The Study Of Quantum Coherent Transient In Λ System

On the basis of quantum mechanics and experiments of Electromagnetically Induced Transparency (EIT), aΛ-three-level system configuration and a quasic-Λ-four-level system configuration are considered in this thesis. By numerically solving the corresponding equations of motion of the density matrix, the time-dependent probe response of an EIT and a single EIT window to double EIT windows are studied theoretically. And based on them, the optical switching property in the above both system configurations are also discussed. It is worth noting that the perturbation theory used commonly in solving density matrix equation is not employed in this thesis, thus the results fit situation which field has any strength.Firstly, The coherent transient property of an EIT inΛ-three-level configuration is studied comprehensively in this thesis. There is a coherent transient process with high quantum beats in the absorptive spectra. Then, the EIT transient properties with different probe frequencies are studied as function of Rabi frequency of both couple field and probe field. It shows that the frequency of dressed state quantum beats is mainly determined by the couple field, while the frequency of dressed state nutation is mainly determined by the probe field.Secondly, the coherent transient property of an EIT subject to a RF field driving a hyperfine transition within the ground state in a quasi-A-four-level configuration is studied, and a theoretical study of the time-dependent probe response of a single EIT window to double EIT windows is also made by numerically solving the equations of motion of the density matrix. There is also a coherent transient process with high quantum beats. This effect can be explained using the dressed state formalism. The quantum beats result from quantum coherence effect between the levels driven by RF field. The results show that when the probe field is on resonance with a bare-state transition, the beat frequency is one-half of RF Rabi frequency in transient absorption response. While the probe field is on resonance with a dressed-state transition, which results from the atom system interact with strong RF field, the beat frequency equals the RF Rabi frequency in transient absorption response.Finally, the optical switching property in the A-type configuration three or four level system is studied. Optical switching of the probe field can be achieved by applying a pulsed coupling field or RF field and both of them have their own advantage in A system. The speed of the optical switching of three-level system is much faster than that of four-level system, while the depth of the optical switching of the latter is much larger than that of the former. The speed of optical switching of the two systems can be increased by increasing Rabi frequency of coupling field or RF field. The results will provide benefits for experiment research of optical stitching equipment.