  In view of real world applications of quantum information technologies, the
combination of miniature quantum resources with existing fibre networks is a
crucial issue. Among such resources, on-chip entangled photon sources play a
central role for applications spanning quantum communications, computing and
metrology. Here, we use a semiconductor source of entangled photons operating
at room temperature in conjunction with standard telecom components to
demonstrate multi-user quantum key distribution, a core protocol for securing
communications in quantum networks. The source consists of an AlGaAs chip
emitting polarization entangled photon pairs over a large bandwidth in the main
telecom band around 1550 nm without the use of any off-chip compensation or
interferometric scheme; the photon pairs are directly launched into a dense
wavelength division multiplexer (DWDM) and secret keys are distributed between
several pairs of users communicating through different channels. We achieve a
visibility measured after the DWDM of 87% and show long-distance key
distribution using a 50-km standard telecom fibre link between two network
users. These results illustrate a promising route to practical,
resource-efficient implementations adapted to quantum network infrastructures.
