Fernando Melo

This work introduces a metropolitan quantum communication network connecting four research institutions in the state of Rio de Janeiro through installed dark optical fibers and a 7-km free space link. The Twin-Field Measurement Device Independent Quantum Key Distribution (TF-MDI-QKD) protocol is implemented to enable secure communication between any two network nodes independently, without the need for trusted nodes. The proposed structured - a "folded Sagnac" configuration - is shown to be able to not only automatically compensate for phase fluctuations but also circumvent unneeded losses by reconfiguring the Sagnac loop size as needed; moreover, by employing polarization control and a Faraday Mirror, the free-space link can be added to the loop without the need for additional telescopes. The first experimental results will be presented together with the main engineering challenges being tackled.