https://www.scientificamerican.com/article/physicists-create-city-sized-ultrasecure-quantum-network/

Quantum cryptography promises a future in which computers communicate with one another over ultrasecure links using the razzle-dazzle of quantum physics. But scaling up the breakthroughs in research labs to networks with a large number of nodes has proved difficult. Now an international team of researchers has built a scalable city-wide quantum network to share keys for encrypting messages.

The network can grow in size without incurring an unreasonable escalation in the costs of expensive quantum hardware. Also this system does not require any node to be trustworthy, thus removing any security-sapping weak links.