Quantum state reconstruction of classical and nonclassical light and a cryogenic opto-mechanical sensor for high-precision interferometry

Central topic of this thesis is the investigation of the quantum nature of light. This investigation is carried out in two separate experiments which are described in part I and part II respectively.In part I, classical and non-classical laser radiation is characterized at the quantum mechanical level with respect to its amplitude and phase uctuations, its photon number distribution and other observable quantities. This is done by employing recently developed methods of quantum state reconstruction. Such a complete characterization is of fundamental interest, since it can provide a much more detailed experimental description of light than previously known. Furthermore, since many experimental systems are analyzed by optical means, these methods may in future and important applications in the characterization of such systems in full quantum mechanical detail, by determining the state of the light held used as a probe before and after the interaction with the system.In part II, high precision position measurements via laser interferometry are investigated. Such measurements play an important role in the microscopic domain (optomechanical sensors, modern microscopy techniques) as well as in the macroscopic domain (development of large scale interferometers for the detection of gravitational waves). The goal of the second experiment is to explore the quantum mechanical limits in the precision with which the position of a macroscopic body can be determined.One common conceptual aspect of both experiments, besides the similar optical techniques employed, is that both attempt a high precision characterization of a harmonic oscillator system disturbed by stochastic noise. In part I, this oscillator is the light held, subject to quantum noise, in part II, it is a mechanical harmonic oscillator excited by thermal noise