Physicists Form New Matter By Coaxing Photons Into Molecules

By Wesley Fenlon

Physicists compare photonic molecules to lightsabers, which is exciting, but they may prove important for quantum computing, which is almost as cool.

Science has done it. The seemingly impossible. Discovering the secret to what was, until now, certainly fictional. The lightsaber.

"Harvard Professor of Physics Mikhail Lukin and MIT Professor of Physics Vladan Vuletic have managed to coax photons into binding together to form molecules – a state of matter that, until recently, had been purely theoretical," writes Phys.org. "Photons have long been described as massless particles which don't interact with each other. 'Photonic molecules,' however, behave less like traditional lasers and more like something you might find in science fiction – the light saber."

Photo via Ro-Lightsaber.Blogspot.com

Okay, so they haven't actually invented a lightsaber. Unfortunately. The photonic molecules aren't naturally taking the form of a sword that can cut through anything in existence. But the principle is similar, say the physicists. Normally photon have no mass and don't interact with one another. The experiment created a medium that caused photons to bind into molecules. Lukin said "When these photons interact with each other, they're pushing against and deflect each other. The physics of what's happening in these molecules is similar to what we see in the movies."

Speaking practically, though, this discovery is more likely to benefit quantum computing than sci-fi sword fights. Photons are the best form to carry quantum information, but until now, they haven't been able to interact. There's now a proof-of-concept for how photons could help push quantum computing forward.

Explaining how the photons form molecules is a little complicated. The key is an effect called the Rydberg blockade, which came into effect when the physicists put rubidium atoms in a vacuum chamber and chilled them to near-absolute zero. When they fired individual photos into the atom cloud using lasers, the photons excited atoms along their path, passing energy off as they went. And then, the Rydberg blockade. PHys.org explains:

"When an atom is excited, nearby atoms cannot be excited to the same degree. In practice, the effect means that as two photons enter the atomic cloud, the first excites an atom, but must move forward before the second photon can excite nearby atoms.

The result...is that the two photons push and pull each other through the cloud as their energy is handed off from one atom to the next."

Now: How do we get that in the form of a sword?