Quantum Electro-mechanical Systems (QEMS)

We give a quantum description of a Quantum Electro-Mechanical System(QEMS) comprising a single quantum dot harmonically bound between two electrodes and facilitating a tunnelling current between them. An example of such a system is a fullerene molecule between two metal electrodes. The description is based on a quantum master equation for the density operator of the electronic and vibrational degrees of freedom and thus incorporates the dynamics of both diagonal (population) and off diagonal (coherence) terms. We derive coupled equations of motion for the electron occupation number of the dot and the vibrational degrees of freedom, including damping of the vibration and thermo-mechanical noise, and give a semiclassical description of the dynamics under a variety of bias conditions. This dynamical description is related to observable features of the system including the stationary conductance as a function of bias voltage