  Around forty years have passed since the first pioneering works have
introduced the possibility of using quantum physics to strongly enhance
communications safety. Nowadays Quantum Cryptography, and in particular,
Quantum Key Distribution (QKD) exited the physics laboratories to become
commercial technologies that increasingly trigger the attention of States,
military forces, banks, and private corporations. This work takes on the
challenge of bringing QKD closer to a consumer technology: optical fibers
deployed and used by telecommunication companies of different States have been
used to realize a quantum network, the first-ever connecting three different
countries. This pushes towards the necessary coexistence of QKD and classical
communications on the same infrastructure, which currently represents a main
limit of this technology. Our network connects Trieste to Rijeka and Ljubljana
via a trusted node in Postojna; a key rate of over 3 kbps has been achieved in
the shortest link, and a 7-hour long measurement has demonstrated the system
stability and reliability. Finally, the network has been used for a public
demonstration of QKD at the G20 Digital Ministers' Meeting in Trieste. The
reported experimental results, together with the significant interest that one
of the most important events of international politics has attracted, showcase
the maturity of the QKD technology bundle, placing it in the spotlight for
consumer applications in the near term.
