Novel Experimental Method in the Study of Double Rydberg States by Laser Resonance Excitation

1.IntroductionSequentia1multisteplaserexcitationhasbeenextensivelyusedtostudydoublyexcit-edstatesofa1ka1ine-earthatoms.Mostoftheinvestig8tionsconcernedthedoublyexcitedstatesinwhichoneofthetwovalenceelectronsishighlyexcitedandtheotherisweaklyexcited[1].Inthecasewhenbothvalenceelectronarehighlyexcited(doubleRydbergstates),onlyafewresultswereobtainedduetothelimitutioninexPerimentaltech-nique['j.ThelimitationarosefromvariousaSpectS.First,duringthesequentiallaserex-citationofdoubleRydbergstatesw…     

Field ionization process of Eu 4f~76snp Rydberg states

The field ionization process of the Eu 4f76 snp Rydberg states, converging to the first ionization limit, 4f76s9S4, is systematically investigated. The spectra of the Eu 4f76 snp Rydberg states are populated with three-step laser excitation, and detected by electric field ionization(EFI) method. Two different kinds of the EFI pulses are applied after laser excitation to observe the possible impacts on the EFI process. The exact EFI ionization thresholds for the 4f76 snp Rydberg states can be determined by observing the corresponding EFI spectra. In particular, some structures above the EFI threshold are found in the EFI spectra, which may be interpreted as the effect from black body radiation(BBR). Finally, the scaling law of the EFI threshold for the Eu 4f76 snp Rydberg states with the effective quantum number is built.     

一价镧离子高n里德伯态

基于五步激光共振激发,经由中间态(Xe) 5d6d~3F_2的一价镧离子光谱,分析了该实验谱,确定了一价镧离子一强一弱两个自电离里德伯系列.同时利用多通道量子亏损理论(MQDT)框架下的相对论多通道理论(RMCT)计算,标识了这两个自电离里德伯系列,强的自电离里德伯系列标识为5dnp(5/2,1/2)_3和/或5dnp(5/2,1/2)_2,弱系列标识为为5dnf(5/2,5/2)_3和/或5dnf(5/2,5/2)_2.根据实验谱峰数据,发现有效量子数很高时,里德伯和自电离里德伯能级量子数亏损随激发能量不平滑变化,并分析了可能的原因.     

铯47D精细能级超冷里德堡原子自由演化的动力学研究

用连续窄线宽激光器将超冷铯里德堡原子分别激发到47D_3/2, 47D_5/2精细态, 观察了处于里德堡精细态的铯原子向超冷铯等离子体自由演化的过程, 详细对比了不同精细态的铯里德堡原子预电离时间、电离速率以及等离子体的转化效率. 将里德堡原子快速转化为等离子体的过程解释为局域势阱内由预电离产生的电子与里德堡原子的快速碰撞导致的雪崩电离.     

Entangling quantum gate in trapped ions via Rydberg blockade

We present a theoretical analysis of the implementation of an entangling quantum gate between two trapped Ca⁺ ions which is based on the dipolar interaction among ionic Rydberg states. In trapped ions, the Rydberg excitation dynamics is usually strongly affected by mechanical forces due to the strong couplings between electronic and vibrational degrees of freedom in inhomogeneous electric fields. We demonstrate that this harmful effect can be overcome using dressed states that emerge from the microwave coupling of nearby Rydberg states. At the same time. these dressed states exhibit long-range dipolar interactions which we use to implement a controlled adiabatic phase gate. Our study highlights a route toward a trapped ion quantum processor in which quantum gates are realized independently of the vibrational modes.     

Continuous wave field ionization laser spectroscopy

A new technique is described which allows Doppler-free, isotope-selective excitation of atoms by continuous wave laser radiation and continuous ionization of the atoms by an electric field. The atoms are excited to high Rydberg states in an electric-field-free region of a collimated atomic beam. Because the lifetimes of Rydberg atoms are long they can reach a spatially separated region of the atomic beam where they are ionized by a continuous electric field with a probability of unity. In the case of lithium we obtained a 10³ times larger ion signal by field ionization of Rydberg atoms than by direct photoionization from low excited states.     

