Observation of quantum entanglement in top-quark pairs using the ATLAS detector

Abstract

Entanglement is a key feature of quantum mechanics, with applications in fields such as metrology, cryptography, quantum information, and quantum computation. It has been observed in a wide variety of systems and length scales, ranging from the microscopic to the macroscopic. However, entanglement remains largely unexplored at the highest accessible energy scales. Here we report the highest-energy observation of entanglement, in top$-$antitop quark events produced at the Large Hadron Collider, using a proton$-$proton collision dataset with a center-of-mass energy of $\sqrt{s}=13$ TeV and an integrated luminosity of 140 fb${}^{-1}$ recorded with the ATLAS experiment. Spin entanglement is detected from the measurement of a single observable $D$, inferred from the angle between the charged leptons in their parent top- and antitop-quark rest frames. The observable is measured in a narrow interval around the top$-$antitop quark production threshold, where the entanglement detection is expected to be significant. It is reported in a fiducial phase space defined with stable particles to minimize the uncertainties that stem from limitations of the Monte Carlo event generators and the parton shower model in modeling top-quark pair production. The entanglement marker is measured to be $D=-0.537\pm 0.002\text{(stat.)}\pm 0.019\text{(syst.)}$ for $340<m_{t\bar{t}}<380$ GeV. The observed result is more than five standard deviations from a scenario without entanglement and constitutes the first observation of entanglement in a pair of quarks and the highest-energy observation of entanglement so far.

49 pages in total, author list starting page 32, 4 figures, 2 tables, published as Nature 633 (2024) 542. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2021-24

References in corpus (18)

• The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations
• An Introduction to PYTHIA 8.2
• Parton distributions for the LHC
• Matching NLO QCD computations with Parton Shower simulations: the POWHEG method
• Herwig++ Physics and Manual
• A parton shower algorithm based on Catani-Seymour dipole factorisation
• Pileup subtraction using jet areas
• Single-top Wt-channel production matched with parton showers using the POWHEG method
• Two-loop soft anomalous dimensions for single top quark associated production with a W- or H-
• Automatic spin-entangled decays of heavy resonances in Monte Carlo simulations
• Single-top hadroproduction in association with a W boson
• The Catchment Area of Jets
• Higgs boson production in association with top quarks in the POWHEG BOX
• Demonstration of entanglement-by-measurement of solid state qubits
• An NLO+PS generator for $t\bar{t}$ and $Wt$ production and decay including non-resonant and interference effects
• Top-quark pair production near threshold at LHC
• Measurement of Spin Correlation in Top-Antitop Quark Events and Search for Top Squark Pair Production in pp Collisions at $\sqrt{s}=8$ TeV Using the ATLAS Detector
• A unified approach to entanglement criteria using the Cauchy-Schwarz and Hölder inequalities

Cited by in corpus (41)

• Observation of quantum entanglement in top quark pair production in proton-proton collisions at $\sqrt{s}$ = 13 TeV
• Measurements of polarization and spin correlation and observation of entanglement in top quark pairs using lepton+jets events from proton-proton collisions at $\sqrt{s}$ = 13 TeV
• Observation of a pseudoscalar excess at the top quark pair production threshold
• Quantum Information meets High-Energy Physics: Input to the update of the European Strategy for Particle Physics
• Optimizing Entanglement and Bell Inequality Violation in Top Anti-Top Events
• Quantum simulation of entanglement and hadronization in jet production: lessons from the massive Schwinger model
• Entanglement and Bell nonlocality with bottom-quark pairs at hadron colliders
• Measuring spin correlation between quarks during QCD confinement
• Entanglement and Bell inequality violation in vector diboson systems produced in decays of spin-0 particles
• Quantum Tomography at Colliders: With or Without Decays
• Toponium: the smallest bound state and simplest hadron in quantum mechanics
• Interference Resurrection of the $\tau$ Dipole through Quantum Tomography
• Climbing to the Top of the ATLAS 13 TeV data
• Probing Quantum Phenomena through Photoproduction in Relativistic Heavy-Ion Collisions
• 1 Particle - 1 Qubit: Particle Physics Data Encoding for Quantum Machine Learning
• Testing spooky action between free-traveling electron-positron pairs
• Experimental Review of the Quarkonium Physics at the LHC
• Universality of entanglement in gluon dynamics
• Probing and Knocking with Muons
• Quantum state tomography with muons
• The Magic Barrier before Thermalization
• Probing Spin and Lifetime Correlations in Entangled Hyperon-AntiHyperon Pairs
• Statistical Indications of Toponium Formation in Top Quark Pair Production
• Entanglement and magic on the light-front
• Sensitivity Analysis of the Top-Quark Sector
• Experimental characterization of the hierarchy of quantum correlations in top quark pairs
• Characterization of the quantum state of top quark pairs produced in proton-proton collisions at $\sqrt{s}$ = 13 TeV using the beam and helicity bases
• Nonlocal Advantage of Quantum Coherence in Top Quarks
• From top quarks to enhanced quantum key distribution: A Framework for Optimal Predictability of Quantum Observables
• TOP2024: an overview of experimental results
• Further Evidence for Near-Tsirelson Bell-CHSH Violations in Quantum Field Theory via Haar Wavelets
• Genuine tripartite entanglement in Bhabha scattering with an entangled spectator particle
• Simulating Bell inequalities with Qibo
• Top quark spin and quantum entanglement in the ATLAS experiment
• Study $\gamma \gamma \to {\tau }^{+}{\tau }^{-}$ process including ${\tau }^{+}{\tau }^{-}$ spin information in Pb-Pb ultraperipheral collision and at Lepton collider
• Gauge and diffeomorphism invariance from quantum information principles
• Parameter Inference from Final-State Entanglement in Higgs Decays
• Single-spin measurements and heavy new physics in the $e^{+}{e}^{-}\to t\bar{t}$ process at an FCC-ee
• Gedanken Experiments of Entanglement in Particle Physics: Interactions, Operators and Bell Inequalities in Flavor Space
• Global $\Lambda$ hyperon polarization in low-energy heavy ion collisions -- a scenario without vorticity
• Unitarity constrains the quantum information metrics for particle interactions