Physicists Create New Type of Light

A group of German researchers from the University of Bonn say that they were able to develop a new state of matter, which contains a new type of photons, the elementary particles that make up light.

The stuff was obtained when the team, led by researchers Jan Klärs, Julian Schmitt, Frank Vewinger and Martin Weitz, managed to cool photons until the particles entered a blob-like state.

This particular state can be added right next to solids, liquids, gases and plasma, as it represents a newly found state of matter, called a Bose-Einstein condensate.

This is not the first time that such a condensate is obtained. The first time was in 1995, but the team that created it used super-cold atoms of a gas. The new study marked the first time photons were used to obtained a BEC.

The German team decided to call the new particles “super-photons,” because they tend to merge with one another when they are cooled down to nearly absolute zero. As this happens, they form a blob in which individual particles are no longer distinguishable.

This means that the entire BEC acts like one giant particle, a super-photon for all intents and purposes.

In theoretical studies preceding these experiments, physicists hypothesized that it would not be possible to use photons for creating this state of matter, on account of the fact that these particles have no mass.

Usually, when they are cooled down to such low temperatures, they tend to get absorbed by their surroundings and disappear, which literally leaves researchers empty-handed, LiveScience reports.

“Many scientists believed that it would not be possible, but I was pretty sure that it would work,” Weitz says, adding that the main challenge was dropping the overall temperature of the photons without significantly reducing their numbers.

In the experimental setup the researchers devised, very small mirrors were placed about 1 micron apart in a very specific configuration, which allowed them to trap the photons without them being absorbed.

Tiny droplets of color pigments were then placed in this system. This was done to allow for the photons to be absorbed, and then re-emitted, essentially preserving their numbers.

The constant bouncing eventually cooled down the photons to room temperature, which was enough for them to start coalescing into a condensate. Details of the experiment appear in the November 25 issue of the esteemed journal Nature.

“Whether a temperature is cold enough to start the condensation depends on the density of the particles. Ultra-cold atomic gases are very dilute and they therefore have very low condensation temperatures,” said Klärs in an e-mail.

“Our photon gas has a billion times higher density and we can achieve the condensation already at room temperature,” the expert concluded.