  Photonic quantum technology provides a viable route to quantum communication,
quantum simulation, and quantum information processing. Recent progress has
seen the realisation of boson sampling using 20 single-photons and quantum key
distribution over hundreds of kilometres. Scaling the complexity requires
architectures containing multiple photon-sources, photon-counters, and a large
number of indistinguishable single photons. Semiconductor quantum dots are
bright and fast sources of coherent single-photons. For applications, a
significant roadblock is the poor quantum coherence upon interfering single
photons created by independent quantum dots. Here, we demonstrate two-photon
interference with near-unity visibility ($93.0\pm0.8$)\% using photons from two
completely separate GaAs quantum dots. The experiment retains all the emission
into the zero-phonon-line -- only the weak phonon-sideband is rejected -- and
temporal post-selection is not employed. Exploiting the quantum interference,
we demonstrate a photonic controlled-not circuit and an entanglement with
fidelity ($85.0\pm 1.0$)\% between photons of different origins. The two-photon
interference visibility is high enough that the entanglement fidelity is well
above the classical threshold. The high mutual-coherence of the photons stems
from high-quality materials, a diode-structure, and the relatively large
quantum dot size. Our results establish a platform, GaAs QDs, for creating
coherent single photons in a scalable way.
