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arXiv:2602.21311

Coherent Quantum Evaluation of Collider Amplitudes for Effective Field Theory Constraints

Yacine Haddad, Kaidi Xu, Vincent Croft, Jad C. Halimeh, Michele Grossi

hep-phhep-exquant-phSubmitted Feb 24, 2026• Announced Feb 26, 2026• 0 citations
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Abstract

Precision measurements at electron-positron colliders provide stringent tests of the Standard Model and powerful probes of possible higher-dimensional interactions. We present a hybrid quantum-classical framework for computing leading-order helicity amplitudes for $e^+e^-\to \ell^+\ell^-$ scattering on gate-based quantum hardware and using the resulting cross sections to constrain both Standard Model couplings and effective field theory operators. In our approach, external kinematics are encoded into single-qubit Weyl spinors, and full helicity amplitudes are reconstructed by coherently combining diagrammatic contributions within a single quantum circuit. Classical post-processing yields physical amplitudes and differential cross sections that can be directly compared with collider data. As a proof of concept, we compute unpolarised angular distributions and perform binned likelihood fits to precision electron-positron measurements. The extracted bounds are statistically consistent with Standard Model expectations, demonstrating that quantum-assisted amplitude evaluation can interface directly with phenomenological analyses and experimental data. This work establishes a concrete pathway toward applying quantum computing to precision collider physics and effective field theory studies.

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We investigate the quantum properties of heavy-fermion pairs, such as ttˉt\bar tttˉ or τ+τ−τ^+τ^-τ+τ−, produced in lepton-lepton collisions with polarised beams. Focusing on spin correlations, entanglement, Bell-inequality violation, and quantum-information-theoretic measures such as purity and magic, we analyse how beam polarisation shapes the structure of the spin-density matrix. We derive analytic expressions for a wide range of helicity configurations, including both Standard Model contributions and generic new-physics effects parametrised by scalar, vector, and tensor four-fermion operators within an effective field theory framework. We show that beam polarisation unlocks a substantially richer set of spin configurations and significantly enhances sensitivity to non-standard interactions. As a phenomenological application, we study ttˉt\bar tttˉ production at a future linear collider and demonstrate that quantum observables provide a comprehensive and complementary probe of top-quark interactions and stronger constraints on the scale of new physics.
We probe the possibilities of efficiently constructing simple Feynman diagrams into quantum devices. More precisely, we study Drell-Yan lepton pair creation at the partonic level of the form q qbar -> gamma/Z -> l- l+. We develop quantum gates that build up the relevant diagrams using simple Feynman rules, such as vertex and propagator gates V and P. We show how the quantum circuit may compute simultaneous amplitudes in the phase space and how to reach the full integrated cross section from the outputs. In addition to this, we also show how the circuit is able to simultaneously isolate the interference effects of the contributing diagrams by a simple basis rotation. The circuit design is made to be general, and thus this work constitutes a step towards the implementation of arbitrary scattering process computations and efficient interference analyses.
A bstract We investigate the quantum properties of heavy-fermion pairs, such as tt‾ t\overline{t} tt t t ¯ or τ + τ − , produced in lepton-lepton collisions with polarised beams. Focusing on spin correlations, entanglement, Bell-inequality violation, and quantum-information-theoretic measures such as purity and magic, we analyse how beam polarisation shapes the structure of the spin-density matrix. We derive analytic expressions for a wide range of helicity configurations, including both Standard Model contributions and generic new physics effects parametrised by scalar, vector, and tensor four-fermion operators within an effective field theory framework. We show that beam polarisation unlocks a substantially richer set of spin configurations and significantly enhances sensitivity to non-standard interactions. As a phenomenological application, we study tt‾ t\overline{t} tt t t ¯ production at a future linear collider and demonstrate that quantum observables provide a comprehensive and complementary probe of top-quark interactions and stronger constraints on the scale of new physics.
We formulate collider observables based on quantum steering ellipsoids (QSEs) for reconstructed bipartite systems of spin-1/21/21/2 particles. A collider spin density matrix defines a two-qubit state, while its QSE gives the geometry of conditional states accessible through local measurements. This makes the ellipsoid a direct probe of the quantum properties of fundamental particles, encoding polarization, spin correlation anisotropy, accessible-state volume, and the orientation of the dominant correlation axes. Using top-quark pair production as a benchmark process, we show how QSE observables organize the Standard Model spin state, probe entanglement, steerability, and Bell-nonlocality criteria, and use an expected precision metric to assess sensitivity to non-local correlations in the boosted central region. We show that different dimension-six operators generate distinctive QSE deformations, and provide a geometric interpretation of quantum information observables in high-energy particle physics. Quantum steering geometry therefore provides a unified framework for particle collider tomography, quantum information diagnostics, and precision searches for physics beyond the Standard Model with applications spanning the HL--LHC and future lepton, muon, flavor, and electron-ion collider programs.