Interference of neutron beams of orthogonal spin state

Spin superposition is a special case of the quantum mechanical principle of linear superposition of states. Experiments are reported, which demonstrate this special case for thermal neutrons in an explicit way. A polarized monochromatic neutron beam was spatially separated into two coherent partial beams by a single crystal interferometer. Using Larmor precession in a well defined static magnetic field, the polarization vector of one partial beam could be inverted by a rotation of 180deg. Then the partial beams were superposed. Behind the interferometer the polarization vector of the forward beam should lie within the plane normal to the initial polarization directions and it should be possible to turn it within this plane by a scalar phase shift in between the two partial beams. This effect was observed by means of three dimensional polarization analysis. The quantum mechanical description of the experiment and the experimental results were in good agreement within the achievable accuracy. Aside from the actual interference experiments, measurements of the polarization of the incident beam and of the partial beams within the interferometer as well as the consequences arising from a change of wave length due to polarization inversion in a static magnetic field are considered. Finally a possible alternative to the spin superposition experiment is investigated in which a high frequency coil is used to invert the polarization vector of one partial beam. (Author)