  We theoretically investigate the dynamical nuclear spin polarization in a
quantum point contact (QPC) at finite magnetic field. We find that when the QPC
is tuned to be spin selective, at the conductance of e^2/h, a finite bias
induces a dipole-like (spatially anti-symmetric) nuclear polarization: at the
QPC center the polarization is zero, while, for GaAs parameters, the nuclear
spins down (up) are induced on the source (drain) side. We predict that the
dipole-like polarization pattern can be distinguished from a uniform
polarization due to a qualitatively different response of the QPC conductance
to the NMR field.
