The European Organization for Nuclear Research (CERN) has announced a significant breakthrough in quantum physics. Researchers at CERN's Large Hadron Collider (LHC) have observed quantum entanglement between fundamental particles known as top quarks at unprecedented energy levels. The findings were published today in Nature.
Quantum entanglement, a phenomenon where the state of one particle is intrinsically linked to another regardless of distance, has been extensively studied in various systems. It gained notable recognition when Alain Aspect, John F. Clauser, and Anton Zeilinger received the Nobel Prize in Physics in 2022 for their work with entangled photons, confirming predictions by the late CERN theorist John Bell.
However, until now, entanglement at the high energies produced by particle colliders like the LHC remained largely unexplored. The ATLAS collaboration at CERN first reported this observation in September 2023, which has since been corroborated by two observations from the CMS collaboration.
"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," stated Andreas Hoecker, spokesperson for ATLAS. "It paves the way for new investigations into this fascinating phenomenon, opening up a rich menu of exploration as our data samples continue to grow."
The ATLAS and CMS teams focused on observing quantum entanglement between top quarks and their antimatter counterparts using proton-proton collision data from the LHC's second run (2015-2018). These collisions occurred at an energy level of 13 teraelectronvolts. They specifically analyzed pairs of top quarks produced with low relative momentum to each other, where strong spin entanglement was expected.
Physicists inferred the presence and degree of spin entanglement by examining the angles between electrically charged decay products emitted by the quarks. Both teams measured these angular separations and adjusted for experimental factors that might affect results. Their findings revealed spin entanglement between top quarks with statistical significance exceeding five standard deviations.