Physicists Have Made the Second-Ever Observation of Interacting Photons

Strange Photons

Those of us who grew up watching Luke and Leia on screen have probably wondered at one point or another why we don't have lightsabers. The basic reason why is because the photons that make up light do not interact with one another. Yet according to a new study published in the journal Science, interacting photons can be created in the lab. Beyond sci-fi-inspired applications, this new development could also play a huge role in actualizing quantum computers.

Researchers observed groups of three photons not only interacting, but effectively combining to form a completely new type of photonic matter. This outcome essentially reveals a new form of light.

To make interacting photons, the team shone a weak laser through a cloud of cold rubidium atoms. Rather than emerging from this cloud separately, the photons within the laser merged bound in groups of three. This observation suggests a form of interaction and attraction — also known as entanglement — between photons.

Among the observations that the researchers made, they also noticed that the normally zero-mass photons had taken on a fraction of an electron's mass when bound together. They were also traveling about 100,000 times slower than typical photons.

Next Stop: Quantum Computing

This work builds off the first-ever observation of interacting photons, which this team documented in 2013. According to MIT physics professor Vladan Vuletic in a press release: "The interaction of individual photons has been a very long dream for decades." 

The team believes that photon interactions could be manipulated in ways that make them an asset to quantum computing. Entangled photons could be used to distribute information in a quantum system. Quantum computing carries information using bits that represent both a binary 0 and 1 simultaneously, which may be facilitated by closely entangled photons.

"Photons can travel very fast over long distances, and people have been using light to transmit information, such as in optical fibers," Vuletic said in the press release. "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."