Coherent properties of nanoelectromechanical systems

We study the properties of a nanoelectromechanical system in the coherent regime, where the electronic and vibrational time scales are of the same order. By employing a master-equation approach, we obtain the stationary reduced density matrix retaining the coherences between vibrational states. Depending on the system parameters, two regimes are identified, characterized by either (i) an effective thermal state with a temperature lower than that of the environment or (ii) strong coherent effects. A marked cooling of the vibrational degree of freedom is observed with a suppression of the vibron Fano factor down to sub-Poissonian values and a reduction of the position and momentum quadratures.