Investigation On Quantum Coherent Control Via Incoherent Collisions

Recently, quantum coherent control has attracted considerable interest due to its extensive applications, such as to obtain ultrahigh-resolution spectroscopy and frequency metrology, to control molecular motion and chemical reactions, to get information on atomic or molecular excited states, to achieve coherent rapid adiabatic population transfer, and to realize quantum computation and quantum information processing. There exist two kinds of quantum interferences which underlie quantum coherent control. One refers to the interference between two or more different transition pathways connecting the same initial or final state in the frequency domain, and the other refers to the interference between two or more time-separated transition pathways connecting the same initial and final states in the time domain. In this thesis, we try to theoretically and experimentally investigate collision-induced quantum coherent control in both the time and frequency domains in atomic multi-level system and atom-molecule hybrid system to find the conditions for generating quantum coherent control, and the dependence of quantum coherent control on the environmental conditions.In the case of quantum coherent control in the time domain, we report the experimental observation of the quantum interference between two time-delayed 3P-5S (or 4D) transition pathways realized through the atomic collision-assisted two-step excitation and atom-molecule hybrid excitation by a single nanosecond laser pulse in the Na₂-Na system. By solving the time-dependent Schr(o|¨)dinger equation, we study the effects of the ratio of the two collision-assisted transition probabilities, collision energy transfer rate, and collision-induced decay rate of the 5S (or 4D) state on the interference fringes. It is clearly shown that temporal coherent control of quantum amplitudes can be realized through the incoherent collisions.In the case of quantum coherent control in the frequency domain, we theoretically study the collision-induced destructive interference in an open rhomb-type five-level system with a widely-separated doublet. By using the density...