They were also traveling about 100,000 times slower than typical photons.
Researchers observed groups of three photons not only interacting, but effectively combining to form a completely new type of photonic matter. Photons from two beams of normal light from flashlights, on the other hand, would pass right through each other. Typically, photons don't interact with each other, which is why you don't see light beam bounce off each other - that would be a weird sight.
Researchers measured the photons as they exited through to the other side of the atom cloud. Rather than emerging from this cloud separately, the photons within the laser merged bound in groups of three. The results suggest some kind of interaction taking place among the light particles.
It isn't the first time the researchers have observed this kind of interaction, however. "The more you add, the more strongly they are bound", says Venkatramani. "It was also not known whether they would be equally, less, or more strongly bound compared with photon pairs".
In order to get the photons to interact, the scientists shone a weak laser beam through an ultracold atom device (pictured).
'So it was an open question: Can you add more photons to a molecule to make bigger and bigger things?' They proposed that, as a single photon moved through the atom cloud, it briefly landed on a nearby atom, then moved on to another atom until it reached the other end of the cloud. "With repulsion of photons, can they be such that they form a regular pattern, like a crystal of light?" But can they can be forced to interact or bind together? Some photons would repeal each other, pushing apart until they find their own space, while others hold the larger formation and keep the repealing ones from scattering.
These polaritons would interact in the cloud and exit the cloud still bound together. Photon correlation and conditional phase measurements revealed the distinct bunching and phase features associated with three-photon and two-photon bound states. The physicists' theoretical model suggests that as a single photon moves through the cloud of rubidium, it hops from one atom to another, "like a bee flitting between flowers", the press release explains.
If two polaritons are moving through a cloud, they can interact and exit the cloud still bound together. Then scientists used lasers to send photons into the cloud, which slowed down and exited the cloud as pairs or triplets. Einstein's least-favorite physics phenomenon (he called it "spooky action at a distance"), quantum entanglement occurs when two particles become linked, so that when one changes, the other does, too.
Cantu, his colleague Aditya Venkatramani, a Ph.D. candidate in atomic physics at Harvard University, and their collaborators start by creating a cloud of chilled rubidium atoms.
"What's neat about this is, when photons go through the medium, anything that happens in the medium, they "remember" when they get out", Cantu says.
Typically, in a vacuum, photons travel at the speed of light (almost 300,000 kilometers/second) and have no mass.
This means that photons that have interacted with each other, in this case through an attraction between them, can be thought of as strongly correlated, or entangled - a key property for any quantum computing bit.
Now that photons have been shown to interact, they could be used in a variety of new applications.
Quantum computing relies on freakish mechanics like hyper-cooled atoms and quantum superposition to pull off seemingly impossible calculations, but now scientists have made an even weirder breakthrough: they've created a new form of light, which may prove essential for the quantum computer revolution. This could be a potential step toward quantum computation.