Rigid light is a strange new state of matter oxygen/Getty

There’s a new state of matter — and it’s weird. It’s made from light and is somewhere between a solid and a superfluid. It can’t be stirred, rotated, or even pushed.

“If you have some water in a pipe and you start pushing it, it will flow a little faster,” says Marzena Szymańska at University College London. “Whereas this fluid is so rigid that even pushing it will not change its velocity.”

The new state is made from “liquid light”. This is a fluid consisting of light trapped in another material, where each photon is coupled with another particle. These particles, called polaritons, can flow and interact with one another in a way that photons alone cannot.


In the last decade or so, experiments have shown that liquid light can become a superfluid — a fluid which flows with no viscosity or friction. Because of the lack of friction, superfluids cannot be stirred or rotated. If you put a superfluid in a bucket and rotate the bucket, the fluid itself will remain stationary.

Read more: Physics adventures down the superfluid supersonic black hole

But Marzena Szymańska and her colleagues calculated that, in certain situations, a fluid made of polaritons takes things one step further: not only can it not be rotated, its flow cannot be changed at all. They call this new phase of matter and light a rigid state.

That’s because of how a polariton fluid is created. Some photons are always leaking out of the trap, so researchers constantly replace them using a laser. The team found that the laser sets the properties of the fluid from the outside, so they cannot be changed.

It’s not yet clear what this strange rigid light could be used for, but could one day find a use in optical communications, says David Snoke at the University of Pittsburgh in Pennsylvania. “Even if it’s not good for anything, it’s interesting because it’s different,” says Snoke. “It really is a new phase of matter.”

Journal reference: Nature communications, DOI: 10.1038/s41467-018-06436-2