Physicists discover a new form of light

Scientists from the CRANN Institute at Trinity College and the School of Physics at Trinity College Dublin have found a new kind of light that will change our perception of the basic properties of light.

Angle of momentum is one of the quantifiable properties of a light beam. Up until now, it was believed that the angular momentum in all light types would be a multiple of Planck's constant, which is the physical constant that establishes the range of quantum effects.

Recently, Kyle Ballantine, a recent PhD graduate, and Professor Paul Eastham from the School of Physics at Trinity College Dublin, along with Professor John Donegan from CRANN, have shown how to create a new type of light in which each photon—a particle that makes up visible light—takes only half of this value for its angular momentum. Despite being little, this change is significant. Science Advances, an online publication, reported these findings lately.

Assistant Professor Paul Eastham made the following statement about their research: "We want to know how light behaves and whether that may be beneficial. This finding excites me much because it shows that even a basic characteristic of light—one that physicists have long believed to be unchangeable—can be altered.

"My research focuses on nanophotonics, which is the study of light behavior on the nanometer scale," stated Professor John Donegan. A light beam's color or wavelength and the less well-known concept of angular momentum define it. The amount that anything rotates is measured by its angular momentum. A light beam may rotate about its own axis in addition to moving in a straight path. Thus, each photon that enters your eye in the morning from the mirror causes a little rotation of your pupil."

The study of light waves will be significantly impacted by our discoveries in fields like secure optical communications.

"The topic of light has always been one of interest to physicists, while also being documented as one of the areas of physics that is best understood," stated CRANN Director Professor Stefano Sanvito. This finding is revolutionary for both science and the field of physics. It pleases me to see that Trinity's Physics Department and CRANN are once again conducting important scientific studies that complicate our knowledge of light."

The research team employed an effect that was found in the same university about 200 years prior to accomplish this finding. Mathematician William Rowan Hamilton and physicist Humphrey Lloyd discovered in the 1830s that a light beam transformed into a hollow cylinder as it passed through specific crystals. The scientists produced light beams with a screw-like structure by utilizing this phenomena.

They designed an experiment to verify their prediction that the photon's angular momentum would be half an integer by analyzing these beams using the framework of quantum mechanics. By use of a specifically designed apparatus, they managed to gauge the angular momentum flux within a light beam. Additionally, they were able to quantify the fluctuations in this flow brought about by quantum phenomena for the first time. The results of the experiments showed that the angular momentum of each photon shifted slightly—by half of Planck's constant.

In just two of the three dimensions of space, theoretical physicists have conjectured since the 1980s about the workings of quantum mechanics for particles that are free to travel. It was found that this would open up weird new possibilities, such as particles with quantum numbers that were fractions of what was predicted. For the first time, our work demonstrates that these theories are possible to realize using light.