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.
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.
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−-center) and the non-interacting nuclear spins. From this we lay out conditions for realizing a scalable nuclear-spin (13C or 29Si) register, wherein independent control of the qubits alongside their mutual controlled operations using the central electron spin associated to the 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.
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(13Cor29Si)and silicon vacancy color centers(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.
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 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% and a three-qubit Greenberger-Horne-Zeilinger (GHZ)-type state with a fidelity of 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%, extending the entanglement lifetime by a factor of 240. We further confirm the generality of this approach in an additional heterogeneous 29Si-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.
Quantum networks based on solid-state spin defects present a transformative approach to secure communication and distributed quantum computing, utilizing quantum entanglement and coherent spin–photon interfaces. Silicon carbide (SiC) stands out as a compelling material platform due to its unique combination of a wide bandgap, high optical nonlinearity, CMOS-compatible fabrication, and controllable spin-active defects. These intrinsic properties facilitate efficient photon emission, robust spin coherence at both room and cryogenic temperatures, and integration with photonic nanostructures. Recent advancements in defect engineering and micro-nanophotonics have unlocked the potential of SiC quantum nodes, which feature electron-nuclear spin systems for high-fidelity quantum operations and long-lived quantum memories. Key steps such as single-shot readout and spin-photon entanglement have been successfully demonstrated, bringing SiC closer to a real quantum network platform. This review offers a comprehensive overview of the advancements in SiC-based quantum networks, encompassing key aspects such as defect fabrication methodologies, optimization of spin-photon interfaces, and strategies for photonic integration. Additionally, it examines the existing challenges and outlines promising future directions in this rapidly evolving field.
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.
Quantum networks will enable the transmission of quantum information over long distances, allowing us to link quantum computers for applications such as quantum cryptography, astronomical interferometry, and blind quantum computing. The silicon-vacancy center in diamond has emerged as a promising scalable solid-state platform capable of efficiently interfacing its electron spin with photons for long-range communication. This thesis investigates two long-lived nuclear spin qubits as quantum memories to significantly expand the quantum state storage and processing capabilities of this networking node. First, we demonstrate that selective isotope implantation gives a deterministic 29Si high-fidelity nuclear memory with coherence times over two seconds, enabling its integration into a two-node quantum network through 35 km of optical fiber deployed through the Boston metropolitan area. Next, we explore the control of a nearby 13C nuclear spin robust against repeated readouts and resets of the electron networking qubit, and utilize it to show a quadratic rate enhancement for entanglement swapping between two incoming photonic qubits. Together, these results advance our three-qubit node toward realistic operation as a quantum repeater to boost entanglement rates in a long-range network.