The superconducting nanowire detector, first developed in 2001 at the Moscow State Pedagogical University, is a device exploiting the phenomenon of superconductivity to achieve high-speed photon detection. These superconducting single photon detectors (SNSPDs) provide single-photon sensitivity from optical to mid-infrared wavelengths, low dark count, short recovery time and low timing jitter.
The NbN based device consists of an ultrathin (4 nm), 100 nm wide NbN nanowire patterned with electron beam lithography out of a superconductor film (fig a) having a critical temperature around 10-12K. The superconducting nanowire is arranged in meander geometry in order to achieve high coupling efficiency between the detector active area (typically 10x10 um2) and the optical beam of the source.
Improvement of the quantum efficiency are obtained fabricating the superconducting detector on top of a specifically designed optical λ/4-cavity made of SiO2 on a Si substrate. The silicon wafer is micro machined according to the procedure first proposed in 2011 at the NIST Boulder (fig. b and c) to get self alignment with an optical fiber.
The device, working in the temperature range 0.1-4K, is embedded in a microwave coplanar waveguide to read-out the fast electronic response to the optical source. The cryogenic system at IFN is based on a GM refrigerator and efficiently couples photons from SMF fibers to SNSPDs allowing the characterization of the single photon efficiency of the nanowired photosensitive material (fig d and e).
Thanks to their low timing jitter and their high-speed, SNSPDs have been widely implemented in quantum information application.