In the previous decades quantum technologies have made a leap forward leaving the laboratories and entering the market, above all the technologies of quantum random number generators and quantum key distribution (QKD). This thesis focuses on the performance of high-speed QKD, showing what can be achieved with systems comprising of mainly commercially available components. During this work, I investigated three different aspects of such implementations.

First, I worked on the implementation of a polarization-based 3-state BB84 protocol at a qubit repetition rate of 5 GHz, with the focus on potential security threads due to correlations in its state preparation. I characterized these imperfections and performed secret key exchanges over 151.5 km, achieving a secret key rate of 54.5 kbps.

Secondly, I investigated the network integration of a high-speed QKD system. I worked on the implementation of a time-bin protocol developed in our group at a qubit repetition rate of 2.5 GHz. This system with quantum channel wavelength of 1310 nm was integrated in a network environment and I studied its performance. It has been found that it can exchange secret keys over a distance of 95.5 km in the presence of co-propagating classical channels with a total launch power of 8.9 dBm. I also studied previous network integration experiments and described which QKD system is suited best for a certain network environment.

Thirdly, I worked on maximizing the secret key rate of the above mentioned time-bin protocol, this time at a wavelength of 1551 nm. I optimized the detection electronics, which was then used with a 14-pixel superconducting nanowire single-photon detector designed within the research group. I focused on the fabrication of constant-fraction discriminators to improve the timing jitter of the detector pulse readout.The improved detection electronics enabled us to use the 14-pixel detector at full potential. I performed a secret key exchange with this system where a quantum bit error rate of 0.4% was achieved at a sifted key rate of 159.4 Mbps over 10 km of ultra-low-loss single-mode fiber, leading to a secret key rate of 63.6 Mbps.