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.