Generally speaking, light particles don’t want anything to do with one another. In fact, they can pass through each other without any effect whatsoever. Despite that, a team of researchers at the Vienna University of Technology may have opened new doors for quantum technology applications by using thin pieces of glass to get two photons to interact.

Scientists were previously able to affect photons using “non-linear media,” but only at high light intensities, meaning countless photons were present. The newest research allows scientists to manipulate interaction between just two photons, which theoretically makes possible all manner of quantum optics applications.

Some unusual hardware is necessary to the interaction. The researchers created a micro-thin glass fiber, which is then attached to a tiny bottle-shaped device called a resonator. Sending a photon through the resonator actually inverts it phase 180 degrees.

When two photons are sent to the resonator at the precise same time, they both experience the joint phase shift. As such, two photons interacting behave in different ways than individual photons.

“It is like a pendulum, which should actually swing to the left, but due to coupling with a second pendulum, it is swinging to the right. There cannot be a more extreme change in the pendulum’s oscillation”, says Professor Arno Rauschenbeutel. “We achieve the strongest possible interaction with the smallest possible intensity of light.”

Photon interaction is essential to just about every quantum optic technology, including quantum teleportation and quantum computing. The good news is that the hardware is somewhat low-tech: Glass fiber optics are already used en mass today, and the glass resonators are perfectly compatible with current systems. The creation of a strong deterministic photon-photon-interaction is an important step towards a global quantum information network for the tap-proof transmission of data.