Scientists Create New Form of Matter: Photon Molecules Act Like a Light Saber

Want to channel the Force and wield a light saber? You may not be able to do the former, but scientists have now taken a step closer to creating the tools traditionally used by Jedi in the Star Wars films. Researchers have managed to coax photons into binding together to form molecules, a state of matter that, until recently, had been purely theoretical.

The nature of light has undergone decades of research. Photons, which are particles of light, have long been described as massless particles which don't interact with each other. For example, if you shine two laser beams at each other, they simply pass through one another. Yet these newly dubbed "photonic molecules" behave less like traditional lasers but are more like, well, a light saber.

"Most of the properties of light we know about originate from the fact that photons are massless, and that they do not interact with each other," said Mikhail Lukin, one of the researchers, in a news release. "What we have done is create a special type of medium in which photons interact with each other so strongly that they begin to act as though they have mass, and they bind together to form molecules."  

Lukin continued, "It's not an in-apt analogy to compare this to light sabers. When these photons interact with each other, they're pushing against and deflect each other. The physics of what's happening in these molecules is similar to what we see in the movies." 

In order to get the photons to bind to each other, the researchers pumped rubidium atoms into a vacuum chamber. They then used lasers to cool the cloud of atoms to just a few degrees above absolute zero. Then, using extremely weak laser pulses, they fired single photons into the cloud of atoms.

When the photons entered the cloud of atoms, the energy excited atoms along the path of the photons. This caused individual photons to slow dramatically. As the photon moved through the cloud, the energy is handed off from atom to atom and eventually exited the cloud with the photon. What was more interesting, though, was that the photons bound together and would exit the cloud as a single molecule.

"It's a photonic interaction that's mediated by the atomic interaction," said Lukin in a news release. "That makes these two photons behave like a molecule, and when they exit the medium they're much more likely to do so together than as single photons. We do this for fun, and because we're pushing the frontiers of science, but it feeds into the bigger picture of what we're doing because photons remain the best possible means to carry quantum information."

In fact, the new research has practical uses for potentially building quantum computers. That said, it will be quite some time before anything like a light saber will come out of the laboratory. Even so, it's a huge leap forward for the study of light, and scientists are hopeful for future applications.

The findings are published in the journal Nature.