  Entanglement-based quantum key distribution promises enhanced robustness
against eavesdropping and compatibility with future quantum networks. Among
other sources, semiconductor quantum dots can generate polarization-entangled
photon pairs with near-unity entanglement fidelity and a multi-photon emission
probability close to zero even at maximum brightness. These properties have
been demonstrated under resonant two-photon excitation (TPE) and at operation
temperatures between 4 and 8 K. However, source blinking is often reported
under TPE conditions, limiting the maximum achievable photon rate. In addition,
operation temperatures reachable with compact cryo-coolers could facilitate the
widespread deployment of quantum dots, e.g. in satellite-based quantum
communication. Here we demonstrate blinking-free emission of highly entangled
photon pairs from GaAs quantum dots embedded in a p-i-n diode. High fidelity
entanglement persists at temperatures of at least 20 K, which we use to
implement fiber-based quantum key distribution between two building with an
average key rate of 55 bits/s and a qubit error rate of 8.4%. We are confident
that by combining electrical control with already demonstrated photonic and
strain engineering, quantum dots will keep approaching the ideal source of
entangled photons for real world applications.
