Deterministic photon source of genuine three-qubit entanglement

Deterministic photon sources allow long-term advancements in quantum optics.A single quantum emitter embedded in a photonic resonator or waveguide may be triggered to emit one photon at a time into a desired optical mode.By coherently controlling a single spin in the emitter, multi-photon entanglement can be realized.We demonstrate a deterministic source of three-qubit entanglement based on a single electron spin trapped in a quantum dot embedded in a planar nanophotonic waveguide.We implement nuclear spin narrowing to increase the spin dephasing time to T * 2 ≃ 33 ns, which enables high-fidelity coherent optical spin rotations, and realize a spin-echo pulse sequence for sequential generation of spin-photon and spin-photon-photon entanglement.The emitted photons are highly indistinguishable, which is a key requirement for scalability and enables subsequent photon fusions to realize larger entangled states.This work presents a scalable deterministic source of multi-photon entanglement with a clear pathway for further improvements, offering promising applications in photonic quantum computing or quantum networks.