Distilling perfect photons for a better quantum computer

Researchers from the University of Twente have improved the quality of photons to such an extent that building quantum computers based on light becomes cheaper and more practical. “For a photonic quantum computer, you need extremely high-quality photons. Our technique ensures that only the best photons remain, which is crucial for reliable calculations,” comments lead researcher Jelmer Renema.

Because quantum computers are extremely sensitive to errors, previous methods required hundreds of physical photons to make a single reliable photonic qubit. The new method can replace part of the necessary error correction, requiring far fewer photons.

Whereas previous methods focused on error correction afterwards, the UT researchers tackled the problem at the source. They designed a component that can distil a single high-quality photon from a brew of imperfect ones. To do this, they devised an optical circuit consisting of programmable light guides and detectors. By exploiting the quantum properties of light, they created a Schrödinger’s cat-like state in which photons are more likely to assume ‘good’ rather than ‘bad’ properties. As in Schrödinger’s famous thought experiment, measurement ultimately determines whether a photon has retained the desired properties.