Physicists Have Made the Second-Ever Observation of Interacting Photons

Physicists Have Made the Second-Ever Observation of Interacting Photons

Physicists Have Made the Second-Ever Observation of Interacting Photons

Currently, researchers posit that this special form of light could be useful for quantum computing and the creation of uncrackable codes, ultra-precise clocks, unimaginably powerful computers and more.

The new form of light happens when three photons stick together, which is remarkable given that the light particles typically refuse to interact.

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. But can they can be forced to interact or bind together?

The photon dance happens in a lab at MIT where the physicists run table-top experiments with lasers. Rubidium is an alkali metal so it typically looks like a silver-white solid.

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The scientists evaporated rubidium with a laser, but kept the resulting cloud in an ultracold state. Cooling the atoms slows them to a near standstill.

The researchers then measure the photons as they come out the other side of the atom cloud.

Normally the photons would be traveling at the speed of light-or nearly 300,000 kilometers per second. "But after passing through the cloud, the photons creep along 100,000 times slower than normal", Smithsonian reported. In particular, photon correlation and conditional phase measurements reveal the distinct features associated with three-photon and two-photon bound states. In 2013, the effort paid off, as the team observed pairs of photons interacting and binding together for the first time, creating an entirely new state of matter.

"Initially, it was unclear", says Venkatramani. However, it turned out that groups of three photons were more stable than double groups. The observed bunching and strongly nonlinear optical phase are quantitatively described by an effective field theory (EFT) of Rydberg-induced photon-photon interactions, which demonstrates the presence of a substantial effective three-body force between the photons.

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Surprisingly, the researchers discovered that the three-photon grouping is even more stable than two. "The more you add, the more strongly they are bound", Venkatramani noted.

But how do the photons get together? Their model, based on physical principles, puts forth the following scenario: As a single photon moves through the cloud of rubidium atoms, it briefly lands on a nearby atom before skipping to another atom, like a bee flitting between flowers, until it reaches the other end. And it is this interaction that triggers photons to remain bound together, even after they've left the cloud. Instead, they simply pass each other by, like indifferent spirits in the night. "If photons can influence one another, then if you can entangle these photons, and we've done that, you can use them to distribute quantum information in an interesting and useful way". The thing that is so attractive about encoding information in photons is that photons can carry their information across distances very quickly.

The team also found that the ordinarily weightless photons gained mass, albeit a fraction of an electron's mass, said a Daily Mail report, which termed the double-photon bond as a "new form of light". 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.

In their more farout fantasies, researchers envision arranging photons into organized structures not unlike crystals, which are thought to be useful in quantum communication.

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The results prove for the first time that photons of light can indeed attract - or entangle - one another.

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