The lifetime of the 3d^2D_5/2-level in singly-ionized calcium has been measured by the electron-shelving technique on different samples of rf trapped ions. The metastable state has been directly populated by exciting the dipole-forbidden 4S_1/2 - 3D_5/2 transition. In ion clouds, the natural lifetime of this metastable level has been measured to be (1095+-27) ms. For the single-ion case, we determined a lifetime of (1152+-20) ms. The 1sigma-error bars at the 2%-level have different origins for the two kinds of experiments: data fitting methods for lifetime measurements in an ion cloud and control of experimental parameters for a single ion. De-shelving effects are extensively discussed. The influence of differing approaches for the processing of the single-ion quantum jump data on the lifetime values is shown. Comparison with recent measurements shows excellent agreement when evaluated from a given method.
We present an experimental scheme which combines the well established method of velocity-mapimaging, with a cold trapped metastable neon target. The device is used for obtaining the branching ratios and recoil-ion energy distributions for the penning ionization process in optical collisions of ultracold metastable neon. The potential depth of the highly excited dimer potential is extracted and compared with theoretical calculations. The simplicity to construct, characterize and apply such a device, makes it a unique tool for the low-energy nuclear physics community, enabling opportunities for …
In a joint experimental and theoretical endeavour, photoionization of metastable C4+(1s 2s 3S1) ions via intermediate levels with hollow, double-K-vacancy configurations 2s2p, 2s3p, 2p3s, 2p3d, 2s4p, 2p4s and 2p4d has been investigated. High-resolution photon-ion merged-beams measurements were carried out with the resolving power reaching up to 25,000 which is sufficient to separate the leading fine-structure components of the 2s2p 3P term. Many-body perturbation theory was employed to determine level-to-level cross sections for K-shell excitation with subsequent autoionization. The resonance …
Relativistic evaluation of the two-photon decay of the metastable ${1s}^{2} 2s 2p~^3\mbox{P}_0$ state in berylliumlike ions with an active-electron model
We present a kinetic model for optical pumping in Lu$^+$ and Lr$^+$ ions as well as a theoretical approach to calculate the transport properties of Lu$^+$ in its ground $^1S_0$ and metastable $^3D_1$ states in helium background gas. Calculations of the initial ion state populations, the field and temperature dependence of the mobilities and diffusion coefficients, and the ion arrival time distributions demonstrate that the ground- and metastable-state ions can be collected and discriminated efficiently under realistic macroscopic conditions.
Metastable level properties of the excited configuration $4p^{6}4d^{8}4f$
研究了类铑离子基态组态$4p^{6}4d^{9}$和激发组态$4p^{6}4d^{8}4f$和$4p^{5}4d^{10}$的亚稳能级。在准相对论Hartree-Fock近似下，采用基于准相对论变换径向轨道的广义组态相互作用，用{ \sl ab initio}方法计算了能级能量、辐射多极跃迁几率.研究了从$Z=60$到$Z=92$的离子的亚稳能级辐射寿命的系统变化趋势。证明和讨论了高多极级（$M2$和$E3$）辐射跃迁对计算辐射寿命的意义。
The objective of our proposal is to study the photoionization of Chlorine, Sulfur, and Phosphorus ions using the unique high resolution capability of 10.0.1 beamline in the ALS. These species are relevant in astrophysics and as a benchmark for state of the art theoretical models of the quantum properties of ions. We also propose to test a technique to quench the metastable states from the ion-beam based on recent experimental evidence and on a well known technique in chemistry. The work of this proposal may lay the foundations for a definite solution to control the metastable component of the …
Precision isotope shift measurements in Ca$^+$ using highly sensitive detection schemes
我们展示了一种有效的高精度光谱技术，为单囚禁离子与非封闭的过渡。在双搁置技术中，单个光子的吸收首先被放大到与不同种类的共捕获冷却离子共享的正常运动模式的几个声子，然后使用标准电子搁置技术被进一步放大到由冷却离子发射的数千个荧光光子。我们采用这种扩展的光子反冲光谱技术进行第一次高精度的绝对频率测量的$^{2}$ D $_{3/2}$ $\rightarrow$ $^{2}$ P $_{1/2}$过渡的$^{40}$钙$^{+}$，导致在$f=346\, 000\, 234\, 867(96)$ kHz的过渡频率。此外，我们确定了该跃迁的同位素位移和$^{2}$ S $_{1/2}$ $\rightarrow$ $^{2}$ P $_{1/2}$跃迁的$^{42}$ Ca $^{+}$，$^{44}$ Ca $^{+}$和$^{48}$ Ca $^{+}$离子相对于$^{40}$ Ca $^{+}$的精确度低于100 kHz。改进的场和质量移动常数的这些过渡，以及在均方核电荷半径的变化提取从这个高分辨率的数据。
