Deterministic photon source of genuine three-qubit entanglement

TL;DR

This paper demonstrates a deterministic, scalable source of three-qubit entanglement using a single electron spin in a quantum dot embedded in a nanophotonic waveguide, advancing quantum photonic technologies.

Contribution

It introduces a method for generating high-fidelity three-qubit entanglement from a single quantum emitter with improved spin coherence and photon indistinguishability.

Findings

Achieved nuclear spin narrowing to extend spin dephasing time to ~33 ns.

Implemented spin-echo sequences for sequential entanglement generation.

Produced highly indistinguishable photons suitable for photon fusion.

Abstract

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 $T_2^* \simeq 33$ ns, which enables high-fidelity coherent optical spin rotations, and realize a spin-echo pulse sequence for sequential generation of high-fidelity spin-photon and spin-photon-photon entanglement. The emitted photons are highly indistinguishable, which is a key requirement for 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.