  We present a technique for manipulating the nuclear spins and the emission
polarization from a single optically active quantum dot. When the quantum dot
is tunnel coupled to a Fermi sea, we have discovered a natural cycle in which
an electron spin is repeatedly created with resonant optical excitation. The
spontaneous emission polarization and the nuclear spin polarization exhibit a
bistability. For a sigma(+) pump, the emission switches from sigma(+) to
sigma(-) at a particular detuning of the laser. Simultaneously, the nuclear
spin polarization switches from positive to negative. Away from the
bistability, the nuclear spin polarization can be changed continuously from
negative to positive, allowing precise control via the laser wavelength.
