Studying maximal entanglement and Bell nonlocality at an electron-ion collider

In this paper, we propose to test quantum entanglement and Bell nonlocality at an electron-ion collider (EIC). By computing the spin correlations in quark-antiquark pairs produced via photon-gluon fusion, we find that longitudinally polarized photons produce maximal entanglement at leading order, while transversely polarized photons generate significant entanglement near the threshold and in the ultrarelativistic regime. Compared to hadron colliders, the EIC provides a cleaner experimental environment for measuring entanglement through the γ * g → q q ¯ channel, offering a strong signal and a promising avenue to verify Bell nonlocality. This study extends entanglement measurements to the EIC, presenting new opportunities to explore the interplay of quantum information phenomena and hadronic physics in the EIC era.