There are many ways to spin a photon: Half-quantization of a total optical angular momentum

Abstract

The angular momentum of light plays an important role inmany areas, from optical trapping to quantum information. In the usual three-dimensional setting, the angularmomentum quantum numbers of the photon are integers, in units of the Planck constant h.We show that, in reduced dimensions, photons can have a half-integer total angularmomentum. We identify a new form of total angular momentum, carried by beams of light, comprising an unequal mixture of spin and orbital contributions.We demonstrate the half-integer quantization of this total angular momentum using noise measurements. We conclude that for light, as is known for electrons, reduced dimensionality allows new forms of quantization.