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Quantum Entanglement and Bell Nonlocality at Future Lepton Collider

Emidio Gabrielli, Luca Marzola

TL;DR

The paper investigates how quantum entanglement and Bell nonlocality can be explored in high-energy collider processes at future lepton colliders. Using a density-matrix tomography framework for bipartite spin states, it analyzes both qubit (tau-pair) and qutrit (diboson) systems, applying CHSH and CGLMP Bell tests. Standard Model predictions show measurable entanglement and nonlocality in tau-pair production with high significance (e.g., $\mathscr{C}\approx0.48$ and $\mathfrak{m}_{12}\approx1.24$ at FCC-like setups), and detectable nonlocality signals in $W^+W^-$ and $ZZ$ channels across relevant kinematic ranges. These results highlight the potential of future lepton colliders to probe fundamental quantum correlations in the electroweak sector with precision and offer a complementary platform to hadron colliders for testing quantum mechanics at high energies.

Abstract

Quantum entanglement and Bell nonlocality--cornerstones of quantum mechanics--have traditionally been investigated only in low-energy experimental settings. Only recently, these fundamental phenomena have come to be explored in the high-energy domain of particle physics, where collider experiments offer a powerful new platform for studying the phenomenology of quantum correlations. We present here recent results on the detection of entanglement and Bell nonlocality in processes such as tau-lepton, $WW$, and $ZZ$ pair production, illustrating the potential of Future Lepton Colliders to probe the quantum properties of fundamental interactions.

Quantum Entanglement and Bell Nonlocality at Future Lepton Collider

TL;DR

The paper investigates how quantum entanglement and Bell nonlocality can be explored in high-energy collider processes at future lepton colliders. Using a density-matrix tomography framework for bipartite spin states, it analyzes both qubit (tau-pair) and qutrit (diboson) systems, applying CHSH and CGLMP Bell tests. Standard Model predictions show measurable entanglement and nonlocality in tau-pair production with high significance (e.g., and at FCC-like setups), and detectable nonlocality signals in and channels across relevant kinematic ranges. These results highlight the potential of future lepton colliders to probe fundamental quantum correlations in the electroweak sector with precision and offer a complementary platform to hadron colliders for testing quantum mechanics at high energies.

Abstract

Quantum entanglement and Bell nonlocality--cornerstones of quantum mechanics--have traditionally been investigated only in low-energy experimental settings. Only recently, these fundamental phenomena have come to be explored in the high-energy domain of particle physics, where collider experiments offer a powerful new platform for studying the phenomenology of quantum correlations. We present here recent results on the detection of entanglement and Bell nonlocality in processes such as tau-lepton, , and pair production, illustrating the potential of Future Lepton Colliders to probe the quantum properties of fundamental interactions.
Paper Structure (8 sections, 5 equations, 2 figures)

This paper contains 8 sections, 5 equations, 2 figures.

Table of Contents

  1. Introduction
  2. The toolbox
  3. Qubits
  4. Qutrits
  5. Entanglement and nonlocality at lepton colliders
  6. Tau-lepton pair production
  7. $WW$ and $ZZ$ production
  8. Conclusions

Figures (2)

  • Figure 1: Standard Model predictions for the entanglement (quantified by the concurrence; left panel) and for nonlocality (right panel) in tau pair spin correlation as a function of the center of mass energy and scattering angle Fabbrichesi:2024wcd. Quantum entanglement is indicated by $\mathcal{C}>0$, while nonlocality is signaled by $\mathfrak{m}_{12}>1$.
  • Figure 2: The observables ${\@fontswitch\mathcal{I}}_{3}$ and $\mathscr{C}_2$ for the process $\ell^+\ell^-\to Z Z$ as functions of the diboson invariant mass and scattering angle in the center of mass frame. The hatched area in the plot on the left represents the bin in which nonlocal spin correlations are observable.