Quantum control of cold alkali atoms by using hybrid temporal-spectral pulse shaping = 시간-주파수 복합적인 펄스 재단을 이용한 저온 알칼리 원자의 양자 제어

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Quantum control of alkali atoms in ensemble is studied by using broadband pulse shaping schemes in both spectral and time domain. In the weak field regime, interference between two two-photon excitation passages of a four-level system of the rubidium atom in a diamond configuration was considered. Eight spectrum blocks were classified by inherent phase jumps of transition probability amplitude components and a condition for maximal constructive interference was predicted by second order time dependent pertubation theory. Experiments carried out with spectrally phase-coded laser pulses show good agreement with the theoretical prediction. In the strong field regime, quantative analysis on ensemble averaged Rabi oscillation was conducted to investigate spatial inhomogeneity of interaction. By using the ultrafast laser interaction with the cold atomic rubidium vapor spatially confined in a magneto-optical trap, the oscillatory behavior of the atom excitation is probed as a function of the laser pulse power. Theoretical model calculation predicts that the oscillation peaks of the ensemble averaged Rabi flopping fall on the simple Rabi oscillation curve of a single atom and the experimental result shows good agreement with the prediction. We also test the three-pulse composite interaction $R_x(\pi /2)R_y(\pi)R_x(\pi /2)$ to develop a robust method to achieve a higher fidelity population inversion of the atom ensemble. Based on quantative analysis of inhomogeneity of interaction, dynamics of a two-level system induced by a chirped pulse with a spectral hole and a temporal hole were respectively explored in both theoretically and experimentally. When a spectral hole is made, the pulse is called a chirped zero-area pulse. By a chirped zero-area pulse, CPR and CPI of a two-level system takes place even there is no resonant spectrum. Theoretical investigation showed that the dynamics can be modeled by a three-step evolution, $R_\varphi (\Theta_2)R_z($\Theta_1)R_{\pi + \varphi} (\Theta_2)$, where the first and the third are by Rabi oscillation and the second is an adiabatic evolution. The CPR and CPI dynamics is turned out to be a result of interplay between adiabatic evolution and Rabi rotations: CPI and CPR occur when adiabatic evolution makes two rabi rotations completely constructive or destructive. On the other hand, when a temporal hole is made on a chirped pulse, the system only begin with a superposition state shows probability oscillation, even to 0 or 1. The probability oscillation for this case is also by interplay between adiabatic evolution and Rabi rotation: the adiabatic evolution applies phase on a superposition state and the Rabi rotation mixes it. The probabilities of 0 or 1 occur when the interference is maximized. The studies on a chirped pulse with a temporal hole and a spectral hole showed that the hole can be a new control method of quantum control in strong field regime.
Ahn, Jaewookresearcher안재욱researcher
한국과학기술원 :물리학과,
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학위논문(박사) - 한국과학기술원 : 물리학과, 2017.2,[ix, 75 p. :]


pulse shaping; quantum control; coherent control; 펄스 재단; 양자 제어; 결맞음 제어

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