Nuclear physics: Neutrons with a twist.

Abstract

Neutrons do not normally have orbital angular momentum. But the demonstration that a beam of neutrons can acquire this property, 23 years after it was shown in photons, offers the promise of improved imaging technologies. See Letter p.504 Orbital angular momentum is a quantized degree of freedom exploited in many applications. The photon orbital angular momentum has been used in fundamental tests of quantum mechanics and imaging and the electron orbital angular momentum has proven useful for determining the chirality of crystals. But the phenomenon had not previously been demonstrated in neutrons. Here Dmitry Pushin and colleagues show how to control orbital angular momentum states in a neutron beam through the use of macroscopic spiral phase plates. After applying this 'twist' to an input neutron beam, the quantized orbital angular momentum of neutrons is characterized by neutron interferometry. In contrast to photons and electrons, neutrons are massive particles, hence this result could open important new perspectives for testing quantum mechanics with massive observables. In addition, the neutron orbital angular momentum could enable new approaches for neutron scattering techniques.