\)-direction.
  • The Sauter-Schwinger effect was simulated by chirping momentum from \(p_{\text{ini}}=(-2.6\,\text{MHz},0,0)\) to \(p_{\text{fin}}=(2.6\,\text{MHz},0,0)\) with rate \(|\epsilon|=(2.034\,\text{MHz})^2\); pair-production probability decreased with increasing mass, consistent with the Schwinger formula, and the effective electric field reached or surpassed the Sauter-Schwinger limit \(E\approx1.32\times10^{18}\,\text{V}\,\text{m}^{-1}\).
  • At large mass, a slight oscillation of \(|3\rangle\) was observed and attributed to deviation of the coupling strength’s phase caused by the shift of the resonant parametric frequency when all four parametric modulations were applied.

Methods

  • Four superconducting qubits were arranged in a 2D square, with adjacent qubits connected by a floating tunable coupler; each qubit had individual flux and XY control lines and a coplanar waveguide readout resonator for simultaneous multi-tone readout.
  • The 3+1D Dirac Hamiltonian was mapped onto the first-excited manifold of the four qubits using parametric modulation; coupling strengths were set as \(\Omega_{01}e^{-i\phi_1}=p_x-ip_y\), \(\Omega_{02}e^{-i\phi_2}=p_z-im\), \(\Omega_{23}e^{-i\phi_3}=p_x-ip_y\), and \(\Omega_{13}e^{-i\phi_4}=-p_z+im\), followed by a permutation to a supersymmetric representation.
  • Measurements used simultaneous readout of all qubits and quantum state tomography with two \(\sqrt{i\text{SWAP}}\)-like gates and four tomography phases \(\phi_m=m\pi/2\) to extract velocity expectation values; for the Schwinger effect, Landau-Zener rates were extracted from measured populations with readout error mitigation.

Limitations

  • Stated: velocity oscillations decay due to energy decay and pure dephasing in the superconducting qubits.
  • Stated: the slight \(|3\rangle\) oscillation at large mass is caused by coupling-strength phase deviation from the resonant parametric frequency shift when all four parametric modulations are applied.
  • Stated: for the Schwinger simulation, when mass exceeds \(1.5\,\text{MHz}\), the population increases because the Landau-Zener rate formula is not applicable within the experimental parameter regime; the deviation is caused by the finite maximum effective coupling strength. Evident from the text: the work is an analogue simulation limited to specific momenta, masses, and a four-qubit manifold, not a direct observation of the real high-energy phenomena.

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

Integrity signals

Registry

Crossref · 10.1038/s42005-025-02112-2

Cites

67 of 67 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

1 of 2 cited sources checked · 1 supported · 0 flagged

  • Premisecitation
    § Experimental simulation of Dirac equation in superconducting qubits Check for updates

    Experimental simulations of the Dirac equation in 3+1 dimensions remain lacking.

    “Experimental simulations of the Dirac equation in 3+1 dimensions remain lacking.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [62] Svetitsky, E. & Katz, N. Dirac particle dynamics of a superconducting circuit. Phys. Rev. A 99, 042308 (2019). source
  • Findingown data
    § Experimental simulation of Dirac equation in superconducting qubits Check for updates

    The 3+1-dimensional Dirac equation was simulated using four superconducting qubits in the first-excited manifold, mapping the four-component spinor dynamics.

    “We map the 3+1-dimensional Dirac equation onto the first excited manifold of four qubits to simulate the internal fourcomponent spinor dynamics.”
    • Also stated in: § Conclusions · boosted
      “we have demonstrated an analogue simulation of the 3+1 dimensional Dirac equation using superconducting circuits.”
    Quote in the paperSubstantial claim
  • Findingown data
    § Experimental simulation of Dirac equation in superconducting qubits Check for updates

    The Sauter-Schwinger effect was simulated by constructing an effective electric field whose strength reaches or surpasses the Sauter-Schwinger limit.

    “we demonstrate the Schwinger effect by constructing an effective electric field whose strength reaches or even surpasses the Sauter-Schwinger limit.”
    Quote in the paperSubstantial claim
  • Findingown data

    A slight oscillation of |3> is observed with a large mass.

    “In practice, we observe a slight oscillation of |3i with a large mass.”
    Quote in the paperNot a substantial claim
  • Findingown data
    § Experimental simulation of Dirac equation in superconducting qubits Check for updates

    The Zitterbewegung effect was observed in the superconducting qubit simulation.

    “Additionally, we simulate two intriguing and challenging-to-implement physical phenomena: the Zitterbewegung effect and the Sauter-Schwinger effect.”
    • Also stated in: § Conclusions · plain
      “we directly measured the velocities v x and v y using quantum state tomography and observed the ZBW due to the interference between the positive and negative energy components.”
    Quote in the paperSubstantial claim
  • May combine two claims. 8
  • Classified as probably not a substantial claim. 7
  • May combine two claims.

    Findingown data

    When the momentum in the y direction is reversed relative to Fig. 2b, the oscillation of v_x shifts by a phase of π, resulting in it being in phase with v_y.

    “When the momentum in the y direction is reversed relative to Fig. 2b, the oscillation of v x shifts by a phase of π, resulting in it being in phase with v y .”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Findingnone given

    When the mass is beyond 1.5 MHz, the population increases because the Landau-Zener rate formula is not applicable within the experiment parameter.

    “When the mass is beyond 1.5 MHz, the population increases because the formula of the Landau-Zener rate is not applicable within the experiment parameter.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Findingown data

    The remaining population in the {|0>,|1>} manifold characterizes the pair production and decreases with increasing mass.

    “The remaining population in f|0i; |1ig manifold characterizes the pair production, and it decreases with increasing mass.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Findingnone given

    The momentum in the x-direction can cause ZBW in the y-direction and vice versa.

