Quantum tomography of an entangled three-qubit state in silicon

Quantum entanglement is a fundamental property of coherent quantum states and an essential resource for quantum computing'. In large-scale quantum systems, the error accumulation requires concepts for quantum error correction. A first step toward error correction is the creation of genuinely multipartite entanglement, which has served as a performance benchmark for quantum computing platforms such as superconducting circuits(2,3), trapped ions(4) and nitrogen-vacancy centres in diamonds. Among the candidates for large-scale quantum computing devices, silicon-based spin qubits offer an outstanding nanofabrication capability for scaling-up. Recent studies demonstrated improved coherence times(6-8), high-fidelity all-electrical control(9-13), high-temperature operation(14,15) and quantum entanglement of two spin qubits(9,11,12). Here we generated a three-qubit Greenberger-Horne-Zeilinger state using a low-disorder, fully controllable array of three spin qubits in silicon. We performed quantum state tomography(16) and obtained a state fidelity of 88.0%. The measurements witness a genuine Greenberger-Horne-Zeilinger class quantum entanglement that cannot be separated into any biseparable state. Our results showcase the potential of silicon-based spin qubit platforms for multiqubit quantum algorithms.

Automated summary

Silicon-based spin qubits offer outstanding nanofabrication capability and have demonstrated improved coherence times, high-fidelity all-electrical control, high-temperature operation, and quantum entanglement of two spin qubits. These results showcase the potential of silicon-based spin qubit platforms for multiqubit quantum algorithms.