Nonlinearities and quantum phenomena in nanoelectromechanical systems

This dissertation addresses different types of nonlinear phenomena in nanoelectromechanical systems (NEMS) with an aim to find quantum behavior in them. Quantum mechanics is a theory that describes physics at the atomic scale. Without it many phenomena such as the electronic properties of crystalline matter would not be properly understood. However, the way the world works on quantum scale is nothing like how it appears in the classical perception of human beings. Although all the objects around us are made of atoms, none of the objects show quantum behavior since perturbations coming from their surroundings destroy the quantum states. During the last decade, NEMS have caught the interest of the scientific community since they are promising candidates to study and test quantum mechanics in the macroscopic scale. In recent experiments, optomechanical systems have been used to cool nanomechanical resonators to their ground state. Ground state cooling is a requirement for the observation of the quantum nature of the mechanical resonator. But in addition to being close to the ground state, nonlinearities are needed to distinguish the quantum behavior from the classical one. Therefore, great effort is spent studying nonlinearities either within the mechanical resonator or due to an external system coupled to the nanomechanical resonator. This dissertation is composed of an introduction and four research articles published in high-level physics journals. The introduction starts by discussing the basic theory of NEMS. Then it specifies some relevant nonlinearities that occur in nanoelectromechanical systems, and how one can use them for the observation of quantum phenomena on macroscopic scale. The details of such nonlinearities are described in the research articles presented in the thesis.