  Zeeman splitting of 1D hole subbands is investigated in quantum point
contacts (QPCs) fabricated on a (311) oriented GaAs-AlGaAs heterostructure.
Transport measurements can determine the magnitude of the g-factor, but cannot
usually determine the sign. Here we use a combination of tilted fields and a
unique off-diagonal element in the hole g-tensor to directly detect the sign of
g*. We are able to tune not only the magnitude, but also the sign of the
g-factor by electrical means, which is of interest for spintronics
applications. Furthermore, we show theoretically that the resulting behavior of
g* can be explained by the momentum dependence of the spin-orbit interaction.
