Quantum behaviour in nano-mechanical systems

Abstract

The emerging field of nano-electro-mechanical systems (NEMS), in which the single mode of a nanomechanical oscillator plays the role of an active device, is receiving much attention due to its technological importance. The characteristic component that gives the name to these devices is an oscillator of nanometer size coupled to the electrons on the dot that transfer electrons one-by-one between a source and a drain lead. From a fundamental point of view, it is important to understand the interplay between the electronic transport and the nanomechanical motion of the oscillator quantum mechanically. This thesis contains the description and analysis of the dynamics of a nanomechanical oscillator coupled to a resonant tunnel junction (RTJ) and its realization as a shuttle device. The models we consider describe both the mechanical and electrical degrees of freedom quantum mechanically; Firstly, a RTJ coupled to a nanomechanical oscillator. Secondly, we report a first complete quantum mechanical analysis of a charge shuttle. We introduce a new non-perturbative quantum mechanical description for the strong interaction of both the electrical and the mechanical object, which is beyond the existing experiments. We describe a nonequilibrium Green’s function formalism: a well suited technique to treat this kind of far from equilibrium systems, which can deal with very small to very large applied bias. The numerical implementation of these models are discussed in detail, and the transient and the steady state behavior of the system is also considered here for the quantum dynamics of the oscillator as a function of time. This will provide useful insight for the design of experiments aimed at studying the quantum behavior of an oscillator.