“Quantum tomography of fermion pairs in e + e − collisions: Longitudinal beam polarization effects” (2026), by Yu-Chen Guo et al. Physics and Astronomy research paper. Original abstract below, unchanged. A free PDF is available.

Quantum tomography of fermion pairs in e + e − collisions: Longitudinal beam polarization effects

Yu-Chen Guo, Tao Han, Matthew Low et al. · November 5, 2026 · Physics and Astronomy

Abstract

We present a quantum tomography study of fermion pair production at future e⁺e⁻ colliders, emphasizing how longitudinal beam polarization controls the two-qubit spin density matrix. We study the processes e⁺ e⁻ → tt, e⁺e⁻→ μ⁺μ⁻ and Bhabha scattering e⁺e⁻→ e⁺e⁻, representing the mass threshold behavior, the Z pole resonance and the s/t-channel interplay. We choose to focus on three key concepts: quantum entanglement via the concurrence C, Bell nonlocality via the optimal Clauser Horne Shimony Holt (CHSH) parameter B, and non-stabilizerness (``magic'') via the second stabilizer Rényi entropy M₂. For the s-channel-dominated channels, longitudinal polarization mainly reshapes single-spin polarizations while leaving the spin-correlation matrix largely unchanged, rendering C and B comparatively robust, but inducing a pronounced variation of M₂. In contrast, in Bhabha scattering, polarization modifies the relative contributions of the s-channel and t-channel and can strongly affect all three observables. The observability of entanglement, Bell nonlocality, and magic exceeds the 5σ level when both statistical and systematic uncertainties are included, establishing the fermion pair systems as ideal laboratories for quantum-information studies in high energy leptonic collisions. With optimized beam polarization, future e⁺e⁻ colliders will provide a unique opportunity to experimentally explore and influence quantum resources in particle interactions.

Free PDF DOI: 10.1103/l5x9-z6zh