电场中Eu原子电离阈移动的实验研究

提出了一种新方法, 精确确定了稀土Eu原子第一电离阈的位置. 先用脉冲电场对Eu原子的高激发Rydberg态进行延时场电离探测, 再通过反向静电场排除光电离和自电离等其他路径所产生的离子信号的干扰, 观察并研究了Eu原子第一电离阈随着电场移动的规律. 由此所确定的零场下第一电离阈的数值与采用其他方法所确定的文献值^{[1, 2]}相一致, 从而验证了该方法的可靠性.     

Rydberg states of hydrogenlike ions in a braneworld model

Precise measurements of optical transition frequencies between Rydberg states of hydrogen-like ions could be used to obtain an improved value of the Rydberg constant, by avoiding the uncertainties about the proton radius. Motivated by this perspective, we investigate the influence of the gravitational interaction on the energy levels of Hydrogen-like ions in Rydberg states in a braneworld model. As it is known, in this scenario, the gravitational interaction is amplified in short distances. We show that, for Rydberg states, the main contribution for the gravitational potential energy does not come from the rest energy concentrated on the nucleus but from the energy of the electromagnetic field created by its electric charge. The reason is connected to the fact that, when the ion is in a Rydberg state with high angular momentum, the gravitational potential is not computable in zero-width brane approximation due to the gravitational influence of the electrovacuum in which the lepton is moving. Considering a thick brane scenario, we calculate the gravitational potential energy associated to the nucleus charge in terms of the confinement parameter of the electric field in the brane. We show that the gravitational effects on the energy levels of a Rydberg state can be amplified by hidden dimensions even when the compactification scale is shorter than the Bohr radius.     

Observation of the Dipole Blockade Effect in Detecting Rydberg Atoms by the Selective Field Ionization Method

The dipole blockade effect at laser excitation of mesoscopic ensembles of Rydberg atoms lies in the fact that the excitation of one atom to a Rydberg state blocks the excitation of other atoms due to the shift in the collective energy levels of interacting Rydberg atoms. It is used to obtain the entangled qubit states based on single neutral atoms in optical traps. In this paper, we present our experimental results on the observation of the dipole blockade for mesoscopic ensembles of 1–5 atoms when they are detected by the selective field ionization method. We have investigated the spectra of the three-photon laser excitation 5S1/2 → 5P3/2 → 6S1/2 → nP3/2 of cold Rydberg Rb atoms in a magneto-optical trap. We have found that for mesoscopic ensembles this method allows only a partial dipole blockage to be observed. This is most likely related to the presence of parasitic electric fields reducing the interaction energy of Rydberg atoms, the decrease in the probability of detecting high states, and the strong angular dependence of the interaction energy of Rydberg atoms in a single interaction volume.     

Microwave spectroscopy of the Zeeman effect in Rydberg atoms of sodium

Experimental results of studying the spectrum of the microwave 37P-37S transition of Rydberg sodium atoms in a weak magnetic field (≤7 G) are reported. The populations of the Rydberg states were measured using the method of selective ionization with a pulsed electric field. When the magnetic field was parallel to the ionizing electric field, a good agreement between the calculated and experimental spectral shapes was observed, making it possible to determine the unknown polarization of the microwave radiation. In the case of the orthogonal configuration of the fields, the resonance structure was suppressed in the field ionization signals due to the strong influence of the magnetic field on the electron trajectories in the detection system.     

丙酮分子的分质量共振多光子电离光谱及多光子电离—离解机理研究

用多光子电离飞行时间质谱法三光子与丙酮分子３ｄ形态和４ｓ态共振的激光波长区域获得了丙酮分子的共振多光子电离分质量多光子电离（ＭＰＩ）光谱和飞行时间质谱，实验观察到的主要产物是ＣＨ３ＣＯ＾＋和ＣＨ＾＋３，还观察到了少量的Ｃ＾＋，ＣＨ＾＋，ＣＨ＾＋２和ＣＨＯ＾＋，在实验的激光波长范围内未见到母体离子，分质量多光子电离光谱具有相似的光谱结构，几个主要谐峰分别对应着（ｎ０，３ｄ）和（ｎ０，４ｓ）里德堡跃迁     

Measurement of quantum defect of nS and nD states using field ionization spectroscopy in ultracold cesium atoms

<正>This paper reports that ultracold atoms are populated into different nS and nD Rydberg states(n=25~52) by two-photon excitation.The ionization spectrum of an ultracold Rydberg atom is acquired in a cesium magneto-optical trap by using the method of pulse field ionization.This denotes nS and nD states in the ionization spectrum and fits the data of energy levels of different Rydberg states to obtain quantum defects of nS and nD states.     

