  Single photonic applications - such as quantum key distribution - rely on the
transmission of single photons, and require the ultimate sensitivity that an
optical detector can achieve. Single-photon detectors must convert the energy
of an optical pulse containing a single photon into a measurable electrical
signal. We report on fiber-coupled superconducting single-photon detectors
(SSPDs) with specifications that exceed those of avalanche photodiodes (APDs),
operating at telecommunication wavelength, in sensitivity, temporal resolution
and repetition frequency. The improved performance is demonstrated by measuring
the intensity correlation function g(2)(t) of single-photon states at 1300nm
produced by single semiconductor quantum dots (QDs).
