Quantum technologies are the main topic of more research projects than ever within the scientific community. The most mature examples of such technologies, in terms of commercialisation, are quantum key distribution (QKD) and quantum random number generators (QRNGs). At this point in their development, academia and industry are interested in a scalable, reliable and cheap production of such systems, which is where the usage of integrated photonic circuits (PICs) come in handy.

First, I will present the development of two fibre-based QKD systems, based on a simplified QKD protocol 1, which I took part in during my thesis. One system was implemented to operate in combination with classical communication through the usage of wavelength division multiplexing. The other one was made to achieve as high secret key rate as possible, achieved by employing multipixel superconducting nanowire single-photon detectors, among other improvements.

Secondly, the primary focus of my work, which resides in the development and implementation of a QKD system based on integrated photonics, using the simplified QKD protocol, will be presented. On the transmitter side, a silicon photonics PIC was developed and manufactured in close collaboration with IDQ SA and Sicoya GmbH. The PIC, when used with an external laser, allows for high-speed and accurate state preparation. On the receiver side, two distinct integrated photonic platforms were investigated. One was based on silica on silicon, established in collaboration with VLC photonics and the other one was based on silica, established in collaboration with the Institute for Photonics and Nanotechnologies (IFN) in Milano. The silica PIC was employed for the final integrated QKD setup thanks to its low loss and polarisation independence. Full secret key exchanges over hundreds of kilometers of single-mode fibre between the transmitter and receiver were performed, employing either superconducting nanowire single-photon detectors or single-photon avalanche diodes. The corresponding secret key rates obtained with the aforementioned detectors are 9.4 kbps over 202 km and 1.3 kbps over 151.5 km, respectively.

Finally, I introduce a recent project of my thesis, namely, the implementation of a QRNG in an integrated circuit. The QRNG is based on a self-testing protocol employing homodyne detection. We developed a PIC based on indium phosphide in collaboration with HHI Fraunhofer, which includes all the optics of the experimental setup. Investigations are currently ongoing and I will in this manuscript present the developed electronics, the schematics of the chip as well as some preliminary characterisations.