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Let There Be One Molecule of Light

A Harvard research team has managed to bond photons into a single unit of light. While it's not a lightsaber yet, it's a start.

by Ben Richmond
Sep 26 2013, 4:00pm
A seperate US Air Force laser study, via Wikimedia Commons

Every claim of Star Wars becoming reality warrants my full attention, so when Harvard and MIT researchers say, “It's not an in-apt analogy to compare this to lightsabers,” I’m there. Turns out they didn’t build something awesome like a sword made of light; instead, they essentially created a new form of matter out of photons.

Unlike atoms, which are always bonding together to form things like the air or people, photons were thought to be massless, and known to just pass right by each other. You can cross two laser beams without disrupting either one. But now a research team, lead by Harvard Physics Professor Mikhail Lukin, has managed to get photons to get together. 

“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 said in a press release. “This type of photonic bound state has been discussed theoretically for quite a while, but until now it hadn't been observed.”

In order to bind the photons, the researchers pumped rubidium atoms into a vacuum tube and chilled them down almost to absolute zero, and fired weak laser pulses to send photons into the cloud of cold atoms. While passing through the gas, the photons slowed down. When two photons were fired at the same time, they exited together, like a molecule.

Photons with strong mutual attraction in a quantum nonlinear medium, via Nature

The results, published in Nature, aren’t the first attempt by physicists to create what they call a “molecule of light,” which has a potential practical application in the field of quantum computing.

"We do this for fun, and because we're pushing the frontiers of science," Lukin said. "But it feeds into the bigger picture of what we're doing because photons remain the best possible means to carry quantum information. The handicap, though, has been that photons don't interact with each other.”

So it’s a little bit less immediately badass as a laser sword fight, but still, new forms of matter are pretty impressive. There’s a possibility of someday forming crystals of light, which is also pretty stellar. And anyway, as the prequels taught us, there’s more to life than lightsabers.