Exceptional Points Could Stop Light Waves in their Tracks?

January 6, 2018

Light moves fast, which is kind of the whole point of light, or at least that’s what most people think of it. That’s kind of the whole point of light, or at least that’s what most people think of it. Light shoots through the 93 million miles between Earth and the sun in just eight minutes, it spreads its message around the world almost instantly, and its top speed of 186,000 miles per second (300,000 kilometers per second) turns out to be the absolute speed limit for the entire universe.

But there are some physicists who are interested in subverting this property of light and reducing its speed considerably. And in a new paper published on January 3 in the journal Physical Review Express and arXiv, a team of researchers has shown that it is possible to make light stop absolutely at certain “special points.”

This isn’t the first technique scientists have come up with to slow down the speed of light. Back in 2001, a paper published in the journal Nature (and explained in the New York Times) showed that light could be imprinted on supercooled atoms in such a way that it would stop altogether – and then be jogged by a second pulse of light that would keep it on its merry way.

But the technique described in this Jan. 3 paper doesn’t rely on supercooled atoms or imprinted light. Instead, it relies on some interesting quirks about how waves – including light waves – behave in the unusual case of “special points.”

But in fact, real-world waves – whether they are composed of light, sound, or quantum vibrations – are richer, more complex three-dimensional shapes that constantly change according to the properties of the container they are moving through.

By making just the right adjustments to the properties of the container, scientists have figured out how to fold a complex wave into its mirror twin. The phenomenon occurs at particular points, or points where the wave exhibits unusually strange behavior. Shoot a beam of light and its mirror twin into that point from one direction, and both will look the same as the original beam. Emit it from the other direction, and both will appear to look like mirror waves.

In this paper, the scientists show that it is theoretically possible to adjust the properties of the special point and the beam so that the light stops moving completely at that special point. Change the properties and the beam again, and the light will continue to move happily.

For a long time, scientists thought that the special point was a purely theoretical concept. But back in 2010, researchers were able to build one in the real world that emits microwaves through a special metal box that flips the wave pattern from one mode to another.

Researchers have yet to build a photo-stop special point in the real world – whether anyone will do so remains to be seen. In a statement from the team behind the photo-stop special point paper, the researchers said their next step is to figure out if a similar special point could block other kinds of waves, such as sound.

Going forward, the team wrote in the paper, they expect the rise in research on special points to help solve important problems in quantum mechanics and point the way to new techniques that rely on bending and shaping waves.