Quantum tomography of an entangled three-spin state in silicon

Abstract: Quantum entanglement is a fundamental property of coherent quantum states and an essential resource for quantum computing. While two-qubit entanglement has been demonstrated for spins in silicon, creation of multipartite entanglement, a first step toward implementing quantum error correction, has remained challenging due to the difficulties in controlling a multi-qubit array, such as device disorder, magnetic and electrical noises and exacting exchange controls. Here, we show operation of a fully functional three-qubit array in silicon and generation of a three-qubit Greenberger-Horne-Zeilinger (GHZ) state. We obtain a state fidelity of 88.0 percent by quantum state tomography, which witnesses a genuine GHZ-class quantum entanglement that is not biseparable. Our result shows the potential of silicon-based qubit platform for demonstrations of multiqubit quantum algorithms.