Quantum Control Of Cavity Electromagnetically Induced Transparency System’s Spectral Characteristics

The technology of electromagnetically induced transparency (EIT) and Cavity QED are two unique quantum control means and have special ability in manipulation and control the interaction between light and matters. For EIT, the main character is that medium for detect-ing light absorption decrease significantly and the dispersion significantly enhanced via a strong coupling optical filed. Cavity QED is mainly used to study the quantum behaviors be-tween light field and atoms in limited space. It can be used as effective platform to manipulate single photon or a quantum amplifier. The combination of this two technology will produce many novel optical phenomenon.1. We propose a scheme for realizing a quantum nondemolition (QND) measurement of a small number of optical photons. Our scheme has two stages. First, we couple a propagating light pulse with fixed photon number to a trapped cold atomic gas within a cavity, such that the pulse is stored within a collective polariton mode. Second, a small photon number meas-urement is engineered by monitoring the cavity transmission spectrum. Since the polariton mode profile is preserved during the process of detecting spectrum, photon-number QND measurement could be achieved by retrieving the light pulse from the polariton mode. We also discuss a method which uses QND measurement to generate small photon Fock states.2. We show that the intracavity dark-state field can be amplified without four-wave mix-ing (FWM) process. By a coherent pumping process, the intensity of the dark-state peak can be significantly amplified and the characteristic three-peak structure remains unchanged. Our experimental results with four-level double A-type of Rb inside an optical cavity agree with the theoretical calculations based on a semi-classical analysis.3. We report both theoretically and experimentally of an atom-cavity system consisting of five-level M-type atoms confined in an optical cavity and coherently coupled from free space by three control lasers. By proper tuning the dressing laser, we found that the ul-tra-narrow cavity line-width can be two order of magnitude than that of the three-type EIT system. The dispersion of the medium steepened is the main factor result in the cavity line-width narrowing.