A new perspective on the complex world of quantum physics

At the CERN research center in Geneva, international scientists are investigating the properties and interactions of elementary particles, among other things, in order to solve previously unanswered questions in physics. Protons are accelerated and collided at the world's most powerful particle accelerator, the Large Hadron Collider (LHC). This produces billions of elementary particles, whose tracks and decay are recorded by large detectors. One such detector is the ATLAS experiment, in which Prof. Kevin Kröninger's team at TU Dortmund University is also involved.

Until now, quantum entanglement at the high energies available at the LHC has been largely unexplored. With their current measurements, the ATLAS collaboration is now making an important contribution to further understanding the phenomenon: the researchers were able to observe quantum entanglement between a top quark and its antimatter counterpart for the first time. Top quarks regularly pose challenges for scientists, as a top quark normally decays into other particles before it has time to combine with other quarks. Physicists therefore observe these decay products and use them to deduce the quantum properties of the top quark. To observe the entanglement between top quarks, the ATLAS team used data from proton-proton collisions that took place at the LHC between 2015 and 2018 at an energy of 13 teraelectronvolts.

Dr. Andrea Knue from TU Dortmund University was also involved in this measurement. She is a member of Prof. Kevin Kröninger's working group and has also led the ATLAS experiment's top quark research group for two years, in which around 300 scientists from all over the world work together. In her research, Dr. Knue investigates top quark properties and her work has helped to improve the understanding of so-called signal modeling, which had a major influence on the precision of the measurement now presented in Nature. The current findings on quantum entanglement of top quarks have since been confirmed by two further observations by scientists at the CMS detector at CERN.