Three-beam interference and which-way information in neutron interferometry

Abstract

A two-loop perfect-crystal neutron interferometer was used for the quantitative determination of which-way (WW) information and the verification of the duality relation between predictability and visibility. Our interferometer has two remarkable features, it allows the absorption-free tuning of WW information and it enables the simultaneous measurement of the duality relation without changing the interferometer setup. In addition, the duality relation of three interfering beams is a good demonstration that WW information should not be misused as particle property because one interferometer beam remains in a coherent superposition of two path alternatives, which is not consistent with the particle picture. The coherent WW tuning was performed without changing the neutron's momentum and without dephasing.