Superconducting nanowire single-photon detectors (SNSPD), thanks to their unparalleled efficiency and time resolution, are the leading single-photon detection technology. The efficiency of SNSPDs has recently approached unity and it has also been proven that the detectors’ time resolution can be better than 3 ps.
At TU Delft Iman Esmaeil Zadeh and his colleagues have been developing the detectors and working with these since 2011: fabricating them in the Kavli cleanroom, and measuring their performance. After receiving a small funding from CERN to develop particle detectors and later from a spin off company, devices were sold to scientists and other industries.
The working principle of an SNSPD is based on transition of a current-biased superconducting nanowire into normal metal following absorption of a particle/single-photon in the following steps: initially a non-superconducting section is formed which forces the current to go around its sidewalks, this in turn causes the critical current density in those regions to exceed the critical value and therefore a resistive area is formed across the nanowire. The resistive region then expands (Joule heating) and pushes the current away from the nanowire into the readout circuitry, cooling it down so that it recovers its superconductivity and can detect again. SNSPDs are normally operated well below their critical temperature in the range of 800 mK-4 K. Conventional nanowires are about 500 µm long and are folded (meandering) over an area of ~10×10 µm2.
SNSPDs can be conveniently and efficiently integrated with dielectric waveguides on-chip therefore they hold great promises for future [quantum] nanophotonics technologies. The time resolution of SNSPD is also great advantage for example to erase small photon “distinguishabilities” (quantum erasure). In addition SNSPDs have a very broadband internal response being sensitive to energetic particles, X-ray, and visible and infrared photons. Arrays of SNSPDs have been recently developed which can be used in imaging and spectroscopic applications. Such high performance arrays hold great prospect in the fields of quantum optics, high energy physics, and mid-infrared spectroscopy.