  We examine the spin current generated by quantum dots embedded in an optical
microcavity. The dots are connected to leads, which allow electrons to tunnel
into and out of the dot. The spin current is generated by spin flip transitions
induced by a quantized electromagnetic field inside the cavity with one of the
Zeeman states lying below the Fermi level of the leads and the other above. In
the limit of strong Coulomb blockade, this model is analogous to the
Jaynes-Cummings model in quantum optics. We find that the cavity field
amplitude and the spin current exhibit bistability as a function of the laser
amplitude, which is driving the cavity mode. Even in the limit of a single dot,
the spin current and the Q distribution of the cavity field have a bimodal
structure.
