Last year, the Faculty of Electrical Engineering and Communication of the Brno University of Technology opened a new Quantum Security Laboratory, where you can find equipment used to ensure communication resistant to attacks by quantum computers (find more details here). Now the scientists have transferred the quantum link from the laboratory environment to a real operational network connecting the Faculty of Electrical Engineering and Communication (FEEC) and the Faculty of Information Technology (FIT), i.e. two campuses located in different parts of Brno. This connection represents a further step towards building a quantum network and strengthening the cybersecurity research.

In addition to the aforementioned faculties, the university's rectorate as well as the Computing and Information Services Centre (CISC), which prepared a suitable route on the existing optical infrastructure, participated in the construction of the link. The new encrypted connection corresponds to a real installation and will primarily serve research and education.

"The entire implementation, including preparation, testing in laboratory conditions and subsequent installation on the operational network, took several weeks and a number of technical problems had to be solved. These were unique in the Czech Republic, and it was not possible to use a pre-prepared deployment scenario. This makes the whole installation and our experience gained during it quite unique," said Jan Hajný, the principal investigator of the research project.

A quantum link uses two fibres, i.e. two separate transmission paths, with one fibre currently used for quantum transmission and the other carrying the service channel. Since quantum transmission is significantly affected by the quality of the transmission path, the actual installation on a real network was preceded by lengthy testing in the laboratory simulating practical problems. The total length of the path is 7.5 km and contains a total of 6 connections on connectors that are not entirely ideal for quantum transmission.

"The service channel normally uses two separate fibers for bi-directional transmission, so it was necessary to integrate both directions into a single fiber. In order to be able to monitor both end units with its own monitoring system, it was also necessary to convert the data output on the FIT side to an optical signal and merge it into the same fiber with the service channel. In total, four channels are transmitted on the second fibre at different wavelengths," Hajný described the technical challenges the team had to overcome.

Further possibilities for the development of the BUT quantum network, including the building of a national quantum network and its connection to foreign nodes, are currently being discussed at the EU-SecRes international conference organized at BUT and MUNI, which is attended by cybersecurity specialists, representatives of quantum technology manufacturers and researchers from around the world.

The creation of a quantum link is one of the goals of the NESPOQ research project, which involves BUT, CESNET, VSB-TUO and NÚKIB (National Cyber and Information Security Agency) with the aim of verifying the functionality and applicability of quantum technologies in practice.