  Semiconductor spin qubits based on spin-orbit states are responsive to
electric field excitation allowing for practical, fast and potentially scalable
qubit control. Spin-electric susceptibility, however, renders these qubits
generally vulnerable to electrical noise, which limits their coherence time.
Here we report on a spin-orbit qubit consisting of a single hole
electrostatically confined in a natural silicon metal-oxide-semiconductor
device. By varying the magnetic field orientation, we reveal the existence of
operation sweet spots where the impact of charge noise is minimized while
preserving an efficient electric-dipole spin control. We correspondingly
observe an extension of the Hahn-echo coherence time up to 88 $\mu$s, exceeding
by an order of magnitude the best reported values for hole-spin qubits, and
approaching the state-of-the-art for electron spin qubits with synthetic
spin-orbit coupling in isotopically-purified silicon. This finding largely
enhances the prospects of silicon-based hole spin qubits for scalable quantum
information processing.
