The Experimental Research On Three-wave Mixing Based On Atomic Raman Scattering

As the nonlinear media, Alkali atomic ensemble has been widely applied in quantum information process and quantum manipulation because of the memory capability and collective enhancement. Raman scattering process based on Alkali atomic ensemble has become an important method to facilitate quantum state exchange between light and matter. In this thesis, we investigate the three-wave mixing of Raman process based on Alkali (Rb87) atomic ensemble.The threshold is an important feature of Raman process but without detail study in the past research. In the hot Rb87atomic ensemble, the low threshold level for Raman pump field has been observed and is lack of reasonable explanation. At the same time, above threshold or in high gain region, the application of phase correlation between atomic spin wave and scattering field is limited by the random phase of scattering field. Furthermore, the noise generated spontaneously in atomic ensemble will disturb the quantum effect in Raman process. Base on above discussion, our detail research project is listed as follow:1. We use a simple theory of three-wave mixing to explain the low-threshold effect of Raman process based on a hot Rb87atomic ensemble. And in the experiment, we find the threshold level for the Raman pump field depends on the decoherence time of the atomic spin wave and the coupling coefficient between light and the atomic ensemble. Our research results demonstrate that the atomic Raman oscillation is a mirrorless parametric oscillation process, and its onset is the coherent buildup of atomic spin wave. The detail research is shown in the second chapter.2. We utilize the memory ability of atomic spin wave and intensity correlation measurement to eliminate the effect of spontaneous random phase of scattering field from Raman process. A new scheme for controlled storage and retrieval of the optical phase information based on Raman process in atomic ensemble is proposed and has been demonstrated experimentally. Based on the scheme, an interference pattern of the intensity correlation function between the scattering fields from write-in and read-out processes has been observed as the stored phase is scanned. This research work is introduced in the third chapter.3. In the fourth chapter, we investigate the four-wave mixing (FWM) noise during the Raman read process in a hot Rb87atomic ensemble. It is demonstrated experimentally that the FWM noise can be greatly suppressed by simply reducing the FWM transition channels with a circularly polarized read beam based on the atomic Transition Selection Rule. At the same time the retrieval efficiency remains relatively high.