  State-of-the-art Superconducting Nanowire Single Photon Detectors based on
low-Tc materials reach 100% quantum efficiency. However, the response time is
limited to >1-10 ns. Recently, it has been shown that due to a much lower
kinetic inductance, a 100 ps response rate can be achieved in 120 $\mu$m-long
$MgB_{2}$ nanowires. In this work, we demonstrate experimentally that such
$MgB_{2}$ nanowires function as single-photon detectors for both visible
($\lambda$= 630 nm) and infrared ($\lambda$= 1550 nm) photons when biased close
to the critical current, with a dark count rate of <10 cps. $MgB_{2}$
photodetectors over-perform NbN SNSPDs in speed by at least an order of
magnitude for similar nanowire lengths. Such photodetectors offer a platform
for single-photon detectors with a long thought-after combination of a large
detector area and a response rate of up to 10 GHz with a single readout line.
