Phys.org November 8, 2021
The lack of methods to experimentally detect and quantify entanglement in quantum matter impedes our ability to identify materials hosting highly entangled phases, such as quantum spin liquids. An international team of researchers (USA – Oak Ridge National Laboratory, Drew School, Germany, UK, France, Poland) tested three entanglement witnesses using a combination of neutron scattering experiments and computational simulations. Entanglement witnesses are techniques that act as data analysis tools to determine which spins cross the threshold between the classical and quantum realms. To ensure that the witnesses could be trusted, the team applied all three of them to a material they knew to be entangled because of a previous spin dynamics study. Two of the witnesses adequately indicated the presence of entanglement in this one-dimensional spin chain but the third, which is based on quantum information theory, fared exceptionally well at the same task. The quantum Fisher information, or QFI, witness showed a close overlap between theory and experiment, which makes it a robust and reliable way to quantify entanglement. The results lay the foundation for a general entanglement detection protocol for quantum spin systems…read more. TECHNICAL ARTICLE  1 , 2Â
…This gage allows the researchers to distinguish between classical and quantum spin fluctuations. Credit: Nathan Armistead/ORNL, U.S. Dept. of Energy