  We report the first real world implementation of a Quantum Key Distribution
(QKD) system over a 43dB-loss transmission line in the Swisscom fibre optic
network. The QKD system is capable of continuous and autonomous operation and
uses the coherent one-way (COW) protocol. This system brings together three key
concepts for future QKD systems: a simple high-speed protocol; high performance
detection; and integration, both at the component level as well for
connectivity with standard fibre networks. Here, we show laboratory and field
trial results for this system. The full prototype version uses InGaAs/InP
avalanche photodiodes (APDs) and was laboratory tested up to 150km, with a
10-hour exchange averaging around 2kbps of real-time distilled secret bits over
100km. In the field trials, we obtained average distribution rates, during 3
hours, of 2.5bps over a 43dB-loss line of 150km, when using superconducting
single photon detectors (SSPDs).
