Quantum Coherent Manipulation On Dynamic Propagation Properties Of Monochromatic Optical Fields In Cold Atoms

The interaction of the light with atoms, as a very important research content of the quantum optics, has thriving development in recent decades. Based on the generation of the interaction of coherent light with atomic medium, atomic coherence effects have received increasing attention. Studies on the coherent photon-atom interaction at quantum level have enhanced the development of quantum mechanics, and given birth to a new interdisciplinary field bridging quantum optics and information technologies. In this thesis, we find several exciting and unexcepted results in quantum optical systems by using the atomic coherence.This thesis mainly focuses on atomic coherence effects related phenomena in various systems involving multilevel atoms. Based on atomic coherence effects, such as electromagnetically induced transparency(EIT) and stimulated Raman adiabatic passage(STIRAP), this thesis mainly introduces the physical methods, research background and recent developments related to the accumulation of arbitrary Berry phase, two-color nonreciprocity, storage and retrieval of photons, and so on. All of these may provide a more reliable theory for experimently constructing the effective phase gate, the optical diodes and the optical switch, and lay a solid foundation for the practical application of quantum information.In the third chapter, we propose and analyze a feasible scheme for achieving geometric Berry phases via the efficient technique of fractional stimulated Raman adiabatic passage(f-STIRAP) in the typical Λ coherent cold atomic system. Experimental implementations of QI algorithms suffer from inaccuracies in the gate operations, which reduce the fidelity of QI processing. Unlike standard STIRAP,f-STIRAP allows the creation of any preselected coherent superposition of the intial and final states. Note, As accumulation of a Berry phase needs in a cyclic evolution path, we carefully design two reversed f-STIRAP processes. Then, we can control the Berry phase by the accurately designed mixing angle of pump and Stocks. And because the evolution paths of population and the ultimate values of Berry phase are not sensitive to the pulse duration and the pulse delay, we can pulse duration and pulse delay may also be modulated to accumulate a desired Berry phase by controlling the intermediate dark states. The technique can be easily extended to other multi-level systems with a little more complicated pulse sequences applied to bring convenience to the quantum computer and rapidly generate some quantum gates.In the fourth chapter, We study the two-color nonreciprocal effects of transmission and reflection in cold atoms driven into the tripod configuration and confined in a moving optical lattice. Compared with previous work, we choose a more reasonable atomic density distribution in experiments and a lower atomic speed of 3 m/s in the optical lattice. As expected from the Doppler effect, the optical response of a moving atom will be changed. The main manifestation is that the probe susceptibility will experience a frequency shift along the direction of motion. The probe transmissivity and absorption coefficient of the moving atomic ensemble will be changed due to the Doppler frequency shift experienced by the probe susceptibility. Our numerical results show that a very high contrast of the forward-backward transmission up to around 92%(reflection up to around 85%) is observable near the sharp edges of two tunable PBGs. And the such two-color optical nonreciprocitycan be dynamically manipulated by varying the driving and coupling field detunings, the probe pulse length, the atomic lattice velocity, etc. The transmission nonreciprocity can be used to produce optical diodes or optical isolators, while the reflection nonreciprocity can be used to design invisible metamaterials. The technique shown here could be easily extended to other multilevel systems with multicolor nonreciprocal effects.In the fifth chapter, we study how to stop and regenerate a pair of single-photon pulses at adjacent locations and provide a realistic picture for photon-photon interactions in coherently prepared Rydberg atomic ensemble. A majority of the previous works about Rydberg EIT are based on the picture of steady-state propagation of a light. However, we provide an efficient approach to such complicated quantum dynamical processes in Rydberg medium. Such dynamical process can become rather complicated due to the ever-changing interaction between photon pulses, which is found to be capable of changing their absorption and dispersion significantly even in the perturbative regime. Our numerical results show that when two photons get close to each other in Rydberg EIT medium, there will exist different scenarios, not always the commonly known Rydberg blockade leading to a two-level medium. The similar processes involving stopped photons can be applied to implementing photon switchers and photon-photon gates. The other related problems, such as the converted spinwave profiles under inhomogeneous interaction, the difference between adiabatic and non-adiabatic passages for stopping photons, as well as the appropriate ways to stop and regenerate photons under different circumstances, are also investigated in our approach. Providing the optimal strategies for implementing photon transistors and photonic gates, the understanding of the processes could be valuable guide for the relevant experimental researches.