  The distribution of entanglement via satellite links will drastically extend
the reach of quantum networks. Highly efficient entangled photon sources are an
essential requirement towards overcoming high channel loss and achieving
practical transmission rates in long-distance satellite downlinks. Here we
report on an ultrabright entangled photon source that is optimized for
long-distance free-space transmission. It operates in a wavelength range that
is efficiently detected with space-ready single photon avalanche diodes
(Si-SPADs), and readily provides pair emission rates that exceed the detector
bandwidth (i.e., the temporal resolution). To overcome this limitation, we
demultiplex the photon flux into wavelength channels that can be handled by
current single photon detector technology. This is achieved efficiently by
using the spectral correlations due to hyper-entanglement in polarization and
frequency as an auxiliary resource. Combined with recent demonstrations of
space-proof source prototypes, these results pave the way to a broadband
long-distance entanglement distribution network based on satellites.
