Thesis (M.S.)--Brigham Young University. Dept. of Physics and Astronomy, 2005. / Includes bibliographical references (leaves 20-24).

No description available.

The work of this dissertation has been to prove that the coherence of multiphoton excitation can be studied by an appropriately phased and time delayed sequence of pulses. An application of this fundamental study of coherence has been made for the enhancement of third harmonic generation. The coherent recovery of the energy lost to the two photon absorption process enalled a larger propagation distance for the fundamental than in an interaction which is incoherent or coherent, but not using a 90 degree phase shifted pulse pair. Phase matching over this longer propagation distance gave an enhancement of third harmonic generation.

A pair of nonidentical two-level atoms, separated by a fixed distance R, interact through photon exchange. The system is described by a state vector which is assumed to be a superposition of four "essential states": (1) the first atom is excited, the second one is in the ground state, and no photon is present, (2) the first atom is in its ground state, the second one is excited, and no photon is present, (3) both atoms are in their ground states and a photon is present, and (4) both atoms are excited and a photon is also present. The system is initially in state (1). The probabilities of each atom being excited are calculated for both the minimally-coupled interaction and the multipolar interaction in the electric dipole approximation. For the minimally-coupled interaction Hamiltonian, the second atom has a probability of being instantaneously excited, so the interaction is not retarded. For the multipolar interaction Hamiltonian, the second atom is not excited before the retardation time, which agrees with special relativity. For the minimally-coupled interaction the nonphysical result occurs because the unperturbed Hamiltonian is not the energy operator in the Coulomb gauge. For the multipolar Hamiltonian in the electric dipole approximation the unperturbed Hamiltonian is the energy operator. An active view of unitary transformations in nonrelativistic quantum electrodynamics is used to derive transformation laws for the potentials of the electromagnetic field and the static Coulomb potential. For a specific choice of unitary transformation the transformation laws for the potentials are used in the minimally-coupled second-quantized Hamiltonian to obtain the multipolar Hamiltonian, which is expressed in terms of the quantized electric and magnetic fields.

No description available.

Le contrôle des états quantiques de la lumière est une étape nécessaire pour la transmission et le traitement quantiques des informations. Un nuage d'atomes froids constitue un milieu optiquement non-linéaire très intéressant pour créer et manipuler des états photoniques. Le sujet de cette thèse est l'étude expérimentale de telles non-linéarités, induites entre des photons optiques par leur couplage avec des atomes de Rydberg. Les états de Rydberg sont des états atomiques très excités (n>30), qui permettent de créer des interactions photon-photon par l'intermédiaire de leurs interactions dipôle-dipôle à longue distance (>10µm). Nous utilisons une cavité de faible finesse pour transformer ces interactions en effets observables sur un faisceau de très faible intensité, ce qui peut permettre de produire des états non-classiques de lumière. / The control of quantum states of light is a necessary step for quantum information transportation and processing. Cold atomic memories are one of the prime candidates for storing and manipulating photonic states. This thesis is a study of optical non-linear effects created using Rydberg states. Rydberg states are highly excited states (n>30) of atoms, which are useful in realizing photon-photon interactions because of their long distance (>10µm) dipole-dipole interactions. We utilize a low finesse cavity to transform phase shifts into intensity correlations which would allow one to generate arbitrary non-classical states of light

No description available.

No description available.