On the technology side, the project clearly demonstrated that photonic integration of key parts of quantum communication systems is possible. The project developed a 1 GHz QKD transmitter on chip. After packaging and integrating the chip with a FPGA based pattern generator, a full QKD key exchange cold eb demonstrated. Key generation rates of 800 bit/s per second and distances of up to 30 km were demonstrated. For CV-QKD, the UNIQORN team demonstrated an ultra-low noise amplifier with an electronic noise figure one thousand times smaller than the intrinsic noise of the light field. The amplifier was integrated further with an optical chip featuring a balanced detector assembly. Together they form a low noise receiver unit for coherent quantum communication devices. A hybrid integration method, combining a polymer chip for quantum random number generation with a silicon based single photon detector chip was also successfully demonstrated, paving the way for future lab-on-chip products. To simulate the performance of quantum communication devices, a full toolkit was developed that allows the user to “drag and drop” individual components and assemble them into full systems. The toolkit is capable to simulate components for DV and CV QKD as well as channel noise such as Raman scattering.
On the application side, several use-cases for QKD were identified ranging from securing 5G installations to fiber-to-the-home applications. To showcase the application of quantum communication in data centres, commercial network interface cards (NIC) were adapted to accept random numbers from a quantum random number generator. The integration with standard IPsec headers was demonstrated by implementing a Diffie-Hellman key exchange protocol that shares IPsec authentication and symmetric encryption keys between the two Bluefield NIC endpoints. The project studied a realistic Fiber-To-The-Home (FTTH) network serving up to 32 users. It was based on passive and active telecom equipment which is currently deployed in existing Gigabit Passive Optical Network (GPON)-based infrastructure, installed in the Athens metropolitan area. Three different FTTH scenarios were investigated with varying feeder and distribution lengths (up to a few kilometers). To demonstrate the readiness of QKD for deployment in fiber networks, a QKD key exchange could be demonstrated with classical data channels aggregating a power of 12 dBm using a novel hollow-core fibre type (7.7 km length). This result shows that strong classical data and quantum signals can be distributed simultaneously over the same fiber.
As an example of a non-QKD protocol, the use of quantum one-time programs was investigated, and a suitable use case was developed. This use case is centered around the use of photonic quantum states to represent one-time tokens. The protocol was successfully demonstrated over a deployed fiber with a trusted Token Service Provider distributing quantum states to a client, who measures the tokens in a set of bases that corresponds to a specific merchant ID.
