Effect Of Quantum Interference In A Multi-level System

Quantum interference in quantum optics has been discussed extensively recently,many interesting phenomena have been observed due to quantum interference amongmulti-channels in multilevel atomic systems. In this thesis, by means of quantumoptics theory, we have intensively investigated the problem theoretically, and a seriesof meaningful results are obtained.Quantum interference breaks through the traditional bottleneck while leadinginto the superposition principle in quantum mechanics, it makes important progress infields such as microelectronic manufacturing process, mere electronic device,quantum information, quantum communication encryption and light quantumcomputer, etc. This thesis is based on the Supervisor's National Natural ScienceFoundation of China" nonlinear effects at the low light levels "and "a relevant studyof the new mechanism on lasing in random media", we have studied many kinds ofphysical phenomena on the basis of quantum interference. The key points of thisthesis are presented as follows:1. Overview and the tendency of the effects of quantum interference.2. Making an analysis of relevant research approaches, tool foundations of the theory.3. Investigating a Y-type four-level atom interacting with external fields system. It isshown that increasing the control field can reduce the probe absorption, theelectromagnetically induced transparency and gain can be obtained if the parametersare taken appropriately. An interesting phenomenon is found that the system appearsto be probe gain in a large region if the external fields Rabi phases are takenappropriately.4. The quantum interference effects of a Quasi- A-type four-level atom system withtwo light fields is studied. When the probe field is weak, along with the change ofRabi frequencies of driving field, the system appears to be hole burning in dispersioncurve, and two big EIT windows having approximately the same width areinvestigated. In addition, the evolution of dispersion with the Rabi phase of probe field displays the optical bistability.5. In chapter five, we report the effects of Vacuum-Induced Coherence in alaser-driven four-level atom consisting of three near-degenerate upper levels have anadditional coherence term due to interaction with the vacuum of the radiation field.We show that such coherence preserves electromagnetically induced transparencyand optical bistability phenomena. The dynamical behaviors of the populationdistribution via Vacuum-Induced Coherence was analyzed numerically too.