Quantum bistability and spin current shot noise of a single quantum dot coupled to an optical microcavity

Here we explore the quantum-mechanical limit of bistability that appears in the spin-dependent 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. Earlier research has shown that in the classical limit where a large number of such dots interacts with the cavity so that quantum effects were ignorable, the average spin current exhibits bistability as a function of the laser 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.