Single-photon detector for long-distance fiber-optic quantum key distribution

We have investigated the performance of an InGaAs/InP avalanche photodiode for photon counting at 1550 nm in the temperature range of thermoelectric cooling. A quantum efficiency of 13.7% was obtained at $-55 {}^{°}\mathrm{C}$, while the dark-count probability per gate $\left(\simeq 1 \mathrm{ns}\right)$ was kept as small as $2.4\times {10}^{-5}$. The developed single-photon detector would yield a 104.4-km fiber-optic quantum key distribution in the ideal condition.