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arXiv:2602.03296 · npj Quantum Information

Decoherence-protected entangling gates in a silicon carbide quantum node

Shuo Ren, Rui-Jian Liang, Zhen-Xuan He, Ji-Yang Zhou, Wu-Xi Lin, Zhi-He Hao, Bing Chen, Tao Tu, Jin-Shi Xu, Chuan-Feng Li, Guang-Can Guo

quant-phSubmitted Feb 3, 2026• Announced Feb 4, 2026• 0 citations
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Abstract

Solid-state color centers are promising candidates for nodes in quantum network architectures. However, realizing scalable and fully functional quantum nodes, comprising both processor and memory qubits with high-fidelity universal gate operations, remains a central challenge in this field. Here, we demonstrate a fully functional quantum node in silicon carbide, where electron spins act as quantum processors and nuclear spins serve as quantum memory. Specifically, we design a pulse sequence that combines dynamical decoupling with hyperfine interactions to realize decoherence-protected universal gate operations between the processor and memory qubits. Leveraging this gate, we deterministically prepare entangled states within the quantum node, achieving a fidelity of 90%, which exceeds the fault-tolerance threshold of certain quantum network architectures. These results open a pathway toward scalable and fully functional quantum nodes based on silicon carbide.

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Solid-state color centers are promising candidates for nodes in quantum network architectures. However, realizing scalable and fully functional quantum nodes, comprising both processor and memory qubits with high-fidelity universal gate operations, remains a central challenge in this field. Here, we demonstrate a fully functional quantum node in silicon carbide, where electron spins act as quantum processors and nuclear spins serve as quantum memory. Specifically, we design a pulse sequence that combines dynamical decoupling with hyperfine interactions to realize decoherence-protected universal gate operations between the processor and memory qubits. Leveraging this gate, we deterministically prepare entangled states within the quantum node, achieving a fidelity of 90%, which exceeds the fault-tolerance threshold of certain quantum network architectures. These results open a pathway toward scalable and fully functional quantum nodes based on silicon carbide.
A distributed quantum network would require quantum nodes capable of performing arbitrary quantum information protocols with high fidelity. So far the challenge has been in realizing such quantum nodes with features for scalable quantum computing. We show here that using the solid-state spins in 4H-Silicon Carbide (4H-SiC) such a goal could be realized, wherein a controlled generation of highly coherent qubit registers using nuclear spins is possible. Using a controlled isotope concentration and coherent control we perform here atomistic modeling of the central spin system formed by the electron spin of a silicon vacancy color center (VSi−V_{Si}^-VSi−​-center) and the non-interacting nuclear spins. From this we lay out conditions for realizing a scalable nuclear-spin (13C^{13}C13C or 29Si^{29}Si29Si) register, wherein independent control of the qubits alongside their mutual controlled operations using the central electron spin associated to the VSi−V_{Si}^-VSi−​-center in 4H-SiC are achieved. Further, the decoherence and entanglement analysis provided here could be used to evaluate the quantum volume of these nodes. Our results mark a clear route towards realizing scalable quantum memory nodes for applications in distributed quantum computing networks and further for quantum information protocols.
Robust entanglement at room temperature is a central challenge for solid-state quantum information processing and quantum-enhanced sensing. Here we demonstrate room-temperature storage of entanglement in a silicon carbide (SiC) quantum node by coherently transferring an electron-nuclear entangled state onto long-lived nuclear-spin memory qubits. Using a shallow single color center in 4H-SiC, conventionally denoted PL6, we realize a fully addressable three-qubit register composed of one electron-spin processor and two strongly coupled 29^{29}29Si nuclear-spin memory qubits. This platform enables the deterministic generation of high-fidelity entangled states, including a nuclear-spin Bell state with a fidelity of 94±2%94 \pm 2\%94±2% and a three-qubit Greenberger-Horne-Zeilinger (GHZ)-type state with a fidelity of 89±4%89 \pm 4\%89±4%. By implementing a SWAP-gate protocol in the strong hyperfine-coupling regime, the electron-nuclear entanglement is transferred to the nuclear-spin memory with a fidelity of 92.5±2.5%92.5 \pm 2.5\%92.5±2.5%, extending the entanglement lifetime by a factor of 240. We further confirm the generality of this approach in an additional heterogeneous 29^{29}29Si-13^{13}13C nuclear-spin register and, through a statistical survey of 200 single PL6 centers, show that multi-nuclear-spin registers occur naturally with probabilities above 10%. These results position shallow SiC color centers as a powerful platform for entanglement-assisted quantum sensing and scalable room-temperature quantum technologies.
The ultimate motivation of my project is to address the possibility of building a quantum analogue of Internet of Things in order to improve the standards of quantum information processing. A distributed quantum computing network which is capable of achieving this goal, would require large sets of memory nodes capable of performing arbitrary quantum information protocols with high fidelity [1], [2]. So far, the challenge in this field has been in realizing such quantum memory nodes with features for scalable quantum computing. Solid state spins in 4H-Silicon Carbide (4H-SiC) owing to its material properties provides a suitable platform in achieving this goal wherein a controlled generation of highly coherent qubit registers using nuclear spins(13C or 29Si)(^{13}\mathrm{C} \ \text{or} \ {}^{\text{29}} \text{Si})(13C or 29Si)and silicon vacancy color centers(VSi− center)(V_{Si}^{-} \ \text{center})(VSi−​ center)| are possible[3], [4]. The magnetic dipole-dipole coupling between the isotope nuclear spins and the silicon vacancy color center can be tapped using microwave pulse (MW) sequence (as shown in Fig. 1(a)) for controlled driving of nuclear spin.
A distributed quantum network requires versatile and high-fidelity quantum memory nodes, but it remains challenging to make them scalable. This study investigates the use of multiple controllable quantum memories in silicon carbide---an established semiconductor material platform for various quantum technology applications---and provides a viable solution. The authors show that solid-state spins in silicon carbide are ideal quantum memories in a distributed quantum computing network, wherein a controlled generation of highly coherent qubit registers using nuclear spins is possible. This study will impact the future development of quantum networks with solid states spins as quantum memories.
Spins associated to solid-state color centers are a promising platform for investigating quantum computation and quantum networks. Recent experiments have demonstrated multiqubit quantum processors, optical interconnects, and basic quantum error-correction protocols. One of the key open challenges towards larger-scale systems is to realize high-fidelity universal quantum gates. In this work, we design and demonstrate a complete high-fidelity gate set for the two-qubit system formed by the electron and nuclear spin of a nitrogen-vacancy center in diamond. We use gate set tomography (GST) to systematically optimize the gates and demonstrate single-qubit gate fidelities of up to 99.999 ( 1 ) % and a two-qubit gate fidelity of 99.93 ( 5 ) % . Our gates are designed to decouple unwanted interactions and can be extended to other electron-nuclear spin systems. The high fidelities demonstrated provide opportunities towards larger-scale quantum processing with color-center qubits.
Long-distance quantum communication and networking require quantum memory nodes with efficient optical interfaces and long memory times. We report the realization of an integrated two-qubit network node based on silicon-vacancy centers (SiVs) in diamond nanophotonic cavities. Our qubit register consists of the SiV electron spin acting as a communication qubit and the strongly coupled silicon-29 nuclear spin acting as a memory qubit with a quantum memory time exceeding 2 seconds. By using a highly strained SiV, we realize electron-photon entangling gates at temperatures up to 1.5 kelvin and nucleus-photon entangling gates up to 4.3 kelvin. We also demonstrate efficient error detection in nuclear spin-photon gates by using the electron spin as a flag qubit, making this platform a promising candidate for scalable quantum repeaters.