Go and catch a falling neutron… Available to Purchase

A team of experimenters has used a neutron interferometer to observe the quantum‐mechanical phase shift of neutrons caused by their interaction with the Earth's gravitational field. The experiment is one of the first (if not the first) observations of the principle of equivalence for a quantum‐mechanical system. The experimenters, who reported their work in Phys. Rev. Letters on 9 June, are Roberto Colella and Albert W. Overhauser (Purdue University) and Samuel A. Werner (Ford Motor Company).