【作者】 王鹏军；

【导师】 张靖；

【作者基本信息】 山西大学 ， 光学， 2011， 博士

【摘要】 本论文以玻色子87Rb和费米子40K在磁阱中实现了量子简并为基础,研究了超冷原子的大范围转移,从QUIC阱转移到向玻璃气室的中心；在绝热展开量子简并费米气体的基础上研究了费米子的瑞利超辐射；搭建了远失谐的交叉偶极力阱,实现了混合气体的绝热转载,实现了光阱中玻色费米气体的量子简并,结合微波射频制备原子超精细态的技术,观测到了玻色子87Rb和费米子40K的s-,p-,d-波的Feshbach共振,实现了原子之间相互作用的精细调节。简要地描述了实验上在磁阱中实现玻色费米气体量子简并的冷却过程,介绍了实验上需要的光学系统,计算机控制系统,磁场系统和微波射频装置。主要就QUIC组合线圈的设计工作,以及实验结果与理论计算的对比作了详细叙述,然后讨论了玻色气体和费米气体在进入量子简并区域的不同实验现象,以及实验上BEC和DFG的实验判据。BEC的实验判据很明显,就是飞行吸收成像中原子密度分布的各向异性和bimodal的存在；而费米气体的量子简并度有专门的参数衡量,没有像BEC一样明显的判据,要通过对实验数据进行拟合才能得到准确的原子云信息。最后详细研究了在QUIC阱中,用玻色子87Rb作为中间媒介来共同冷却费米子40K达到量子简并的情况,分别讨论了蒸发冷却中微波和射频的作用。实验中发现87Rb原子的另一个超精细态原子的存在严重影响了费米子的冷却效果,我们提出了一种结合微波和射频共同作用的冷却机制,提高了蒸发冷却的效率。针对超冷原子大范围转移的困难,我们采取了两种方法来克服,即利用重力方向的磁场抵消重力和加大重力方向磁阱的束缚减小重力的影响。实验上采用上述方法水平转移超冷原子达到12mmm,最后应用一个巧妙的磁场跳跃实现了原子振荡的压缩。这种转移的方法可以叠加使用,用作原子更大范围内的转移；转移过程中原子加热不明显,不会导致大量的原子损耗。本论文还介绍了稀薄超冷简并费米气体中的集体原子反冲行为。通过应用一个绝热可控展开将得到量子简并的费米气体进一步动量压缩,然后采用一束垂直偏振泵浦光照射原子云。我们首次在实验上观测到了费米气体的瑞利超辐射现象,证明了超辐射与原子所服从的量子统计没有关系。实验上观测到的许多实验现象期待进一步的理论解释。应用射频微波绝热转移将超冷原子制备在各自的绝对基态上,在0G到600G的范围内扫描磁场,观测到了10个Feshbach共振,包括6个同核共振,四个异核共振,其中有s-,p-,d-波的Feshbach共振。为了精确测量共振的位置,实验上测量了原子的损耗和加热,通过理论拟合得到了共振的位置,宽度等信息。实现了精确调节原子之间的相互作用。更多还原

【Abstract】 In this thesis, the experiment allowing for the creation of large mixtures of quantum degerate fermionic 40K and bosonic 87Rb are firstly presented. The design, construction and the apparatus are briefly described here. More detailsfocus to the designs of three coils for the QUIC trap. At low temperature, both the Bose and Fermi gases are expanded relative to a classical gas at the same temperature. For fermions, however, this effect is due to the Pauli exclusion principle rather than atom-atom interactions. While in Bose case a phase transition separates the degenerate and classical regime, a trapped Fermi gas undergoes a gradual crossover between the classical limit and the compact Fermi sea.We have transport horizontally lot of ultracold atoms over a distance of 12mm in a harmonic trap. By using a horizontal homogeneous magnetic field in the direction reverse to the QUIC trap to decrease the bias field, we achieve a enough radial frequency providing strong confinement in order to hold the atoms against gravity for the whole transport distance. We demonstrate suppression in the oscillation of the atomic clouds using a technique based on the interaction between the atom and the homogeneous magnetic field in the final transport. This transport technique avoids the heating and loss induced by the mechanical noise and might have applications in transporting larger distances with quantum degenerate mixed gases.We demonstrate clear collective atomic recoil motion in a dilute, momentum-squeezed, ultra-cold degenerate fermion gas by circumventing the effects of Pauli blocking. Although gain from bosonic stimulation is necessarily absent because the quantum gas obeys Fermi-Dirac statistics, collective atomic recoil motion from the underlying wave-mixing process is clearly visible. With a single pump pulse of the proper polarization, we observe two mutually-perpendicular wave-mixing processes occurring simultaneously. Our experiments also indicate that the red-blue pump detuning asymmetry observed with Bose-Einstein condensates does not occur with fermions.Homonuclear and heteronuclear Feshbach resonances have been used in order to change the interaction properties of the mixture in a controlled fashion. We report the experimental preparation of the absolute ground states by means of the radio-frequency and microwave adiabatic rapid passages and the observation of magnetic Feshbach resonances in the ultracold mixture between 0 and 600 G, including 6 homonuclear and 4 heteronuclear Feshbach resonances. The resonances are identified by the abrupt trap loss of atoms induced by the strong inelastic three-body collisions. These Feshbach resonances should enable experimental control of the interspecies interactions.更多还原