Derivations for the higher tensor components of the quadrupole polarizabilities are given and their values for the metastable states of the Ca$^+$, Sr$^+$ and Ba$^+$ alkaline earth-metal ions are estimated. We also give the scalar quadrupole polarizabilities of the ground and metastable states of these ions to compare our results with the previously available theoretical and experimental results. Reasonably good agreement between our calculations with the previous values of scalar quadrupole polarizabilities demonstrate their correctness. The reported scalar and tensor quadrupole polarizabilit…
Laser-induced fluorescence (LIF) performed on metastable ions is frequently used to probe the dynamics of ground-state ion motions in many laboratory plasmas. However, these measurements place restrictions on the metastable ion lifetime. Metastable states are produced from direct ionization of neutral atoms as well as ions in other electronic states, of which the former will only faithfully represent processes that act on the ion dynamics in a time shorter than the metastable lifetime. We present here the first experimental study of this type of systematic effect using wave-particle interactio…
On-line Excited-State Laser Spectroscopy of Trapped Short-Lived Ra$^+$ Ions
作为一个单一的捕获Ra $^+$离子的原子宇称破坏实验的重要一步，激光光谱实验进行了与在线产生的短寿命$^{212,213,214}$ Ra $^+$离子。测量了$^{213}$ Ra $^+$中$6\,^2$ D $_{3/2}$ \，-\，$7\,^2$ P $_{1/2}$和$6\,^2$ D $_{3/2}$ \，-\，$7\,^2$ P $_{3/2}$跃迁的同位素位移和$7\,^2$ S $_{1/2}$和$6\,^2$ D $_{3/2}$态的超精细结构常数。这些值为所需的原子理论提供了基准。通过光学搁置测量亚稳态$6\,^2$ D $_{5/2}$状态的寿命的下限$232(4)$ ms。
The Cold-target recoil-ion momentum spectroscopy (COLTRIMS) has been employed to study the single-electron capture processes in collisions of N3+ ions with He atoms at an impact energy of 30 keV. The relative differential cross sections for the capture to different orbitals of N3+ ions are obtained and are compared with other experiments at low energy. The predictions of the molecular Columbic barrier model have been made. From the longitudinal momentum spectrum of recoil ions, the different electronic configuration was identified and the metastable projectile ions were distinguished. The sing…
Engineering magnetically insensitive qubits in metastable electronic D-states of trapped ions
IonQ, Inc.（IonQ公司）；Joint Quantum Institute and Department of Physics, University of Maryland（马里兰大学联合量子研究所与物理系）；Infleqtion, Inc.（Infleqtion公司）；National Institute of Standards and Technology（美国国家标准与技术研究院）；Keysight Technologies（是德科技）；Duke Quantum Center, Department of Electrical and Computer Engineering and Department of Physics, Duke University（杜克大学电气与计算机工程系、物理系及杜克量子中心）
We report measurements of excitation functions for the O$^{+}-$N$_{2}$ process with the incident beam of $1-10$ keV O$^{+}$ in the ground O$^{+}(^{4}S)$ and metastable O$^{+}(^{2}D)$ and O$^{+}(^{2}P)$ states. The measurements are performed with the sufficiently high energy resolution of 0.001 eV, which allows to distinguish the excitation channels. The excitation cross section induced by incident ions in the metastable state O$^{+}(^{2}P)$ is much larger than that for the ground O$^{+}(^{4}S)$. The excitation cross section of N$_{2}^{+}$ ion for (0,0), (0,1) and (1,2) bands system is measured…
Possible evidence for the production of Ar$_2^{*-}$ metastable negative molecular ions in gaseous argon of two-phase detectors for dark matter searches
Extensive information, such as ion temperature and wave-particle interactions, can be obtained by direct measurement of ion distribution functions using laser-induced fluorescence (LIF). This nonintrusive plasma diagnostic provides an important window into the ion motions in phase-space. Previous simulation results suggest that LIF measurements, which are performed on metastable ions produced directly from neutral gas particles and also from ions in other electronic states, place restrictions on the metastable lifetime. In the case where metastable population is produced from direct ionization…
