  Quantum key distribution---exchanging a random secret key relying on a
quantum mechanical resource---is the core feature of secure quantum networks.
Entanglement-based protocols offer additional layers of security and scale
favorably with quantum repeaters, but the stringent requirements set on the
photon source have made their use situational so far. Semiconductor-based
quantum emitters are a promising solution in this scenario, ensuring on-demand
generation of near-unity-fidelity entangled photons with record-low
multi-photon emission, the latter feature countering some of the best
eavesdropping attacks. Here we first employ a quantum dot to experimentally
demonstrate a modified Ekert quantum key distribution protocol with two quantum
channel approaches: both a 250 meter long single mode fiber and in free-space,
connecting two buildings within the campus of Sapienza University in Rome. Our
field study highlights that quantum-dot entangled-photon sources are ready to
go beyond laboratory experiments, thus opening the way to real-life quantum
communication.
