Abstract
This thesis reports our studies on the phenomenon of electromagnetically induced transparency (EIT) and its applications including slow light effect, low-light-level photon switching, light storage and retrieval, manipulations of optical properties of stored light pulses, and a new cross-phase modulation (XPM) scheme based on light-storage technique. EIT is the phenomenon that the absorption of a weak probe field is greatly reduced or even completely inhibited by the presence of a strong coupling field. We study the EIT effect in laser-cooled 87Rb atoms by measuring the EIT spectra. The experimental data are in agreement with the theoretical predictions. We also study the slow light effect with EIT. In our experiment, the group velocity of a light pulse can be greatly slowed down to around 1500 m/s or vg/c ~ 5×10-6 with the steep dispersion of EIT media. Photon switching system is an important application of slow light effect. We experimentally study the transient behaviors of photon switching and provide theoretical explanations to these behaviors. We also experimentally demonstrate a single-photons-density switching. The results show that the single-photons switching is feasible and may has potential applications in quantum communication and computation. The phenomenon of light storage and retrieval with dynamical EIT effect is based on the coherence transfer between light and collective atomic spin coherence, which can be used a quantum memory. We observe the light storage and retrieval in cold 87Rb atoms and propose a simple method of beat-note interferometer to directly demonstrate the process of light storage and retrieval is phase coherent. We also experimentally manipulate the width, frequency and polarization of retrieved light by controlling the retrieval process of light storage. We experimentally demonstrate a new XPM scheme based on the light-storage technique. The proposed scheme can work in pulse regime and has the same figure of merit compared to the one using the static EIT under the constant coupling field. Nevertheless, the phase shift and the energy loss of a probe pulse induced by a signal pulse are neither influenced by the coupling intensity nor by the atomic optical density in the light-storage XPM scheme. This scheme enhances the flexibility of the experiment and makes possible of a single-photons π phase gate.