"One of the challenges in such an experiment, which was carried out entirely on one chip, was the proximity of the excitation laser to the detectors on the chip," explain Ekkehart Schmidt from KIT and Mario Schwartz from the University of Stuttgart. "The detectors cannot distinguish which photons come from the laser and which from the quantum dot. This leads to unwanted detections." Schmidt and Schwartz have significantly reduced the influence of the laser photons by placing reflective metal layers on the chip.
Nanometer-sized structures - so-called quantum dots - on a platform made of gallium arsenide serve as efficient sources of single photons. Optical logic circuits and special detectors made of superconducting nanowires can also be placed on the same chip. In the experiment carried out by the Knowledgexhaftists, single photons emitted by an optically pumped quantum dot were guided in a photonic waveguide and divided by a beam splitter into two waveguide arms, each equipped with a detector.