Analysis of frequency-dependent spin current shot noise of a single quantum dot coupled to an optical microcavity

摘要

The discrete nature of charge carriers in electrical devices along with the probabilistic nature of quantum mechanics give rise to quantum shot noise, which is an intrinsic source of current noise present in all electrical circuits based on either charge or spin transport. The frequency spectrum of the shot noise gives additional information about processes in the device that cannot be obtained from the conductance including the interactions of carriers, their kinetics, entanglement, etc. Because of this, the study of shot noise in nanostructures has developed into an active field of mesoscopic physics. Here we examine spin current and shot noise generated by a single quantum dot coupled to an optical microcavity. The dot is connected to normal leads at zero bias voltage with a single energy level close to the Fermi energy. In the absence of any charge current, a pure 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. Our novel approach is based on the Born-Markov master equations to describe both the quantized bosonic field and the transport through the dots combined with the quantum regression theorem to calculate the shot noise. 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. In the limit of a single quantum dot we show that this bistability continues to be present in the cavity field Q-distribution and 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.