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arXiv:2410.23518 · Nature Communications

Deterministic and reconfigurable graph state generation with a single solid-state quantum emitter

Hêlio Huet, Polluri Ramesh, Stephen C. Wein, Nathan Coste, Paul Hilaire, Niccolò Somaschi, Martina Morassi, Aristide Lemaître, Isabelle Sagnes, Matthew F. Doty, O. Krebs, L. Lanco, Dario Fioretto, P. Senellart

Published May 9, 2025• 27 citations
arXivHTMLPDF

Abstract

Measurement-based quantum computing offers a promising route towards scalable, universal photonic quantum computation. This approach relies on the deterministic and efficient generation of photonic graph states in which many photons are mutually entangled with various topologies. Recently, deterministic sources of graph states have been demonstrated with quantum emitters in both the optical and microwave domains. In this work, we demonstrate deterministic and reconfigurable graph state generation with optical solid-state integrated quantum emitters. Specifically, we use a single semiconductor quantum dot in a cavity to generate caterpillar graph states, the most general type of graph state that can be produced with a single emitter. By using fast detuned optical pulses, we achieve full control over the spin state, enabling us to vary the entanglement topology at will. We perform quantum state tomography of two successive photons, measuring Bell state fidelities up to 0.80 ± 0.04 and concurrences up to 0.69 ± 0.09, while maintaining high photon indistinguishability. This simple optical scheme, compatible with commercially available quantum dot-based single photon sources, brings us a step closer to fault-tolerant quantum computing with spins and photons. Quantum emitters have recently been identified as efficient sources of graph states, which are entangled states crucial for photonic quantum computation. Here the authors demonstrate deterministic and reconfigurable generation of caterpillar graph states using a semiconductor quantum dot in a cavity.

DOI
10.1038/s41467-025-59693-3

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Measurement-based quantum computing offers a promising route towards scalable, universal photonic quantum computation. This approach relies on the deterministic and efficient generation of photonic graph states in which many photons are mutually entangled with various topologies. Recently, deterministic sources of graph states have been demonstrated with quantum emitters in both the optical and microwave domains. In this work, we demonstrate deterministic and reconfigurable graph state generation with optical solid-state integrated quantum emitters. Specifically, we use a single semiconductor quantum dot in a cavity to generate caterpillar graph states, the most general type of graph state that can be produced with a single emitter. By using fast detuned optical pulses, we achieve full control over the spin state, enabling us to vary the entanglement topology at will. We perform quantum state tomography of two successive photons, measuring Bell state fidelities up to 0.80 ± 0.04 and concurrences up to 0.69 ± 0.09, while maintaining high photon indistinguishability. This simple optical scheme, compatible with commercially available quantum dot-based single photon sources, brings us a step closer to fault-tolerant quantum computing with spins and photons. Quantum emitters have recently been identified as efficient sources of graph states, which are entangled states crucial for photonic quantum computation. Here the authors demonstrate deterministic and reconfigurable generation of caterpillar graph states using a semiconductor quantum dot in a cavity.
Quantum computation using photons offers one possible route towards the long-standing goal of scalable, fault-tolerant quantum computing. Within this realm, measurement-based quantum computing offers a promising approach exploiting many of the advantages of photons. Implementing photonic measurement-based architectures relies upon the deterministic generation of graph states composed of many entangled photons. Semiconductor quantum dots (QDs) are sources of indistinguishable single photons and hosts of solid-state spins, marking them desirable platforms for controlled entanglement generation. Such a platform consisting of a single charged QD coupled to a photonic cavity has been proven for the generation of multipartite spin-photon graph states. This dissertation will present advancements in the versatility and coherence of such entanglement generation. First, background on quantum dots, single photon generation, spin control, and entanglement will be introduced. Then, sources of error and decoherence will be addressed using control of the hole g-factor and dynamical decoupling techniques. The aim of versatility is advanced through results on the generation of four-partite graph states with on-demand reconfigurability of the type of state produced. Finally, a different paradigm using quantum dot molecules will be introduced, and novel estimation of important physical parameters in this system is developed.
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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 T2∗≃33{T}_{2}^{*}\simeq 33T2∗​≃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. Entanglement between single photons and solid-state emitters is a key component for photonic quantum computing and networks. Here, using a single electron spin in a quantum dot, the authors present a deterministic photon source achieving three-qubit entanglement of one electron spin and two photons.