Silicon Carbide Quantum Node Combines Processing Power with Robust Data Storage

Scientists are actively pursuing solid-state color centres as building blocks for future quantum networks, but creating scalable nodes capable of both processing and storing quantum information with high accuracy presents a significant hurdle. Shuo Ren, Rui-Jian Liang, and Zhen-Xuan He, along with Ji-Yang Zhou et al. from the Laboratory of Quantum Information at the University of Science and Technology of China, have now demonstrated a fully functional quantum node within silicon carbide, utilising electrons as processors and nuclei as memory. Their research details a novel pulse sequence combining dynamical decoupling and hyperfine interactions to achieve decoherence-protected universal gate operations, deterministically generating entangled states with a fidelity of 90%, surpassing thresholds required for certain quantum network architectures and representing a crucial step towards practical, scalable quantum technologies.

This innovative node integrates electron spins as quantum processors and nearby nuclear spins as quantum memory, achieving a crucial combination previously lacking in solid-state systems.

Researchers designed a novel pulse sequence, termed dynamical decoupling with radiofrequency control (DDRF), to orchestrate high-fidelity universal gate operations between the processor and memory qubits. This technique effectively shields quantum information from environmental noise, preserving coherence and enabling robust quantum computation.
Specifically, the work demonstrates the deterministic preparation of entangled states within the SiC quantum node with a fidelity of 90 ±3%. This performance surpasses the fault-tolerance threshold required by certain quantum network architectures, paving the way for more reliable quantum communication and computation.

The achievement relies on a shallow PL6 color center, created through ion implantation, coupled with a strongly interacting silicon nuclear spin. By combining dynamical decoupling with precise radiofrequency control of the nuclear spin, the team realised universal gate operations and enhanced the functionality of the quantum node.

This breakthrough addresses a key challenge in quantum technology: building fully functional nodes capable of both processing and storing quantum information. Current demonstrations often focus on single functions, limiting the versatility and scalability of quantum networks. The SiC platform offers advantages such as long spin coherence times, compatibility with telecommunication wavelengths, and mature microfabrication technologies.

The demonstrated DDRF technique not only enables high-fidelity gates but also extends the applicability of decoherence-protected control to shallow defects, crucial for integration with nanophotonic devices and waveguides. These results establish a clear pathway towards constructing scalable and fully functional quantum nodes based on silicon carbide, accelerating the development of advanced quantum technologies.

Electron-nuclear quantum state preparation and room-temperature Bell state characterisation represent significant advances in quantum information science

A 72-qubit superconducting processor forms the foundation of this work, utilized to demonstrate a fully functional quantum node in silicon carbide where electrons act as quantum processors and nuclear spins serve as quantum memory. Initialisation of the system commenced with the application of a microwave (MW1) π/2 pulse, preparing the state 1/√2(|0, ↑⟩ + |−1, ↑⟩).

Subsequently, a radiofrequency (RF) π-pulse conditionally flipped the nuclear spin, yielding the state 1/√2(|0, ↑⟩ + |−1, ↓⟩). Quantum state tomography, performed at room temperature without cryogenic cooling, then characterised the resulting Bell state. Statistical uncertainties within the reconstructed density matrices, and the derived fidelity values, were estimated using a Monte Carlo method accounting for Poissonian photon-counting noise during tomographic measurements.

The total preparation time was set to 14.7μs, exceeding the electron spin coherence time, and the real and imaginary parts of the density matrix were recorded to assess the prepared Bell state. Measurements indicated a fidelity reaching approximately 0.70 ±0.03. To achieve decoherence-protected gate operations, a composite pulse sequence combining dynamic decoupling (DD) microwave pulses and radiofrequency (RF) pulses was implemented.

The RF frequency was tuned to the nuclear spin transition corresponding to the electron spin state |−1⟩, and RF pulses were inserted into each idle time τ of the DD sequence, forming the pattern (τ −π −2τ −π −τ)N. This sequence enabled the realisation of two fundamental gate operations between the processor and memory, selectively controlling a single nuclear spin based on the electron spin state. Nuclear Rabi oscillations and Ramsey fringes were observed and fitted with Lorentzian functions to calibrate the nuclear gate operations.

High-fidelity entanglement via dynamical decoupling and radiofrequency control of silicon carbide spins enables advanced quantum sensing and computation

A fidelity of 90±3% was achieved in the deterministic preparation of entangled states within a silicon carbide quantum node. This result demonstrates a fully functional quantum node where electron spins act as processors and nuclear spins serve as quantum memory. The research details a composite pulse sequence, termed dynamical decoupling with radiofrequency control, enabling universal gate operations between the processor and memory qubits while preserving coherence.

Specifically, this sequence combines dynamical decoupling techniques with precise radiofrequency manipulation of the nuclear spin. Electron spin transitions are driven by microwave pulses, designated MW1 and MW2, which conserve nuclear spin. A radiofrequency pulse then drives an electron spin-conserving transition of the nuclear spin.

This approach leverages a strong hyperfine coupling of 12.4MHz between the electron spin of the PL6 defect and a nearby silicon-29 nuclear spin. Optically detected magnetic resonance spectra recorded at zero magnetic field and under a 4.2 Gauss field aligned with the PL6 symmetry axis confirmed this coupling.

The work establishes a pathway towards scalable quantum nodes based on silicon carbide, exceeding the fault-tolerance threshold required by certain quantum network architectures. By systematically demonstrating strong-coupling-enabled, universal electron, nuclear control, the study addresses a significant challenge in solid-state quantum technologies.

This control is particularly crucial for shallow, ion-implanted defects in SiC, facilitating integration with nanophotonic cavities and waveguides for advanced quantum networking. The achieved fidelity represents a substantial step towards realizing practical and versatile quantum nodes for distributed quantum computing and long-distance quantum communication.

High fidelity entanglement and universal gate operations in a silicon carbide quantum node represent a significant step towards scalable quantum computing

Scientists have demonstrated a fully functional quantum node within a silicon carbide material, integrating electron spins as processors and nuclear spins as memory. This hybrid system utilizes specifically designed pulse sequences combining dynamical decoupling and hyperfine interactions to achieve universal gate operations between the processor and memory components.

Deterministic preparation of entangled states was achieved with a fidelity of 90 percent, exceeding the fault-tolerance threshold necessary for certain quantum network architectures. The achievement of high-fidelity entanglement represents a significant step towards scalable quantum computing and networking.

This work successfully implements decoherence-protected universal gate operations, a critical capability previously elusive in silicon carbide systems. By leveraging the established semiconductor processing technologies of silicon carbide, this approach offers a potentially scalable and technologically viable pathway for robust quantum information processing.

Although current gate performance is limited by high-frequency noise, the authors suggest that isotopic engineering of the silicon carbide host crystal could suppress the nuclear spin bath, extend coherence times, and further improve gate fidelity. Future research will likely focus on implementing optical interfaces to connect these quantum nodes, paving the way for near-term quantum network applications.