Quantum optical interferometry

This dissertation details a series of experiments conducted at the few-photon level involving quantum entanglement and quantum interferometry. The dissertation begins with the presentation of the quantum optical realization of a thought experiment proposed by Lucien Hardy that demonstrates a striking contrast between the predictions of quantum mechanics and those of local realistic theories. The experiment uses only pairs of particles in a non-maximally entangled state to produce a nonstatistical contradiction between the quantum mechanical and local realistic predictions, thereby surpassing Bell and GHZ-type inequality tests. This is followed by a description of the process of parametric down-conversion along with the demonstration of two separate experimental techniques that use quantum interference to improve the quality of polarization entanglement in photon pairs. The work with photon pairs is extended to several experiments involving multiple pairs of photons. These experiments include a scheme to prepare heralded, path-entangled states from a down-conversion source, as well as demonstrations of both symmetric and antisymmetric behavior by composite states of photons. The theory of multiple pair production is presented to explain the quality of interference in these experiments. Finally, novel multiphoton detectors are employed to demonstrate phase measurement sensitivity at the standard-quantum limit with a coherent state interferometer. For the first time phase-independent sensitivity is achieved through the use of a Bayesian statistical analysis of the photodetector data. The result of phase-independent sensitivity is also demonstrated in an experiment using ordinary photodiode detectors.