Dr. Allen Scheie

Postdoctoral Research Associate

Oak Ridge National Laboratory

Neutron Scattering Division

Title: Witnessing entanglement in quantum magnets using neutron scattering

Abstract: In this talk I show how information about solid state quantum entanglement can be extracted from magnetic neutron scattering using model-independent techniques. Using the 1D spin chain KCuF3, we examine three entanglement witnesses applicable to neutron scattering: one tangle, two tangle, and Quantum Fisher Information (QFI). We find that QFI is the most experimentally robust, giving good agreement between theory and experiment over all measured temperatures, and witnessing multipartite entanglement up to 75 K. We then apply the entanglement witnesses to the 2D triangular lattice KYbSe2, showing the presence of appreciable entanglement in the low temperature phase. We then use diffuse scattering fits, heat capacity comparisons, and nonlinear spin wave fits to demonstrate that KYbSe2 is proximate to a quantum spin liquid. We thus provide a rigorous route to studying and understanding highly entangled quantum phases.