Single photons can be reliably detected for data transmission and quantum computing by integrating detectors with nanophotonic chips, an international team has discovered. Ultrafast, efficient and reliable single-photon detectors suitable for practical application are among the most sought-after components in photonics and quantum communication. Dr. Wolfram Pernice, a physicist at Karlsruhe Institute of Technology (KIT), working with colleagues at Moscow State Pedagogical, Yale and Boston universities, fabricated superconducting nanowires directly on top of a nanophotonic waveguide. The resulting single-photon detector combines near-unit detection efficiency with high timing resolution, and it has a very low error rate. The single-photon detector is characterized by five convincing factors: 91% detection efficiency; direct integration on chip; counting rates on a gigahertz scale; high timing resolution; and negligible dark counting rates. A prototype developed at Yale in collaboration with KIT achieved a detection efficiency of 91 percent when tested in the telecommunications wavelength range. This was carried out as part of the Integrated Quantum Photonics project at the German Research Association’s Center of Functional Nanostructures. The detector’s on-chip installation allows it to be replicated at random. Single-photon detectors built to date were stand-alone units connected to chips with optical fibers, a design that leads to photons being lost in the fiber connection or being absorbed. Such losses are eliminated when the detector is fully embedded in a silicon photonic circuit. Superconducting single-photon detector. On the left: Light-microscopy image of the component with optical input circuit, electrical contacts and superconducting single-photon detector. Erroneous photon detection – known as dark count – is reduced with the new design, which also provides ultrashort timing jitter of 18 ps. Although the prototype was designed to work in the telecom wavelength, the same architecture can be used for those in the visible spectrum, the researchers say, something that would allow the device to be used in the analysis of structures that emit very little light, such as single molecules or bacteria. The results were published in Nature Communications (doi: 10.1038/ncomms2307).