Physicists have observed quantum entanglement between pairs of top quarks produced in high-energy collisions at the Large Hadron Collider (LHC) at CERN. This marks the first time entanglement has been detected in a pair of quarks and the highest energy at which entanglement has been observed to date. Top quarks are the heaviest known fundamental particles.
They normally decay into other particles before they have time to combine with other quarks. In the process, they transfer their spin and other quantum properties to their decay products. To detect entanglement, researchers from the ATLAS and CMS collaborations analyzed data from proton-proton collisions that occurred at an energy of 13 teraelectronvolts (TeV) during the LHC’s second run between 2015 and 2018.
They specifically looked for pairs of top quarks produced with low momentum relative to each other, where the spins of the two quarks are expected to be strongly entangled.
cern observes top quarks entanglement
The degree of spin entanglement was inferred from the angle between the directions in which the electrically charged decay products of the two quarks were emitted.
After measuring these angular separations and correcting for experimental effects, both the ATLAS and CMS teams observed spin entanglement between top quarks with a statistical significance larger than expected if there was no entanglement. The CMS collaboration also found entanglement in pairs of top quarks produced with high momentum relative to each other. In this case, the relative positions and timing of the two top quark decays excluded the possibility of classical information exchange between them at the speed of light or slower.
“While particle physics is deeply rooted in quantum mechanics, the observation of quantum entanglement in a new particle system and at much higher energy than previously possible is remarkable,” said ATLAS spokesperson Andreas Hoecker. It paves the way for new investigations into this fascinating phenomenon.
CMS spokesperson Patricia McBride added, “With measurements of entanglement and other quantum concepts in a new particle system and at an energy range beyond what was previously accessible, we can test the boundaries of particle physics in new ways and look for signs of new physics that may lie beyond it.
This groundbreaking observation demonstrates the potential of using high-energy particle colliders like the LHC as tools for testing our fundamental understanding of quantum mechanics. It opens up new possibilities for exploring relativistic quantum effects and other foundational problems in quantum physics at the highest energies currently accessible.
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