Photons can have half-integer angular momentum
DOI: 10.1063/PT.5.029831
Gizmodo : Aside from their wavelength, photons also have a measurable angular momentum that characterizes their rotation along their axis of travel. That value has always been observed to be some integer multiple of Planck’s constant. Now Paul Eastham of Trinity College Dublin and his colleagues have manipulated photons so they have half-integer angular momentum. To do that, the researchers made use of a phenomenon first discovered in the 1830s: When light is passed through certain crystals, it creates a cylinder-like structure. Theoretical analysis of the system suggested that the resulting photons had half-integer angular momentum, and measurements proved the predictions correct. The team thinks that such photons could be used for encrypted light-based communications.
