  We demonstrate a high-accuracy distributed fiber-optic temperature sensor
using superconducting nanowire single-photon detectors and single-photon
counting techniques. Our demonstration uses inexpensive single-mode fiber at
standard telecommunications wavelengths as the sensing fiber, which enables
extremely low-loss experiments and compatibility with existing fiber networks.
We show that the uncertainty of the temperature measurement decreases with
longer integration periods, but is ultimately limited by the calibration
uncertainty. Temperature uncertainty on the order of 3 K is possible with
spatial resolution of the order of 1 cm and integration period as small as 60
seconds. Also, we show that the measurement is subject to systematic
uncertainties, such as polarization fading, which can be reduced with a
polarization diversity receiver.
