Working in close collaboration, researchers from Paderborn University, the University of Basel and Ruhr University Bochum have made a breakthrough in quantum communication. In their recently published paper in the journal Physical Review Letters, they demonstrate how special semiconductor nanostructures can be used to generate individual photons and pairs of photons that are almost perfectly identical. These “indistinguishable” particles form the basis for quantum entanglement and quantum interference.

In quantum information processing, photons are ideal carriers of information. However, to use these light particles for complex calculations, they must possess exactly the same properties—an aspect known as “indistinguishability.” Until now, such sources have suffered from the fact that the photons generated were temporally correlated or out of focus, which greatly reduced their indistinguishability and thus their quality.

A team of doctoral candidates from Basel and Paderborn has now solved this problem using a process known as “biexciton decay” in semiconductor quantum dots within an optical resonator. This is a process in which a molecule consisting of two bound excitons (each a pair comprising an electron and an electron hole) decays, leaving behind a single exciton and a photon.