In this paper, we present the architecture and results of the SwissQuantum quantum key distribution (QKD) network.
This three nodes triangular quantum network was running from March 2009 to January 2011 in the Geneva metropolitan
area. The three trusted nodes were located at the University of Geneva (Unige), the CERN and the University of Applied
Sciences Western Switzerland in Geneva (hepia Geneva). This quantum network was deployed to prove reliability of
QKD in telecommunication network over a long period. To facilitate integration of QKD in telecommunication network,
this quantum network was composed of three layers: a quantum layer, a key management layer, and an application layer.
The keys are distributed in the first layer; they are handled in the second layer; and they are used in the third layer.
We implement an InGaAs/InP single-photon avalanche diode (SPAD) for single-photon detection with the fastest
gating frequency reported so far, of 2.23GHz, which approaches the limit given by the bandwidth of the SPAD
- 2.5 GHz. We propose a useful way to characterize the afterpulsing distribution for rapid gating that allows for
easy comparison with conventional gating regimes. We compare the performance of this rapid gating scheme with
free-running detector and superconducting single-photon detector (SSPD) for the coherent one-way quantum key
distribution (QKD) protocol. The rapid gating system is well suited for both high-rate and long-distance QKD
applications, in which Mbps key rates can be achieved for distances less than 40km with 50 ns deadtime and the
maximum distance is limited to ~190km with 5 μs deadtime. These results illustrate that the afterpulsing is no
longer a limiting factor for QKD.
We implement an OTDR with photon-counting modules at 1550nm based on sum frequency generation in a PPLN waveguide. The narrow temporal response of those detectors allows achieving a 2-points resolution of few centimetres.
A compact single photon detector designed for the detection in the visible spectral range is presented. A fast active quenching circuit is integrated on the chip in order to operate the APD in single photon counting mode. The sensor consists of a 0.8x0.8mm<sup>2</sup> silicon chip mounted on a thermo-electric cooler and packaged in a standard TO5 header, bringing the degree of miniaturization to a level never reached. Reliability, compactness, low power and low cost make the detector essential for portable devices, implantable sensors, fluorescence lifetime spectrometers or laser scanning microscopes. In addition, the sensor exhibits best-in-class timing resolution of 50ps. The photon detection probability peaks in the blue/green at almost 35% and is limited to a few percents in the red and near-infrared regions. When cooled down to -10°C, the 50μm diameter diode achieves a dark count rate lower than 10Hz. The afterpulsing is maintained to a low level, below 1%. The fast active quenching circuit leads to a dead time of 50ns allowing a measurement frequency of up to 20MHz. The detector, unlike legacy photon counters, does not suffer from memory effects and is not damaged by ambient light.