Precision tomography of a three-qubit donor quantum processor in silicon

• Published in: arXiv.org 2022-01
• Main Authors: Mądzik, Mateusz T, Asaad, Serwan, Youssry, Akram, Joecker, Benjamin, Rudinger, Kenneth M, Nielsen, Erik, Young, Kevin C, Proctor, Timothy J, Baczewski, Andrew D, Laucht, Arne, Schmitt, Vivien, Hudson, Fay E, Itoh, Kohei M, Jakob, Alexander M, Johnson, Brett C, Jamieson, David N, Dzurak, Andrew S, Ferrie, Christopher, Blume-Kohout, Robin, Morello, Andrea
• Format: Article
• Language: English
• Subjects: Accuracy; Data processing; Electron spin; Electrons; Entangled states; Fault tolerance; Information processing; Microprocessors; Nanoelectronics; Nanotechnology devices; Nuclei (nuclear physics); Quantum computing; Quantum entanglement; Quantum phenomena; Qubits (quantum computing); Silicon; Tomography
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2106.03082

Nuclear spins were among the first physical platforms to be considered for quantum information processing, because of their exceptional quantum coherence and atomic-scale footprint. However, their full potential for quantum computing has not yet been realized, due to the lack of methods to link nuclear qubits within a scalable device combined with multi-qubit operations with sufficient fidelity to sustain fault-tolerant quantum computation. Here we demonstrate universal quantum logic operations using a pair of ion-implanted 31P donor nuclei in a silicon nanoelectronic device. A nuclear two-qubit controlled-Z gate is obtained by imparting a geometric phase to a shared electron spin, and used to prepare entangled Bell states with fidelities up to 94.2(2.7)%. The quantum operations are precisely characterised using gate set tomography (GST), yielding one-qubit average gate fidelities up to 99.95(2)%, two-qubit average gate fidelity of 99.37(11)% and two-qubit preparation/measurement fidelities of 98.95(4)%. These three metrics indicate that nuclear spins in silicon are approaching the performance demanded in fault-tolerant quantum processors. We then demonstrate entanglement between the two nuclei and the shared electron by producing a Greenberger-Horne-Zeilinger three-qubit state with 92.5(1.0)% fidelity. Since electron spin qubits in semiconductors can be further coupled to other electrons or physically shuttled across different locations, these results establish a viable route for scalable quantum information processing using donor nuclear and electron spins.