  Here we explore spin dependent quantum transport through a single quantum dot
coupled to an optical microcavity. The spin current is generated by electron
tunneling between a single doped reservoir and the dot combined with intradot
spin flip transitions induced by a quantized cavity mode. In the limit of
strong Coulomb blockade, this model is analogous to the Jaynes-Cummings model
in quantum optics and generates a pure spin current in the absence of any
charge current. Earlier research has shown that in the classical limit where a
large number of such dots interact with the cavity field, the spin current
exhibits bistability as a function of the laser amplitude that drives the
cavity. We show that in the limit of a single quantum dot this bistability
continues to be present in the intracavity photon statistics. Signatures of the
bistable photon statistics manifest themselves in the frequency dependent shot
noise of the spin current despite the fact that the quantum mechanical average
spin current no longer exhibits bistability. Besides having significance for
future quantum dot based optoelectronic devices, our results shed light on the
relation between bistability, which is traditionally viewed as a classical
effect, and quantum mechanics.
