Intrinsic Orbital Angular Momentum States of Neutrons
Ronald L. Cappelletti, Terrence J Jach, John T. Vinson
A recent neutron interferometry experiment attempted to observe the orbital angular momentum (OAM) of neutron de Broglie waves of neutron de Broglie waves using a spiral phase (SPP) (Nature 525, 504 (2015) ). Based upon conventional neutron optical ideas, we provide an alternative explanation of the two-dimensional interference patterns observed. Since the transverse coherence length of the neutrons in the NIST interferometer is a very small fraction of the transverse dimension of the SPP used, we show that neutron wave packets passing through the SPP acquire a vanishingly small intrinsic OAM. Given the small transverse coherence of the incident neutrons, we show that the LLL perfect silicon crystal neutron interferometer actually consists of a very large number of independent, incoherently superposed interferometers. Simple phase contrast explains the observed interference patterns.