<\/a>Figure 1: Detection efficiency (\u03b7) of a 30 nm width SNSPD as a function of normalized bias current (IB\/Isw) measured at wavelength \u03bb = 1.4 \u00b5m (blue curve), \u03bb = 3.7 \u00b5m (red curve), and \u03bb = 5 \u00b5m (black curve).<\/p><\/div>\n
We report on the detection of single-photons in the middle-infrared (mid\u2011IR) range using superconducting nanowire single-photon detectors (SNSPDs). In 2011 our group managed to detect single-photons at a wavelength \u03bb<\/em>\u00a0=\u00a01.55\u00a0\u00b5m using SNSPDs based on ultra-narrow nanowires (30\u2011nm\u2011width) with a saturated detection efficiency of \u03b7<\/em>\u00a0=\u00a020\u00a0% at a lower bias current than is possible for wider NbN nanowires[1] (I<\/em>B<\/sub>\u00a0=\u00a00.7\u00a0I<\/em>sw<\/sub>, where I<\/em>sw<\/sub> is the bias current after which the detectors switch to the normal state). These results suggest that ultra-narrow SNSPDs are suitable for detection of photons at longer wavelengths. Figure 1 shows the detection efficiency \u03b7<\/em> measured as a function of the normalized bias current (I<\/em>B<\/sub>\/I<\/em>sw<\/sub>) for \u03bb<\/em>\u00a0=\u00a01.4\u00a0\u00b5m (blue curve), \u03bb<\/em>\u00a0=\u00a03.6\u00a0\u00b5m (red curve), and \u03bb<\/em>\u00a0=\u00a05\u00a0\u00b5m (black curve). The detection efficiency measured at \u03bb<\/em>\u00a0=\u00a01.4\u00a0\u00b5m does not reach \u03b7<\/em>\u00a0=\u00a020\u00a0% because the polarization of the photons could not be optimized to enhance the absorption in the nanowires as in reference [