  We study an electrically controlled quantum spin Hall antidot embedded in a
two-dimensional topological insulating bar. Helical edge states around the
antidot and along the edges of the bar are tunnel coupled. The close connection
between spin and chirality, typical of helical systems, allows to generate a
spin-polarized current flowing across the bar. This current is studied as a
function of the external voltages, by varying the asymmetry between the
barriers. For asymmetric setups, a switching behavior of the spin current is
observed as the bias is increased, both in the absence and in the presence of
electron interactions. This device allows to generate and control the
spin-polarized current by simple electrical means.