Na原子高里德堡态的辐射寿命

用可调谐激光两步激发Ｎａ原子高激发发里德堡态布居，在光激发后施加脉冲电场测量激发态的场电离阈，利用阈值电场和延迟场电离方法测定了ｎｓ（ｎ＝２０～２４）和ｎｄ（ｎ＝１９～２３）态的寿命值，并与计算值进行了比较，对影响寿命的因素作了讨论。     

One-dimensional Rydberg gas in a magnetoelectric trap

We study the quantum properties of Rydberg atoms in a magnetic Ioffe-Pritchard trap which is superimposed by a homogeneous electric field. Trapped Rydberg atoms can be created in long-lived electronic states exhibiting a permanent electric dipole moment of several hundred Debye. The resulting dipole-dipole interaction in conjunction with the radial confinement is demonstrated to give rise to an effectively one-dimensional ultracold Rydberg gas with a macroscopic interparticle distance. We derive analytical expressions for the electric dipole moment and the required linear density of Rydberg atoms.     

Three photon resonant ionization in atomic potassium via S,P, D and F series Rydberg states

Single colour three photon resonant ionization (2 + 1) is observed in atomic potassium vapour in a heat pipe oven using an excimer laser pumped dye laser. Using wavelengths between 570 nm and 603 nm various²S and²D Rydberg states are populated by two photon excitation. Third photon of the same wavelength ionizes the atoms. Rydberg states up ton ⋍ 50 are observed. Electric field as low as 1 V/cm causes extensive Stark mixing of the states. This results in progressively higher three photon ionization signals via the perturbed²P and²F Rydberg states. The three photon ionization process is studied using both linearly and circularly polarized incident light. The experiment shows qualitatively that the²P Rydberg states are perturbed primarily by the²D states in the prescence of an external electric field and to a much smaller extent by²S states. This is also explained theoretically by calculating the Stark mixing coefficients under the Bates and Daamgard (1949) approximation. Implication for a similar effect in other alkali elements is discussed.     

Correlation of momenta of electrons and the nucleus in atoms

The process of resonant multiphoton ionization of a hydrogen atom in the ground 1s state is studied by direct numerical integration of the nonstationary Schrödinger equation for a quantum system in an electromagnetic field. The dependence of photoionization probability on the radiation intensity is found to be nonmonotonic. It is established that the minima of ionization correspond to multiphoton resonances between the ground state and one of the excited (Rydberg) atomic states perturbed by the laser field. It is shown that ionization is suppressed due to rearrangement of Rydberg states in a strong electromagnetic field and is accompanied by efficient Raman Λ transitions, which connect a set of closely lying Rydberg states via the continuum.     

Ionization of fast rydberg atoms in longitudinal and transverse electric fields

The main properties of longitudinal and transverse electric field ionizers for fast Rydberg atoms n=21–40 have been investigated. The dispersion and the background due to collisional processes between fast atoms and residual gas molecules have been measured and calculated. The kinetic energy spread of ions formed by field ionization of Rydberg atoms and their trajectories have been calculated. The potassium beam energy was 3.9 keV.     

Yb原子高激发能级的跃迁特性

采用“类氢”模型,用数值积分方法计算了Yb原子部分高激发Rydberg态和Stark态的自发跃迁概率,及环境黑体辐射引起的受激跃迁概率,并与采用延迟脉冲场电离方法对相应态的测量结果做了比较.选取典型的初始态,测量了环境黑体辐射引起的受激跃迁对周围能级的再布居特性,并给出了理论解释.对“类氢”模型应用于复杂原子的适用性进行了分析. 关键词：     

Measuring the degree of unitarity for any quantum process

The state transfer from cesium nS (n = 45?53) states to Stark (product) states induced by a weak electric field (WEF) pulse was investigated using the state-selective field ionization method in a standard magneto-optic trap (MOT). The WEF pulse shifts the nS Rydberg states that anticross with the (n ? 4) hydrogen-like manifolds, causing state transitions from the initial excited nS state to the Stark states. The mechanism of transfer was investigated by changing the rising and falling time of the WEF pulse and the switching off time of the external field pulse had an important role during the evolution process of product states. The population of the product states is also measured as a function of the principal quantum number and Rydberg densities.