In a breakthrough that has the potential to alter our understanding of the fundamental nature of light, scientists from the Trinity College Dublin School of Physics and the CRANN Institute in Ireland have discovered a never before seen new form of luminescence.
Previously, it was believed angular momentum, a vector quantity which expresses the amount of dynamical rotation present in a beam of light, would always be a multiple of Planck’s constant (a physical constant which sets the scale of quantum effects), regardless of the light’s form.
However, in a new paper published in a recent edition of the journal Science Advances, Trinity College PhD graduate Kyle Ballantine, Professor Paul Eastham and their colleagues reported that they had demonstrated a new type of light where the angular momentum of each particle takes on only half of this value – a small but profound difference, according to the study authors.
“We’re interested in finding out how we can change the way light behaves, and how that could be useful,” Eastham explained in a statement. “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.”
Findings could result in new forms of quantization
Donegan, whose research focused on the field of light’s behavior at the nanometer scale (better known as nanophotonics), explained that a beam of light is characterized by its color, wavelength and angular momentum, which measures the degree to which something is rotating.
“For a beam of light, although travelling in a straight line it can also be rotating around its own axis. So when light from the mirror hits your eye in the morning, every photon twists your eye a little, one way or another,” he said. “Our discovery will have real impacts for the study of light waves in areas such as secure optical communications.”
The Trinity College-led team made their discovery using a 200-year-old technique which found that when a ray of light passed through certain crystals, it would become a hollow cylinder that could be used to generate beams with a screw-like structure. By analyzing the light beams using the theory of quantum mechanics, the researchers were able to predict that the these particles (or photons) would have a half-integer total angular momentum.
To test out that prediction, they came up with an experiment in which they used a specially made device to measure the flow of angular momentum in a beam of light. This also enabled them, for the first time, to measure the variations in this flow created by quantum effects, the study authors said in a statement. Their experiments revealed that a tiny shift, just one-half the size of Planck’s constant, in the angular momentum of each photon.
“We conclude that for light, as is known for electrons, reduced dimensionality allows new forms of quantization,” the authors wrote. Their findings confirm something that theoretical physicists have long suspected: that particles which are free to move in only two dimensions could result in unusual new possibilities, including the existence of particles with quantum numbers that are just a fraction of those that had been expected.
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