Orbital Angular Momentum of Photons
MEASURING THE ORBITAL ANGULAR MOMENTUM OF SINGLE PHOTONS
http://www.physics.gla.ac.uk/Optics/projects/singlePhotonOAM/ and this one from Phys Rev Letters:
http://optics.org/articles/news/8/6/14/1 Single photons show momentum state
18 June 2002
An optical technique reveals the orbital angular momentum state of single photons for the first time.
A new technique that measures the orbital - rather than the spin - angular momentum of single photons could lead to the development of super-efficient quantum communication systems. Previously, physicists had only been able to measure this quantity for many photons in a beam, or detect a certain value of it for single photons. But the set-up devised by Johannes Courtial of the University of Glasgow and colleagues should be able to reveal any orbital angular momentum state of a single photon (Phys. Rev. Lett. 88 257901).