Figure 2

Fibre distance dependence.

Experimental secure bit rate as a function of fibre distance in the presence of 2 × 100 G forward directed classical data traffic over the same fibre (see Methods for details on the QKD protocol). Data is reported for two different filter widths, 100 GHz (blue circles) and 25 GHz (red circles). Corresponding sifted bit rates and quantum bit error rates are displayed as squares and triangles respectively. The solid and dashed lines are calculated using numerical simulation (see refs 8, 11 and 15 for more details). The simulation fully accounts for Raman forward scattering by the classical data traffic into the quantum channel. Error bar is two standard deviations. Effective fibre losses are shown on the top axis. Inset: Secure bit rate and data bit error rate (before forward error correction) for a duration of 2 hours at a fibre length of 101 km.