As most already know, light is made up of massless particles called photons. Photons are tricky little buggers, as when they can act as a particle and a wave at the same time, and travel incredibly fast... The speed of light, in fact. Scientists have long believed that photons don't interact with one another, because again, they have no mass. You can even cross two incredibly powerful lasers, and you won't see an interference in either. Researchers, however, have found a way to make photons bond together into "molecules" that act as if they do have mass! It's all possible with lasers and incredibly cold gas. Ready to read about some Super Cool Science S#!t?
though it would be another 6 years before the theory was proven. In 2013, researchers at the MIT-Harvard Center for Ultracold Atoms pumped supercooled rubidium gas into a vacuum chamber. Using incredibly weak lasers, they started by firing single photons into the cloud. As the photons travel through the cloud, they excite atoms along their path, exchanging energy between mediums, and significantly slowing the photon. After exiting the cloud, the single photon is still a single photon, unchanged from when it entered.
When they fired two photons through the cloud,they were very surprised to learn that they had "paired up", exiting the cloud as a single "molecule" made completely of light! They discovered that these photons weren't simply clumped together, but were instead bonded, like normal matter would. What causes this phenomenon is the way photons interact with atoms on the quantum level.
When atoms in the laser's path become excited by one of the photons, other atoms in the immediate vicinity cannot be excited to the same degree. The next photon is unable to pass off energy, and the group forms an atom/photon hybrid called a polariton. The first photon must move forward in order for the second to excite an atom, creating a sort of tug-o-war that pushes and pulls each photon along with the other, passing off energy around as they go. Their constant back and forth interactions with the atoms around them force them to interact with each other, and when they exit the other side of the cloud, they remain entangled.
A few months ago, the same team did it again, and this time, they created molecules of light with three photons! They used the same method they had a few years back, and now are wondering whether they can create even larger photonic molecules. This could blow the lid open for quantum computing, as one of the largest hurtles has been making light interact with other light... Light is one of the most efficient method of carrying quantum information, and being able to form particles from it that act as if they mass could create whole new avenues of computing, on scales we've never imagined.
