Observation of 4π-symmetry of the neutron wave function under space rotation

Abstract

We observed 4π-symmetry of the neutron wave function under rotation in space produced by slowly rotating an adiabatic guide field. In contrast to all previous works, the present experiment is of purely topological nature, i.e. it does not involve the Larmor precession and the result depends only on the topology and not on the value of the magnetic field and the neutron magnetic moment. This is the first experimental observation which cannot be explained by simply applying the common concept of wave optical dynamic phase, consistently with the Stern–Gerlach spin quantization, to each of the “spin-up” and “spin-down” energy eigenstates superposed in the neutron wave function.