The fact that the speed of light in a vacuum is a constant is one of the cornerstones of physics, but scientists from the Philippines were able to add a twist to this tenet. And I mean it literally!
By changing how some light beams rotate, the researchers from the National Institute of Physics were able to slow down light in a vacuum. The physicists used circularly symmetric light beams, known as Laguerre-Gauss beams, to change the way light twists around itself. Suddenly, the light beams were propagating more slowly.
The speed of light varies when it moves through different materials, and it does so at the expense of accuracy in transmitting information. For this reason, more and more people are interested in ways of manipulating the speed of light without affecting accuracy.
Last year, researchers from the University of Glasgow were able to slow down light using a "mask," turning plane waves (where the wavefronts are parallel to each other) into conical waves. In this latest research, published in Scientific Reports, the physicists also focused on non-plane waves, but they don’t change their shape.
The waves they looked at have an "orbital angular momentum," which could be visualized as a light beam following a tight corkscrew path. Each Laguerre-Gauss light beam carries its own angular momentum and the researchers were able to slow them down without directly interfering with them.
The fantastic result doesn’t violate any law of physics; individual photons are not suddenly moving more slowly, they are simply sent on a longer path, so the light beam arrives later. The physicists were even able to calculate exactly how much later they would arrive at the target before they did the experiment.
While the research seems very abstract, it has wide applications in computing technologies and telecommunications, where Laguerre-Gauss beams are commonly used. This might not be faster-than-light data transmission, but it might just help us in getting even better at sending information around the globe.