  Quantum communication has seen rapid progress towards practical large-scale
networks, with quantum key distribution (QKD) spearheading this development.
While fibre based systems have been shown to be well suited for metropolitan
scales, suitable fibre infrastructure may not always be in place. Here, we make
the case for an entanglement-based free-space quantum network as a practical
and efficient alternative for metropolitan applications. We developed a
deployable free space QKD system and demonstrated its use in realistic
scenarios. For a representative 1.7-km free-space link, we showcase its ad hoc
deployability and achieve secure key rates of up to 5.7 kbps, with 2.5 kbps in
direct noon sunlight. By extrapolating experimental data, we show that kbps key
rates are achievable even for 10-km distances and multi-user scenarios. We
anticipate that our work will establish free space networks as a viable
solution for metropolitan applications and an indispensable complementary
building block in the future global quantum internet.
