Fast universal quantum gate above the fault-tolerance threshold in silicon

Fault-tolerant quantum computers that can solve hard problems rely on quantum error correction(1). One of the most promising error correction codes is the surface code(2), which requires universal gate fidelities exceeding an error correction threshold of 99 per cent(3). Among the many qubit platforms, only superconducting circuits(4), trapped ions(5) and nitrogen-vacancy centres in diamond(6) have delivered this requirement. Electron spin qubits in silicon(7-15) are particularly promising for a large-scale quantum computer owing to their nanofabrication capability, but the two-qubit gate fidelity has been limited to 98 per cent owing to the slow operation(16). Here we demonstrate a two-qubit gate fidelity of 99.5 per cent, along with single-qubit gate fidelities of 99.8 per cent, in silicon spin qubits by fast electrical control using a micromagnet-induced gradient field and a tunable two-qubit coupling. We identify the qubit rotation speed and coupling strength where we robustly achieve high-fidelity gates. We realize Deutsch-Jozsa and Grover search algorithms with high success rates using our universal gate set. Our results demonstrate universal gate fidelity beyond the fault-tolerance threshold and may enable scalable silicon quantum computers.

Automated summary

Fault-tolerant quantum computers rely on quantum error correction, and the surface code is one of the most promising error correction codes. However, only a few qubit platforms have met the required gate fidelities. In this study, the researchers demonstrate high-fidelity gate operations in silicon spin qubits using fast electrical control and a micromagnet-induced gradient field. The results show a two-qubit gate fidelity of 99.5% and single-qubit gate fidelities of 99.8%, surpassing the fault-tolerance threshold for universal gates.