We report the experimental realization and tomographic analysis of quantum light states obtained by exciting a classical thermal field by a single photon. Such states, although completely incoherent, possess a tunable degree of quantumness which is here exploited to put to a stringent experimental test some of the criteria proposed for the proof and the measurement of state nonclassicality. The quantum character of the states is also given in quantum information terms by evaluating the amount of entanglement that they can produce.
There is a common understanding in quantum optics that nonclassical states of light are states that do not have a positive semidefinite and sufficiently regular Glauber-Sudarshan
P function. Almost all known nonclassical states have
P functions that are highly irregular, which makes working with them difficult and direct experimental reconstruction impossible. Here we introduce classes of nonclassical states with regular, non-positive-definite
P functions. They are constructed by ``puncturing'' regular smooth positive
P functions with negative Dirac-$\ensuremath{\delta}$ peaks or other sufficiently narrow smooth negative functions. We determine the parameter ranges for which such punctures are possible without losing the positivity of the state, the regimes yielding antibunching of light, and the expressions of the Wigner functions for all investigated punctured states. Finally, we propose some possible experimental realizations of such states.
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.