Noise and Bistabilities in Quantum Shuttles

We present a study of current fluctuations in two models proposed as quantum shuttles. Based on a numerical evaluation of the first three cumulants of the full counting statistics we have recently shown that a giant enhancement of the zero-frequency current noise in a single-dot quantum shuttle can be explained in terms of a bistable switching between two current channels. By applying the same method to a quantum shuttle consisting of a vibrating quantum dot array, we show that the same mechanism is responsible for a giant enhancement of the noise in this model, although arising from very different physics. The interpretation is further supported by a numerical evaluation of the finite-frequency noise. For both models we give numerical results for the effective switching rates.