  Systematic errors in spin rotation operations using simple RF pulses place
severe limitations on the usefulness of the pulsed magnetic resonance methods
in quantum computing applications. In particular, the fidelity of quantum logic
operations performed on electron spin qubits falls well below the threshold for
the application of quantum algorithms. Using three independent techniques, we
demonstrate the use of composite pulses to improve this fidelity by several
orders of magnitude. The observed high-fidelity operations are limited by pulse
phase errors, but nevertheless fall within the limits required for the
application of quantum error correction.
