Quantum Phenomena In Light-atom Interactions

The field of atom-light interaction is a major topic in quantum optics,and has drawn widespread attention.Multi-wave mixing,electromagnetically induced transparency?EIT?and Autler–Townes?AT?splitting are some of the most important quantum coherence phenomena in the field.This thesis studies certain significant physical issues of the above-mentioned phenomena from both theoretical and experimental aspects,and describes the building of a device which can produce a cold atomic sample of ultrahigh optical density and a two-dimensional optical lattice setup for Bose–Einstein condensation?BEC?.The principal results are summarized as follows.First,an Autler–Townes spectroscopy scheme based on phase conjugate six-wave mixing?SWM?is proposed to detect the AT doublet of high-lying states in a Doppler broadened cascade four-level system.The effect of Doppler broadening on the SWM spectrum is discussed from a time-domain viewpoint.Second,the asymmetry of the EIT absorption curve induced by a resonant coupling field in a?-type three-level system for ⁸⁷Rb cold atoms was investigated.It was found that this phenomenon is induced by the other excited state,which is separated by an interval of 814 MHz.In an experiment conducted with cold atoms in a magneto-optical trap,the experimental results agreed well with the theoretical prediction.Third,a cold atom sample with an ultrahigh optical density as high as 3000 was prepared using a single beam optical dipole trap.This system can be an ideal experimental system for quantum optics and nonlinear optics because of its high atomic density,easy access,and stability.A four-wave mixing experiment was also performed in this system,wherein it was observed that the intensity of the Stokes or anti-Stokes light showed obvious threshold features depending on the experimental conditions.This could be a laser without inversion effect.Fourth,based on our hybrid BEC trap,a two-dimensional optical lattice setup was successfully built,with which a wealth of experience was accumulated for future experiments on a three-dimensional optical lattice and the follow-up quantum simulation.Fifth,when the waveguide into a ⁸⁷Rb atom BEC was irradiated by a blue-detuned laser beam,it was observed that the center of the atomic cloud did not expand.From analysis of the experimental results,it can be deduced that this is an Anderson localization phenomenon caused by the disordered speckle field which is formed when the light field passes through the‘dirty'vacuum chamber wall.