【作者】 王勇；

【导师】 赵建明；

【作者基本信息】 山西大学 ， 光学， 2015， 硕士

【摘要】 里德堡原子是指具有很高主量子数n的高激发态原子。相比于基态原子,里德堡原子具有独特的性质。例如：里德堡原子间具有很强的长程范德瓦尔斯相互作用以及偶极相互作用,阻止了相邻原子的进一步激发,产生了激发阻塞效应,可用于实现单里德堡原子的激发。里德堡原子的极化率非常大,很小的电场就可以产生里德堡态能级的频移。里德堡原子有很长的寿命,很大的电偶极矩和轨道半径,这些特性使里德堡原子称为研究量子逻辑门的备选介质,在原子分子物理的研究中经久不衰。本文中,我们利用里德堡原子极化率大、对电场非常敏感的特点,在制备超冷里德堡原子的基础上,增加外电场,研究里德堡原子在外加电场中的S触效应,初始制备的万S里德堡态与(n-4) Stark多重态之间的态混合效应以及机制。实验中我们以碱金属铯原子为研究对象。在激光冷却和俘获冷原子的基础上,通过6S1/2→6P3/2→nD/nS的两步激发制备超冷里德堡原子。通过施加一个脉冲电场电离里德堡原子,探测其离子信号来记录实验数据。首先,我们根据理论计算的Stark能级图,获得49S态原子与附近Stark能级的回避交叉的中心电场和能级间隔等参数。在实验上测量回避交叉附近的离子谱,结果表明实验结果与理论吻合的很好。然后,在制备nS里德堡原子后,施加外加电场,观测到了由nS里德堡原子经避免交叉跃迁到高-l态的现象,发生态转移,即产生高-l态信号。我们改变脉冲电场的强度测量了nS态到高-l态的转化率,研究了态转移机制。结果表明随着脉冲电场的增加,高-l态的转化率先急剧增加到饱和然后缓慢下降。最后,我们改变电场使之通过一个特定的回避交叉点,改变电场通过避免交叉点速度研究里德堡原子经避免交叉点时的绝热／非绝热过程；改变延迟时间来改变相互作用时间研究高-l态里德堡原子之间的相互作用会引起的m-mixing效应和penning电离。结果表明相互作用时间越多,m-mixing效应越强。同时测量了自由离子随相互作用时间的变化情况,证明了m-mixing效应的存在。本文的创新之处：1.研究了电场条件下里德堡能级的避免交叉,得到了回避交叉处的中心电场,实现了电场操控的态转移现象,实验测量与理论模拟相一致。2.研究了电场作用下高-l态的转化率,由于m-mixing效应高-l态的转化率随外加电场的增大先急剧增大到饱和然后下降。m-mixing效应增加了高-l原子的相互作用,导致了超冷等离子体的产生。更多还原

【Abstract】 Rydberg atom is the highly excited atom with a high principal quantum number n. Compared to the ground state atom, Rydberg atom has many features. For examples: Rydberg atoms have strong long-range Van der Waals interactions and dipole interactions, which offers many facilities in search of the dipole blockade effect and achievement of the excitation of a single Rydberg atom; Rydberg atoms have a large polarizability and very sensitive to an external electric field, leading to Stark effect; Rydberg atoms also have a long lifetime, large electric dipole moment and giant orbit radius, which make Rydberg an idea candidate of the quantum gate and being the hot topic in the research of the atomic and molecular physics.In this paper, we study the electric fields induced Stark effect and state-mixing effect between initially nS state and (n-4) stark manifolds.In our experiments, we choose alkali metal cesium atoms as the research sample. The ultracold cesium atoms are excited to Rydberg states via 6S1/2→6P3/2→nD/nS two-photon transition in a standard magnetic trap. The state selective field ionization is employed to ionize prepared Rydberg atoms and released ions are detected with a calibrated macro channel plate detector.Firstly, according to the theoretical calculation of Rydberg stark structure, we obtain the parameters of the avoided crossings, such as center field and energy gap. The ion spectroscopy near the avoided crossing is experimentally measured, which is agree well with the calculations.Secondly, after preparing the nS Rydberg atoms in the MOT, we apply an external electric field and obtain high-1 state when electric field through the avoided crossing formed between the nS and near (n-4) Stark state. We have measured the transfer rate as a function of the amplitude of the electric field and investigated the transfer mechanism. The results show that the measured transfer rate of high-1 is creasing as the electric field and get to the maximum, after that begin to decrease.we we measure the transferred high-l Stark states as a function of the strength of electric-field pulse. The measured signal of high-l Stark states increased to saturated then decreased with electric field increase. We think the strong interaction between high-l Rydberg atoms causes penning ionization and m-mixing effect.Finaly, we focus on a specific single avoid crossing to investigate the adiabatic/diabatic passage when the electric field ramp through the selected avoided crossing. We change the ramp time and delay time and measured the high-1 state, which shows that the m-mixing effect has an important role in the detection of the high-1 state. The free ions due to the interaction between Rydberg atoms are also measured as a function of the delay time, which proves the existence of m-mixing effect.The innovations of this work are shown two aspects as followed:1.We have studied the avoiding crossing of Rydberg atom’s energy level in the condition of the electric field and got the value of electric field in the center of avoiding crossing. The state mixing and transfer through avoided crossing have being obtained experimentally and the measurement is consistent with the theoretical simulation.2. The transformation of high-l state with the electric field have been investigated. We find that the transfer rate of high-l state increase to saturation and after that shown decrease trend with the increase of electric field, which is attributed to the m-mixing effect. The strong interaction between high-l Rydberg atoms caused penning ionization and to form the plasma.更多还原