  We demonstrate theoretically that it is possible to manipulate electron or
hole spins all optically in semiconducting carbon nanotubes. The scheme that we
propose is based on the spin-orbit interaction that was recently measured
experimentally; we show that this interaction, together with an external
magnetic field, can be used to achieve optical electron-spin state preparation
with a fidelity exceeding 99%. Our results also imply that it is possible to
implement coherent spin rotation and measurement using laser fields linearly
polarized along the nanotube axis, as well as to convert spin qubits into
time-bin photonic qubits. We expect that our findings will open up new avenues
for exploring spin physics in one-dimensional systems.
