  Entangled photon sources with simultaneously near-unity heralding efficiency
and indistinguishability are the fundamental elements for scalable photonic
quantum technologies. We design and realize a degenerate entangled-photon
source from an ultrafast pulsed laser pumped spontaneous parametric
down-conversion (SPDC), which show simultaneously ~97% heralding efficiency and
~96% indistinguishability between independent single photons. Such a
high-efficiency and frequency-uncorrelated SPDC source allows generation of the
first 12-photon genuine entanglement with a state fidelity of 0.572(24). We
further demonstrate a blueprint of scalable scattershot boson sampling using 12
SPDC sources and a 12*12-modes interferometer for three-, four-, and five-boson
sampling, which yields count rates more than four orders of magnitudes higher
than all previous SPDC experiments. Our work immediately enables
high-efficiency implementations of multiplexing, scattershot boson sampling,
and heralded creation of remotely entangled photons, opening up a promising
pathway to scalable photonic quantum technologies.
