High-rate entanglement between a semiconductor spin and indistinguishable photons

Photonic graph states—quantum light states where multiple photons are mutually entangled—are key resources for optical quantum technologies. They are notably at the core of error-corrected measurement-based optical quantum computing and all-optical quantum networks. In the discrete variable framework, these applications require the high-efficiency generation of cluster states whose nodes are indistinguishable photons. Such photonic cluster states can be generated with heralded single-photon sources and probabilistic quantum gates, yet with challenging efficiency and scalability. Spin–photon entanglement has been proposed to deterministically generate linear cluster states. First demonstrations have been obtained with semiconductor spins, achieving high photon indistinguishability, and most recently with atomic systems with a high collection efficiency and record length. Here we report on the efficient generation of three-partite cluster states made of one semiconductor spin and two indistinguishable photons. We harness a semiconductor quantum dot inserted in an optical cavity for efficient photon collection and electrically controlled for high indistinguishability. We demonstrate two- and three-particle entanglement with fidelities of 80 ± 4% and 63 ± 5%, respectively, with photon indistinguishability of 88 ± 0.5%. Owing to the high operation rate allowed by the quantum-dot platform, the spin–photon and spin–photon–photon entanglement rates exceed, by three and two orders of magnitude, respectively, those of the previous state of the art. Our system and experimental scheme, a monolithic solid-state device controlled with a resource-efficient simple experimental configuration, are very promising for future scalable applications.