Ordinarily, crossing light streams (such as shining two flashlights so that they converge) does nothing out of the ordinary. This is because the individual light particles, aka photons, do not interact with one another. However, physicists at the Massachusetts Institute of Technology and Harvard University have found a way to change that by forcing groups of up to three photons to bound together in a way that forms a completely new kind of photonic matter.
“In a vacuum or in regular materials, photons do not interact with each other, and mostly just pass through one another,” Vladan Vuletic, the Lester Wolfe Professor of Physics at MIT, told Digital Trends. “Using a laser-cooled atomic gas we have created a medium where one photon interacts very strongly with another — so strongly that they can, in fact, bind together, and travel together at a speed 100,000 times smaller than the regular speed of light in vacuum. We have found that not only can two photons bind together, but also three. This is analogous to two oxygen molecules forming molecular diatomic oxygen (O2), but also ozone (O3). This can be thought of as forming tiny droplets of light.”
Inventing a whole new type of light is pretty cool in its own right, but it may have practical application, too: Potentially in quantum computing.
“Light is very good for transporting information over long distances through fibers, but without interactions, light can only transport information, not do anything more interesting like computing,” Vuletic continued. “So a prerequisite for quantum computing using light is to induce interactions between photons, which we have done.”
A more easily realizable short-term goal than quantum computing is to make “optical transistors,” transistors where light directly switches light. These transistors could be potentially faster than a conventional transistor and may dissipate less power. However, Vuletic notes that this is still early days and that even this feat is technologically challenging.
“So far, we have only made attractive interactions between photons, but in many respects, repulsive interactions, where photons bounce off each other like little hard balls, are more interesting,” he said. “We have made first progress in this direction. Then we will try to make a single-photon optical transistor where one photon switches on or off a stronger light beam.”
A paper describing the work was recently published in the journal Science.