Measurement of the Berry phase with polarized neutrons

Abstract

When a quantum mechanical system is transported adiabatically around a closed circuit in parameter space, the system will, in addition to the usual dynamical phase, pick up a “topological”phase which depends only on the geometric history of the system. This phase, which is named after Berry who predicted it in 1984, has a number of exciting properties. We have measured these phases in neutron spin-rotation in helical magnetic fields.