  High-fidelity control of quantum bits is paramount for the reliable execution
of quantum algorithms and for achieving fault-tolerance, the ability to correct
errors faster than they occur. The central requirement for fault-tolerance is
expressed in terms of an error threshold. Whereas the actual threshold depends
on many details, a common target is the ~1% error threshold of the well-known
surface code. Reaching two-qubit gate fidelities above 99% has been a
long-standing major goal for semiconductor spin qubits. These qubits are well
positioned for scaling as they can leverage advanced semiconductor technology.
Here we report a spin-based quantum processor in silicon with single- and
two-qubit gate fidelities all above 99.5%, extracted from gate set tomography.
The average single-qubit gate fidelities remain above 99% when including
crosstalk and idling errors on the neighboring qubit. Utilizing this
high-fidelity gate set, we execute the demanding task of calculating molecular
ground state energies using a variational quantum eigensolver algorithm. Now
that the 99% barrier for the two-qubit gate fidelity has been surpassed,
semiconductor qubits have gained credibility as a leading platform, not only
for scaling but also for high-fidelity control.
