Parallel to our efforts in free-space quantum communication, we are adapting our know-how to fiber-based communication schemes. These are important to build network structures that connect several users at once, running continuously 24/7. For the long-term goal of a quantum internet, local quantum networks are an important addition to free-space satellite links.
A Colorful Network
The simultaneous distribution of entanglement between four different users was a breakthrough in quantum communications. This experiment, in which we used color and timing correlations of a broad-band photon pair source, made it to the cover of Nature magazine in December 2018 . In a collaboration with the University of Bristol, we have extended this experiment to 8 users .
Entanglement between Sicily and Malta
This large-scale demonstration of entanglement distribution via glass fibers was conducted in a real-world scenario. Using efficient nanowire detectors, we showed that telecom fibers are stable enough to carry polarization-entangled photons without destroying their quantum properties .
One of the most ambitious projects of the Ursin group is the establishment of a fiber-based European quantum network. The QUAntum Photonic Intercity TrAnsmission Lattice (QUAPITAL) aims to connect metropolitan areas via readily deployed telecom fibers. The first connection between Vienna and Bratislava will open by 2020. For news check quapital.eu.
 S. Wengerowsky et al., “An entanglement-based wavelength-multiplexed quantum communication network”, Nature, Vol. 564, pp. 225-228, Dec. 2018
 S. K. Joshi et al., prep., 2019
 S. Wengerowsky et al., “Entanglement distribution over a 96-km-long submarine optical fiber,” Proc. Natl. Acad. Sci., vol. 116, no. 14, pp. 6684–6688, Apr. 2019.