Observation of polarized neutron interference in spin space

The coherent superposition of particle quantum states resulting from differ ent spatial paths shows well-known interference effects. Another type of in terference is Larmor precession, which can be described as neutron wave int erference in spin space, i.e. interference on the same spatial path. Here w e show several new manifestations of interference phenomena of the latter t ype. The interference is produced by coherent population of different I-z = +/- 1/2 spin states in a polarized neutron beam between two resonant radio -frequency (RF) spin flippers. Their spin hip probability, and thus the occ upation numbers of the spin states, can be tuned between 0 and 1 by changin g the RF amplitude. This leads to interference effects in the polarization since the energy exchanged between the RF field and spin yields different p hase evolution in the spatial parts of the neutron states. Depending on the preparation of the initial neutron states, five values for the time-indepe ndent phase difference between the final neutron states can be observed.