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We present a 625 MHz clocked coherent one-way quantum key distribution (QKD) system which continuously distributes secret keys over an optical fibre link. To support high secret key rates, we implemented a fast hardware key distillation engine which allows for key distillation rates up to 4 Mbps in real time. The system employs wavelength multiplexing in order to run over only a single optical fibre and is compactly integrated in 19-inch 2U racks. We optimized the system considering a security analysis that respects finite-key-size effects, authentication costs, and system errors. Using fast gated InGaAs single photon detectors, we reliably distribute secret keys with rates up to 140 kbps and over 25 km of optical fibre, for a security parameter of 4E-9.

We present and analyze a gated single photon avalanche detector using a sine gating scheme with a simple but effective low-pass filtering technique for fast low-noise single photon detection at telecom wavelength. The detector is characterized by 130 ps short gates applied with a frequency of 1.25 GHz, yields only 70 ps timing jitter and noise probabilities as low as 7E-7 per gate at 10% detection efficiency. We show that the detector is suitable for high rate quantum key distribution (QKD) and even at room temperature it could allow for QKD over distances larger than 25 km., Comment: 6 pages, 11 figures

InGaAs/InP-based semiconductor avalanche photodiode are usually employed for single-photon counting at telecom wavelength. However they are affected by afterpulsing which limits the diode performance. Recently, Princeton Lightwave has commercialised a diode integrating monolithically a feedback resistor. This solution effectively quenches the avalanche and drastically reduces afterpulsing. Here, we report the development and characterization of a detector module based on this diode, implementing an active hold-off circuit which further reduces the afterpulsing and notably improves the detector performances. We demonstrate free-running operation with 600 Hz dark count rate at 10% detection efficiency. We also improved the standard double-window technique for the afterpulsing characterization. Our algorithm implemented by a FPGA allows to put the APD in a well-defined initial condition and to measure the impact of the higher order afterpulses., Comment: 18 pages, 15 figures. Submitted to Journal of Modern Optics

A physical random number generator based on the intrinsic randomness of quantum mechanics is described. The random events are realized by the choice of single photons between the two outputs of a beamsplitter. We present a simple device, which minimizes the impact of the photon counters' noise, dead-time and after pulses., Comment: 3 pages + 1 figure

Some guidelines for the comparison of different quantum key distribution experiments are proposed. An improved 'plug & play' interferometric system allowing fast key exchange is then introduced. Self-alignment and compensation of birefringence remain. Original electronics implementing the BB84 protocol and allowing user-friendly operation is presented. Key creation with 0.1 photon per pulse at a rate of 486 Hz with a 5.4% QBER - corresponding to a net rate of 210Hz - over a 23 Km installed cable was performed., Comment: 21 pages, 6 figures, added reference