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Theoretical Study of Decelerating Polar Molecules by Microwave in Waveguide

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Tutor: HuZhongKun
School: Huazhong University of Science and Technology
Course: Theoretical Physics
Keywords: cooling molecules,AC-Stark effect,Stark decelerator,microwave lattices
CLC: O561
Type: Master's thesis
Year:  2011
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Excited by the successful cooling of atoms that has revolutionized atomic physics and quantum optics in the past two decades, cold molecules are also being very actively explored currently. Molecules offer microscopic degrees of freedom absent in atomic gases, resulting in unique properties that may allow for the study of new physical and chemical phenomena. A necessary prerequisite for these applications is the ability to obtain cool heteronuclear molecular samples prepared in their electronic and vibrational ground state.It is very difficult to extend the laser-cooling techniques to molecules because of the complex molecular energy structures. However, several techniques for cooling or decelerating molecular samples have been investigated. In this thesis, firstly, the basic principle, experimental reslts and the recent progress on cooling of neutral molecules have been briefly introduced. Secondly, we study the basic idea and the recent progress on microwave manipulation of neutral molecules in detail.At last we propose a microwave method to decelerate polar molecules from buffer gas cooling beam using traveling microwave lattice in waveguide. The basic idea builds on the first-order AC-Stark potential, which relies on the interaction between the microwave fields and the rotational structure of molecules. Two counter-propagating microwave fields with frequency modulation interfere and create the moving microwave lattices. We trap the molecules at the antinodes of microwave lattices using red detuning. When gradually reducing the modulation frequency the velocity of the potential wells simultaneously reduce, so do all trapped molecules. The numerical trajectory simulation on the deceleration of MgO molecules is carried out. Over the 0.5m length of deceleration area, MgO molecules in rotational ground state with an initial velocity of 120m/s can be brought to a standstill, cresponding acceleration a = - 1.44¡Á10~4 m/s~2. The phase-space acceptance volume is [4mm¡Á8m/s]¡Á[3mm¡Á6m/s]~2 and the resultant temperature of molecules is 60mK.
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