  We experimentally demonstrate a method for obtaining nuclear spin
hyperpolarization, that is, polarization significantly in excess of that
expected for a thermal equilibrium. By exploiting a modified Overhauser
process, we obtain more than 68% nuclear anti-polarization of phosphorus donors
in silicon. This polarization is reached with a time constant of ~150 seconds,
at a temperature of 1.37 K and a magnetic field of 8.5 T. The ability to obtain
such large polarizations is discussed with regards to its significance for
quantum information processing and magnetic resonance imaging.
