"Cavity optomechanics is a flourishing research field concerned with the study of macroscopic objects in a regime where quantum mechanical effects become apparent. A strong interaction between the optical field and the mechanical motion of optomechanical resonators, usually mediated by radiation pressure, enables both new photonic technologies as well as fundamental experiments that are at the heart of quantum mechanics.This proposal aims to study micro- and nano-optomechanical systems cooled close to their ground state of motion to advance both fundamental and applied concepts in quantum optomechanics.A first aim is to study a recently developed optomechanical device based on a 2D photonic crystal defect cavity. In particular, we aim to cool this device down to its ground state of motion by embedding it in a Helium-3 cryostat and using radiation pressure induced laser cooling to reach its ground state of motion. The high optomechanical coupling strength measured on these devices promises to allow ground state cooling with moderate efforts.A second objective is to implement the technique of motional side-band spectroscopy, adapted from ion trapping experiments, to characterize the degree of occupancy of the ground state of motion of optomechanical resonators, providing a definite quantum-mechanical signature in these macroscopic objects.Finally, we will use the recently observed effect of optomechanically-induced transparency (OMIT) in microresonators, in which the optomechanical coupling induces a very narrow transparency window accompanied by a strong group velocity reduction, for storing and stopping light pulses in optomechanical modes.This proposal will allow the applicant, a physicist recently graduated with distinction from the Institute of Photonic Sciences (ICFO) in Barcelona, to join the Laboratory of Photonics and Quantum Measurements in the Federal Institute of Technology in Lausanne (EPFL), a group with high recognition in this field of research."