Observation of quantum entanglement with top quarks at the ATLAS detector.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 39294352.
- Also identified by DOI 10.1038/s41586-024-07824-z and PMC identifier 11410654.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Entanglement is a key feature of quantum mechanics<sup>1-3</sup>, with applications in fields such as metrology, cryptography, quantum information and quantum computation<sup>4-8</sup>. It has been observed in a wide variety of systems and length scales, ranging from the microscopic<sup>9-13</sup> to the macroscopic<sup>14-16</sup>. 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 centre-of-mass energy of √s = 13 TeV and an integrated luminosity of 140 inverse femtobarns (fb)<sup>-1</sup> 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, at which 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 the limitations of the Monte Carlo event generators and the parton shower model in modelling top-quark pair production. The entanglement marker is measured to be D = -0.537 ± 0.002 (stat.) ± 0.019 (syst.) for <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>340</mn> <mspace></mspace> <mi>GeV</mi> <mo><</mo> <msub><mrow><mi>m</mi></mrow> <mrow><mi>t</mi> <mover><mrow><mi>t</mi></mrow> <mo>¯</mo></mover> </mrow> </msub> <mo><</mo> <mn>380</mn> <mspace></mspace> <mi>GeV</mi></mrow> </math> . The observed result is more than five standard deviations from a scenario without entanglement and hence constitutes the first observation of entanglement in a pair of quarks and the highest-energy observation of entanglement so far.