Experimental evidence for the two-path description of neutron spin echo

Journal article (2024)

Authors

S. McKay Indiana University - Purdue University
A. A.M. Irfan Indiana University - Purdue University
Q. Le Thien Indiana University - Purdue University
N. Geerits Technische Universität Wien
S.R. Parnell RID/TS/Instrumenten groep
Robert M. Dalgliesh Rutherford Appleton Laboratory
N. V. Lavrik Oak Ridge National Laboratory
I. I. Kravchenko Oak Ridge National Laboratory
G. Ortiz University of Waterloo, Indiana University - Purdue University
R. Pynn Oak Ridge National Laboratory, Indiana University - Purdue University
Research Group
RID/TS/Instrumenten groep
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Published Date

2024

Language

English

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Research Group

RID/TS/Instrumenten groep

Abstract

We describe an experiment that strongly supports a two-path interferometric model in which the spin-up and spin-down components of each neutron propagate coherently along spatially separated parallel paths in a typical neutron spin-echo small-angle scattering (SESANS) experiment. Specifically, we show that the usual semi-classical, single-path treatment of Larmor precession of a polarized neutron in an external magnetic field predicts a damping as a function of the spin-echo length of the SESANS signal obtained with a periodic phase grating when the transverse width of the neutron wave packet is finite. However, no such damping is observed experimentally, implying either that the Larmor model is incorrect or that the transverse extent of the wave packet is very large. In contrast, we demonstrate theoretically that a quantum-mechanical interferometric model in which the two mode-entangled (i.e., intraparticle entangled) spin states of a single neutron are separated in space when they interact with the grating accurately predicts the measured SESANS signal, which is independent of the wave packet width.