    “the momentum in the x-direction can cause the ZBW in the y-direction and vice versa”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S4 (based).

    Interpretationnone given
    § Experimental simulation of Dirac equation in superconducting qubits Check for updates

    Compared to previous simulations, the system provides a larger parameter space, allowing more comprehensive exploration of physical properties.

    “Compared to previous simulations, our system provides a larger parameter space, allowing for a more comprehensive exploration of physical properties.”
    • Also stated in: § Zitterbewegung effect · plain
      “Our scheme provides larger parameter space than the previous 1+1 dimensional Dirac equation simulation, ensuring we explore more Dirac particle features.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Interpretationreasoning

    The evolution of a free Dirac particle can be described as Rabi oscillation between |0> and the bright state |B_0> in the V system, leading to no population transfer to |3>.

    “Therefore, the evolution of free Dirac particle can be described as the Rabi oscillation between |0i and bright state |Bi 0 in V system, leading that there is no population transfer to |3i as shown in the Fig.”
    Quote in the paperSubstantial claim
  • Classified as probably not a substantial claim.

    Study design and conductnone given

    The qubit frequencies and coupling strength were carefully designed to ensure the Dirac Hamiltonian could be constructed via parametric modulation.

    “The qubit frequencies and coupling strength are carefully designed to ensure we can construct the Dirac Hamiltonian via parametric modulation.”
    Quote in the paperSubstantial claim
  • Classified as probably not a substantial claim. May combine two claims.

    Premisenone given
    § Experimental simulation of Dirac equation in superconducting qubits Check for updates

    The Sauter-Schwinger limit requires an electric field E ≈ 1.32 × 10^18 V m^-1 to polarize the vacuum, making direct observation experimentally challenging.

    “The Sauter-Schwinger limit indicates that an electric field (E ≈ 1.32 × 10 18 V m -1 ) is required to polarize the vacuum, presenting a significant experimental challenge for direct observation.”
    Quote in the paperSubstantial claim
  • Classified as probably not a substantial claim.

    Premisenone given
    § Experimental simulation of Dirac equation in superconducting qubits Check for updates

    Direct experimental observation of Zitterbewegung is exceptionally challenging because its amplitude is on the order of the Compton wavelength (~10^-12 m) and its frequency is ~10^21 Hz.

    “ZBW predicts the rapid oscillatory motion of spin-1/2 particles, but the small amplitude (on the order of the Compton wavelength, ~10 -12 m) and high frequency ( ~10 21 Hz) make experimental observation exceptionally challenging.”
    Quote in the paperSubstantial claim
  • Classified as probably not a substantial claim.

    Study design and conductnone given

    The population measurements were corrected by readout error mitigation.

    “The population is corrected by readout error mitigation.(See Supplementary Note 5)”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationown data

    The sum of population |0> and |1> reflects the pair production rate, which corresponds with the Landau-Zener model.

    “The sum of the population |0i and |1i reflects the pair production rate, which corresponds with the Landau-Zener model as denoted in Fig. 3e.”
    Quote in the paperSubstantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductreasoning

    The results for different tomography phases were averaged to mitigate the effect of readout error in <σ_z>.

    “the data is redundant, so we average the results for different phases to mitigate the effect of readout error in 〈σ z 〉.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisenone given

    The Zitterbewegung effect results from interference between the positive and negative energy solutions of the Dirac equation.

    “the predicted super-fast rapid oscillation of relativistic particles, which results from the interference between the positive and negative energy solutions of the Dirac equation.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Study design and conductcitation

    The Landau-Zener rates were extracted from the measured populations and characterize the pair production rate.

    “The Landau-Zener rates are extracted from the measured populations 63 , and they characterize the pair production rate.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [63] Shevchenko, S., Ashhab, S. & Nori, F. Landau-Zener-Stückelberg interferometry. Phys. Rep. 492, 1–30 (2010). source
14 of 14

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • The stated tomography formula for v y is four times too large

    Minor

    The stated tomography relations make the eight-term numerator equal to four times the earlier expression for v y. Unlike the analogous v x formula, the final v y formula omits division by 4, so it would overstate the measured velocity.

1 of 1

Cites

Flagged first, then by citations

4 of the 71 references couldn’t be matched to a known paper.

Research works printed but not linked: 1

  1. Landau, L. To the theory of energy transmission in collissions. II. Phys. Zs. Sowjet 2, 46 (1932).

Cited by

Sorted by citations

Authors
Zhang, Y., Xu, J., Ma, Z., Zheng, W., Lan, D., Tan, X., & Yu, Y.
Affiliations
  • National Laboratory of Solid State Microstructures
  • University of Science and Technology of China (CN)
Corresponding author
  • Lan, Dong
  • Tan, Xinsheng
  • Yu, Yang
Venue
Communications Physics
Published
2025-06-12
Volume
8
Issue
1
ISSN
2399-3650 (ISSN-L)
OpenAlex
W4411240065
Cited by
3
References
71
Citations by year
2026: 3
FWCI
1.28
Type
journal article
Language
en
Open access
Locations
  • Communications Physics (publishedVersion, cc-by-nc-nd)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • National Science Foundation
  • National Natural Science Foundation of China (U21A20436, 11890704, 12074179)
  • Government of Jiangsu Province (BE2021015-1)
  • Natural Science Foundation of Shandong Province (ZR2023LZH002)
Topics
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Information and Cryptography
  • Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Quantum Mechanics and Applications
  • Physical Sciences › Computer Science › Artificial Intelligence › Quantum Computing Algorithms and Architecture
Keywords
Dirac equation, superconducting qubits, quantum simulation, Zitterbewegung, Schwinger effect, parametric modulation, superconducting circuits, relativistic quantum mechanics

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