Vaporizing rubidium with a laser and keeping it ultracold creates a cloud the researchers contain in a small tube and magnetize. This keeps the rubidium atoms diffuse, slow moving and in a highly excited state. A weak laser is than fired at the cloud. The physicists measure the photons when they exit the other side of the cloud. After passing through the cloud, the photons creep along 100,000 times slower than normal. The photons come through in pairs or triplets which give off a different energy signature because the photons are interacting. Surprisingly, the researchers discovered that the three-photon grouping is even more stable than two.
How three individual photons look
The physicists’ theoretical model suggests that as a single photon moves through the cloud of rubidium, it hops from one atom to another, “like a bee flitting between flowers.” Playing with the interaction could reveal new insights into how energy works or where it comes from. Photons bound together in this way can carry information—a quality that is useful for quantum computing. The researchers want control the attractive and repulsive interactions of photons so precisely that they could arrange photons in predictable structures that hold together like crystals, which will be good for quantum communication.