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The trace distance between density matrices, a nifty tool in new-physics searches

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arxiv 2501.03311 v2 pith:EUGEWEQE submitted 2025-01-06 hep-ph hep-exquant-ph

classification hep-phhep-exquant-ph
keywords quantuminformationdistancephysicsfirstothersearchestrace
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abstract

Quantum information methods have been brought to bear on high-energy physics, including the study of entanglement and Bell nonlocality in collider experiments. Quantum information observables have also been employed to constrain possible new physics effects. We improve on this point by introducing quantum information tools routinely used to compare quantum states: the trace distance and the fidelity. We find that the former outperforms other quantum information observables considered in the literature and, together with the cross section, yields the strongest bounds on possible departures from the Standard Model. The power of the proposed methodology is demonstrated with three examples of new physics searches. The first concerns the chromomagnetic dipole moment of the top quark and yields the first bound computed by means of quantum tomography and actual experimental data. The other two examples use Monte Carlo simulations and set the projected limits on the anomalous couplings of the $\tau$ leptons at Belle and at a future collider, which is taken to be LEP3. For these new physics searches we also compare the sensitivity of the trace distance to those of other quantum information quantities like concurrence, magic, and the fidelity distance. In passing, we provide the first determinations of magic in colliders data by analyzing the top-quark pair production at the LHC and the charmonium decays. The significance is well above the $5\sigma$ level in both the cases.

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Cited by 5 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Qubit-qubit-qutrit quantum correlations in $H \to f \bar f V$

    quant-ph 2026-07 conditional novelty 7.0 of 10

    In h→τ^-τ^+ Z decays, the spin state is genuinely qubit-qubit-qutrit entangled almost everywhere, violates Bell inequalities throughout, and carries up to 1.95 bits of non-local magic.

  2. High Energy Photon Polarimetry at Lepton Colliders: Quantum Information from Converted Photons

    hep-ph 2026-07 conditional novelty 6.5 of 10

    Converted photons in Belle II enable high-significance measurements of Bell nonlocality, discord, concurrence, magic and steerability for macroscopically separated GeV diphotons, provided opening-angle resolution reac...

  3. Hadron Structure from the Hierarchy of Quantum Correlations in Deep-Inelastic Scattering

    hep-ph 2026-07 conditional novelty 6.0 of 10

    Quantum-information measures of the DIS final electron-quark state are shown to be sensitive to transversity PDFs and can discriminate between different tensor-charge extractions.

  4. Entanglement, Yang-Mills, and the Scattering Matrix as an SU(N)-equivariant Kernel

    hep-ph 2025-11 conditional novelty 6.0 of 10

    SU(N) symmetry fixes the entangling power of 2→2 scattering: Yang-Mills adjoint scattering has a group-only entanglement maximum at 90° (3/4 for SU(2), ≈0.91 for SU(3)), and maximal-entanglement preservation selects t...

  5. Spin versus Magic: Lessons from Gluon and Graviton Scattering

    hep-th 2025-08 accept novelty 6.0 of 10

    For 2 to 2 scattering of massless spin-1/2 to spin-2 particles, the averaged generated magic decreases monotonically with spin, with maxima well below the two-qubit upper bound.

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