This outcome essentially reveals a new form of light.
Quantum computing relies on freaky 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. But vaporizing rubidium with a laser and keeping it ultracold creates a cloud the researchers contain in a small tube and magnetize. Then scientists used lasers to send photons into the cloud, which slowed down and exited the cloud as pairs or triplets.
The full statement from MIT follows below. Photons from two beams of normal light from flashlights, on the other hand, would pass right through each other. Notice anything peculiar? The rather anticlimactic answer is, probably not. The basic reason why is because the photons that make up light do not interact with one another.
This suggested 'some kind of interaction - in this case, attraction - taking place among them, ' MIT said. But before would-be Jedis start demanding their sabers, the advance is far more likely to lead to intriguing new ways of communicating and computing, researchers report this week in Science. This could be a potential step toward quantum computation. They never appeared to interact with each other, explaining why beams of light intersect and do not reflect with each other.
Normal photons also do not have mass and travel at a speed of 300,000 kilometers per second, but the researchers found that the bound photons acquired some mass, equivalent to a fraction of that of an electron's.
The new form of light happens when three photons stick together, which is remarkable given that the light particles typically refuse to interact.
Vuletic says the results demonstrate that photons can indeed attract, or entangle each other.
Although the entire interaction within the atom cloud took place in just over a millionth of a second, the photons remained bound together, even after they traveled out of the cloud. "It's very uncharted territory".
A team of researchers from MIT and Harvard were able to make photons interact by sending them through an ultracold, dense cloud of rubidium atoms.
The team observed that when three-photon groups exited the atom cloud, the photon phase was shifted, compared to when the photons did not interact, and was three times larger than the phase shift of two-photon molecules.
It isn't the first time the researchers have observed this kind of interaction, however.
"For example, you can combine oxygen molecules to form O2 and O3 (ozone), but not O4, and for some molecules you can't form even a three-particle molecule", Vuletic says.
To find out, the team used the same experimental approach they used to observe two-photon interactions.
The cloud of rubidium atoms was cooled to just one millionth of a degree above absolute zero, slowing the atoms to a near standstill. This keeps the rubidium atoms diffuse, slow moving and in a highly excited state. The same process could occur with another photon traveling simultaneously through the cloud.
When photons and atoms bind, they create "polaritons".
The photons exited the cloud bound together in pairs or triplets. A photon's phase indicates its frequency of oscillation. "The more you add, the more strongly they are bound", says Venkatramani.
This slowed the atoms down until they were almost still, sending only a few photons through the cloud at one time.
When a photon lands on an atom, they can form a hybrid photon-atom or polariton. The physicists measure the photons when they exit the other side of the cloud and that is when things get weird.
The scientists discovered that this phenomenon can also occur with three photons.
"What was interesting was that these triplets formed at all", said Vladan Vuletic, a co-lead author of the study and the Lester Wolfe Professor of Physics at MIT.
"These pairs and triplets also give off a different energy signature, a phase shift, that tells the researchers the photons are interacting", cited by Smithsonian magazine.