| Quantum coherent control has attracted considerable interest in recent years, whichmanipulates the dynamics of atomic or molecular systems in a particular initial state forobtaining the needed state by using a single laser pulse or some pulses. Now, temporal coherentcontrol (TCC), stimulated Raman adiabatic passage (STIRAP) and chirped adiabatic passage(CHIRAP) are three widely used ones of many ways to control population transfer betweenparticular quantum states. In this dissertation, we propose some selective and efficient ways torealize control of population transfer and creation of coherent superpositions between quantumstates by merging the advantages of the above mentioned three methods. The main achievementsand innovations are as follows:First, we show that by using a pair of counterintuitively ordered chirped pump-Stokespulses, selective and complete population transfer from either of the equally populated initialdoublet states to the final state in a ladder-type four-level system can be realized via STIRAP andCHIRAP when the pulse bandwidth is smaller than about1/10of the energy separation betweenthe doublet states. Moreover, we further demonstrate that the spectral resolution of selectivepopulation transfer can be enhanced significantly by using a pump pulse pair and Stokes pulsevia STIRAP and TCC.Second, we investigate the selective and efficient population transfer in a Λ-type five-levelsystem with equally populated initial and empty final doublet states by a pair ofcounterintuitively ordered chirped pump-Stokes pulses. It is shown that population can beselectively and completely transferred from either of the equally populated initial doublet statesto either of the final ground doublet states by merging STIRAP and CHIRAP when the pulsebandwidth is smaller than about1/10of the energy separations between the initial doublet statesand between the final doublet states.Third, we propose a way to significantly enhance the selectivity and efficiency of coherentpopulation transfer in a Λ-type four-level system with closely spaced final doublet states by a train of counterintuitively ordered pump-Stokes pulse pairs created through optical delay line. Itis shown that the spectral resolution of selective and perfect population transfer to either of thetarget states can be improved more than one order of magnitude as compared to the commonlyused STIRAP technique due to temporal constructive and destructive quantum interferencebetween the sequential transitions and subsequent coherent accumulation and annihilation in thetime domain. Moreover, an arbitrary coherent superposition between the closely spaced finaldoublet states can be created by suitably tuning the repetition period and detuning of the laserpulses. In addition, the spectral resolution of selective and perfect population transfer to either ofthe target states can be improved significantly by using the pump-Stokes pulse sequencesproduced by using sinusoidal spectral phase modulation of the ultrashort pulses in the frequencydomain with a spatial light modulation in the4f configuration.Fourth, we present a scheme for control population transfer and arbitrary superpositions ofquantum states with a single chirped laser pulse in a Λ-type excited-doublet four-level system. Itis shown that when the pulse bandwidth is smaller than about1/10of the the energy separationsbetween the excited-doublet levels and between the ground states, selective, efficient and robustpopulation transfer from the initial state to the target states (whether excited state or ground one)can be achieved via CHIRAP. Moreover, arbitrary coherent superpositions between any twostates of the three target ones can be created by appropriately tuning the chirp rate and detuningof the laser field.The achievements of this dissertation provide effective solutions to the further research oncontrol of population transfer and have great potential applications in quantum informationprocessing, control of chemical reactions and laser cooling technology. |
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