Stryzhenko S. Researching and numerical modelling sources of light with quantum properties based on multi-level atoms

The thesis presents results of experimental, theoretical, and numerical research of several quantum light sources based on multi-level atoms. Firstly, we experimentally implemented and numerically simulated a source of biphotons based on resonant four-wave mixing. The source utilizes four levels of rubidium-87, including two hyperfine levels of the ground state and two excited levels of the fine structure. The numerical simulation, based on the equations describing the interaction between laser light and matter in a one-dimensional medium of high optical depth and high birefringence, employs the density matrix formalism and rotating wave and Weißkopf-Wigner approximations. This approach accurately reproduces interaction between multi-level atoms and light, considering degeneracy by the magnetic quantum number. To enable realistic time simulations on conventional personal computers, the simulation was optimized using the half-vectorization method. Despite utilizing semiclassical approximation, the simulation allowed to determine polarization of the one-photon field generated by the source of biphotons. Secondly, the proposed simulation was also used to numerically model Raman superfluorescence in a three-level scheme within a spatially inhomogeneous medium. The simulation results were utilized to design an experimental setup for researching Raman superfluorescence in hollow waveguides filled with laser-cooled atoms of rubidium-87. The obtained results aligned both qualitatively and quantitatively with experimental data. Following the experiments and numerical simulations, a simple theoretical model of superfluorescence in inhomogeneous media was proposed. This model relies on the concept of maximal number of atoms collectively participating in the initial superfluorescent burst, providing an explanation for all observed properties of the phenomenon. Finally, the thesis delves into the theoretical exploration of a single-photon source consisting of a single three-level atom coupled to a single-mode cavity, where one mirror is semi-transparent. A theory describing the interaction between this source and a semi-infinite one-dimensional bath was developed. This theory demonstrated that, under specific regime of interaction where quantum state of the cavity is unpopulated, the source can produce a photon of desired shape on demand.