Dr. Roger Pynn, Indiana University Bloomington

Title: What are Entangled Neutrons, Anyway?

Abstract: For more than 75 years, neutron scattering has been a powerful tool for probing the positions 
and dynamics of atoms, as well as the magnetic fields that shape material properties. In 
parallel, advances in light optics have increasingly harnessed the quantized nature of photons 
to achieve higher precision and uncover new phenomena. Can similar quantum ideas be 
applied to neutrons? Remarkably, the spin, momentum, and energy of individual neutrons can 
indeed be placed into entangled, Bell-like states. In this talk, I will describe how such 
entanglement has been realized experimentally, and how we validated its existence.
The challenge now is to exploit these mode-entangled neutrons to access new forms of 
information. Recent theoretical work suggests that entangled neutrons could uniquely probe 
electron spin entanglement in specific systems—though experimental confirmation remains to 
be achieved. Still, entanglement has already enabled measurements that would have been 
impossible otherwise. As one example, I will present the first observation of a giant Goos–
Hänchen effect for matter waves and indicate prospects for applying similar techniques to 
materials of scientific and technological relevance. Looking forward, these methods will be 
especially valuable at the next-generation neutron source now being planned at Oak Ridge 
National Laboratory.