When light hits your eyeball, the spinning photons actually twist it (infinitesimally). The force of that spin, known as angular momentum, has always been thought to be a direct multiple of a quantum physics number called Planck's constant. However, scientists from Trinity College Dublin discovered a form of light with an angular momentum that's exactly half that amount. Though that may not sound like a big deal, the discovery could have "real impact on the study of light waves in areas such as secure optical communications," says Professor John Donegan.
The team devised an experiment to effectively reduce the number of dimensions that the light operates in. First, they passed the light through a crystal, turning the beam into a hollow cylinder with a "screw-like structure." Then, they built a device that measures angular momentum when the light passes through the crystal and also when it bypasses it. In the latter case, the spin was an exact multiple of Planck's constant, as expected, but when it passed through the crystal, the angular momentum shifted by one-half.
What I think is so exciting about this result is that even this fundamental property of light, that physicists have always thought was fixed, can be changed.
The result isn't completely unexpected, as scientists have long theorized that fractional angular momentum in photons is possible in certain instances. However, this is the first time experiments have proved the results -- much like how scientists recently proved that theoretical gravitational waves are a real thing. Practically, engineers could exploit the finding to create faster and more secure forms of data transmission. More importantly, the discovery represents a true breakthrough in quantum mechanics if it stands up. "What I think is so exciting about this result is that even this fundamental property of light, that physicists have always thought was fixed, can be changed," says lead researcher Paul Eastham.