Abstract: Neutron interferometry is practiced with de Broglie wavelengths of 0.1 nanometer over path lengths of 0.1 meter, typically in Mach-Zehnder configurations familiar to practitioners of atom and optical interferometry. However, since ordinary matter is largely transparent to neutrons, their interference can be manifested deep within materials. Neutrons undergoing Bragg diffraction experience a type of oscillation inside a crystal known as pendellösung interference [1] which results in a modulation of the forward-diffracted and Bragg-reflected intensities. This phenomenon allows for the precise determination of the neutron-silicon structure factor. Knowing the structure factor at several Bragg conditions strongly constraints possible atomic length scale interactions; aka a "fifth" force. In addition, structure factor measurements probe the structure of the neutron via the neutron charge radius and provide information on thermal motion of the atoms in a lattice.
[1] "Pendellösung interferometry probes the neutron charge radius, lattice dynamics, and fifth forces," B. Heacock, et al., Science 373, 1239 (2021)
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