Fig. 1: Schematic setup.

Monochromatized neutrons, with polarization vector parallel to the direction of propagation (+y), enter the interferometer. Inside the interferometer the rotating field generator (RFG) creates a magnetic field \({\overrightarrow{B}}_{{\rm{RFG}}}(\Omega ,t)\) in path I, rotating in a plane perpendicular to the neutron beam. After recombination at the last interferometer plate, the neutrons in forward direction (O-beam) are detected in a ³He counter tube. Spin directions are indicated with blue arrows, the magnetic field in violet. The phase shifter plate consists of a slab of sapphire and is rotated to record interferograms by inducing relative phase shifts \(\chi\) between the paths. A polarizing supermirror can be placed in the forward beam for spin analysis.