Stopping Light Cold: Australian Scientists Freeze Photons for Use in Quantum Computers

 Researchers from The Australian National University (ANU) have developed a method of freezing and storing light, an important step on the road to developing quantum computers. Most switches used in quantum computing experiments are made up of trapped ions or semiconductor particles, suspended in a state of quantum superposition. Photons, however, could interface much more efficiently with fiber optic networks, without the need for a way to translate the information between the qubit — the quantum-computing equivalent of a classical computer bit — and the computer’s network or interface.

The problem is that photons, moving at the speed of light, don’t stand still long enough for them to be used as computer switches. This new AMU experiment made use of a light trap by firing an infrared laser into an atomic vapor of rubidium-87, chilled to near-absolute zero. While the vapor absorbed some of the laser’s energy, a portion of the photons remained suspended amongst the cold atoms.

"It’s clear that the light is trapped, there are photons circulating around the atoms," says lead researcher Jesse Everett. "The atoms absorbed some of the trapped light, but a substantial proportion of the photons were frozen inside the atomic cloud."

"Corralling a crowd of photons in a cloud of ultra-cold atoms creates more opportunities for them to interact," explains Dr. Geoff Campbell from RSPE and ARC Centre of Excellence for Quantum Computation and Communication Technology at ANU.

Unlike the interactions that can be facilitated between ordinary atoms, photons typically simply whiz by one-another, without interacting, meaning there’s no exchange of information between them. Freezing them in the new process, however, opens up the possibility of enabling them to interact.

"We’re working towards a single photon changing the phase of a second photon. We could use that process to make a quantum logic gate, the building block of a quantum computer," continues Dr. Campbell.