Wigner function and coherence properties of cold and thermal neutrons

We analyze the coherence properties of a cold or a thermal neutron by utilizing the Wigner quasi distribution function. We look in particular at a recent experiment performed by Badurek et al., in which a polarized neutron crosses a magnetic field that is orthogonal to its spin, producing highly non-classical states. The quantal coherence is extremely sensitive to the field fluctuation at high neutron momenta. A 'decoherence parameter' is introduced in order to get quantitative estimates of the losses of coherence. (Authors)