Science & Technology

Physicists Have Created a New Form of Light

Particles tend to interact. The interacting particles you're probably most familiar with are electrons, the negatively charged hangers-on of an atom. But not all particles interact: photons, which are particles of light, are introverts. These massless particles wander the universe never canoodling with another particle. That's too bad for us: if they could interact, it might make all sorts of technology possible, from quantum computers to lightsabers. Good thing an MIT and Harvard research team has figured out a way to do it, eh?

What Happens in the Cloud Stays in the Cloud

In two different studies, one published in the journal Nature in 2013 and another another published in the journal Science in 2018, a team led by MIT physics professor Vladan Vuletic and Harvard physics professor Mikhail Lukin figured out a way to make photons interact by using a cloud of rubidium atoms. They cooled that cloud to a temperature just a millionth of a degree above absolute zero, making the atoms densely packed and nearly motionless. Then they shot it with a weak laser beam that sent just a few photons through at a time and measured what came out the other side.

What they found was pretty exciting. Normally, the photons would exit the cloud at random intervals as solo travelers, just like they always have. But the team found that even though they entered the cloud as individuals, these photons exited in pairs — and even triplets. Not only that, but a particular energy measurement known as "phase" was even greater. The triplets had a phase shift three times larger than the pairs. "The phase tells you how strongly they're interacting, and the larger the phase, the stronger they are bound together," co-author Aditya V. Venkatramani explained in a press release.

The researchers aren't sure what went on in the cloud, but they've formed a hypothesis. As one photon moves through the atomic cloud, it hops from atom to atom until it reaches the other side. If two photons land on the same atom, they form what's known as a polariton — a sort of photon-atom hybrid. That atom is what lets the two (or three!) photons interact and bind together. Then, they leave their atom where it is and exit the cloud, albeit 100,000 times more slowly than the speed at which they came in thanks to their newfound mass.

Light Me Up

What's so special about interacting photons? Well, photons are the leading candidate for creating quantum computers, which are currently in their infancy but can work millions of times faster than conventional computers. One key to this lightning speed is the quantum phenomenon of entanglement: correlations between two particles that can increase the power of a computer exponentially. When photons interact, they can create these correlations. "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," Vuleti says.

The team didn't comment on the possibility of lightsabers, but we're hoping. After all, you can't create swords out of light if that light refuses to interact with anything. If you could control these little clusters of interacting photons, you might be able to create weapons that actually do some damage — or at least bounce off of each other for fun.

Quantum physics is complicated, which is why Terry Rudolph wrote "Q is for Quantum" as a straightforward guide to the quantum world. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will receive a share of the sale.

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Written by Ashley Hamer March 27, 2018

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