  An outstanding goal in quantum optics and scalable photonic quantum
technology is to develop a source that each time emits one and only one
entangled photon pair with simultaneously high entanglement fidelity,
extraction efficiency, and photon indistinguishability. By coherent two-photon
excitation of a single InGaAs quantum dot coupled to a circular Bragg grating
bullseye cavity with broadband high Purcell factor up to 11.3, we generate
entangled photon pairs with a state fidelity of 0.90(1), pair generation rate
of 0.59(1), pair extraction efficiency of 0.62(6), and photon
indistinguishability of 0.90(1) simultaneously. Our work will open up many
applications in high-efficiency multi-photon experiments and solid-state
quantum repeaters.
