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 1 . 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 diamond 5 . 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. Among the candidates for large-scale quantum computing devices, silicon-based spin qubits offer an outstanding nanofabrication capability for scaling-up. In an array of three spin qubits in silicon, high-fidelity state preparation and control enable the creation of a three-qubit Greenberger–Horne–Zeilinger state with 88% state fidelity.