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

Area of Science:

• Quantum computing and information processing.
• Solid-state quantum systems.
• Nuclear spin physics.

Background:

• Nuclear spins offer exceptional quantum coherence and an atomic-scale footprint for quantum information processing.
• Realizing the full potential of nuclear qubits for quantum computing is hindered by the lack of scalable linking methods and high-fidelity multi-qubit operations.

Purpose of the Study:

• To demonstrate universal quantum logic operations on nuclear spins within a silicon nanoelectronic device.
• To achieve high-fidelity entanglement between nuclear qubits and a shared electron spin.
• To establish a viable pathway for scalable quantum information processing using donor spins in silicon.

Main Methods:

• Utilized ion-implanted 31P donor nuclei in a silicon nanoelectronic device.
• Implemented a nuclear two-qubit controlled-Z gate via geometric phase imparted to a shared electron spin.
• Employed gate set tomography (GST) for precise characterization of quantum operations.

Main Results:

• Achieved fidelities up to 94.2(2.7)% for entangled Bell states between nuclear qubits.
• Obtained high average gate fidelities: up to 99.95(2)% for one-qubit and 99.37(11)% for two-qubit operations.
• Demonstrated a three-qubit Greenberger-Horne-Zeilinger state with 92.5(1.0)% fidelity, showing entanglement between two nuclei and a shared electron.

Conclusions:

• Nuclear spins in silicon are nearing the performance required for fault-tolerant quantum processors.
• The demonstrated high-fidelity operations and entanglement establish a viable route for scalable quantum information processing.
• Coupling electron spin qubits to other electrons or physically shuttling them further enhances the scalability of this approach.