Absolute photoionization cross sections for the Rb$^{2+}$ ion were recently measured at high resolution over the energy range 37.31 eV -- 44.08~eV, with autoionizing Rydberg resonance series identified, using the photon-ion merged-beam setup at the Advanced Light Source (\textsc{als}) in Berkeley {(Macaluso D A et. al. J. Phys. B: At. Mol. Opt. Phys. {\bf 49} (2016) 235002; {\bf 50} (2017) 119501)}. Detailed photon-energy scans taken at 13.5 $\pm$ 2.5 meV bandwidth illustrated multiple Rydberg resonance series associated with the ground and metastable states. Here we present theoretical cross …
State-resolved valence shell photoionization of Be-like ions: experiment and theory
高分辨率的光电离实验进行了使用光束的Be类C $^{2+}$，N $^{3+}$，和O $^{4+}$离子与大致相等的人口的$^1$ S基态和$^3$ P $^o$歧管的亚稳成分。实验的能量标度进行校准，根据光子能量的不确定性为1至10毫电子伏。达到了超过20，000的分辨力，允许分离来自各个亚稳态$^3$ P $^o_0$、$^3$ P $^o_1$和$^3$ P $^o_2$状态的贡献。测量的数据与半相对论Breit-Pauli R矩阵相比，
The unstable radium nucleus is appealing for probing new physics due to its high mass, octupole deformation and energy level structure. Ion traps, with long hold times and low particle numbers, are excellent for work with radioactive species, such as radium and radium-based molecular ions, where low activity, and hence low total numbers, is desirable. We address the challenges associated with the lack of stable isotopes in a tabletop experiment with a low-activity ($\sim 10 \ μ\mathrm{Ci}$) source where we laser-cool trapped radium ions. With a laser-cooled radium ion we measured the $7p\ ^2P_…
Experimental and theoretical cross sections are reported for single-photon single ionization of W$^{5+}$ ions. Absolute measurements were conducted employing the photon-ion merged-beams technique. Detailed photon-energy scans were performed at (67$\pm$10)~meV resolution in the 20 -- 160 eV range. In contrast to photoionization of tungsten ions in lower charge states, the cross section is dominated by narrow, densely-spaced resonances. Theoretical results were obtained from a Dirac-Coulomb R-matrix approach employing a basis set of 457 levels providing cross sections for photoionization of W$^{…
Michel Barat passed away in November 2018 at the age of 80 after a rich career in atomic and molecular collisions. He had participated actively in formalizing to the electron promotion model, contributed to low energy reactive collisions at the frontier of chemistry. He investigated electron capture mechanisms by highly charged ions, switched to collision induced cluster dissociation and finally to UV laser excitation induced fragmentation mechanisms of biological molecules. During this highly active time he created a lab, organized ICPEAC and participated actively in the administration of res…
Relativistic atomic structure calculations are carried out in alkaline-earth-metal ions using a semiempirical-core-potential approach. The systems are partitioned into frozen-core electrons and an active valence electron. The core orbitals are defined by a Dirac-Hartree-Fock calculation using the grasp2k package. The valence electron is described by a Dirac-like Hamiltonian involving a core-polarization potential to simulate the core-valence electron correlation. The associated equation is solved with the Lagrange-mesh method, which is an approximate variational approach having the form of a m…
Observation of molecular dynamics with quantum state resolution is one of the major challenges in chemical physics. Complete characterization of collision dynamics leads to the microscopic understanding and unraveling of different quantum phenomena such as scattering resonances. We present a new experimental approach for observing molecular dynamics involving neutral particles and ions that is capable in providing state-to-state mapping of the dynamics. We use Penning ionization reaction between argon and metastable helium to generate argon ion and ground state helium atom pairs at separation …
Electron attachment to SF6 and lifetimes of SF6- negative ions
研究了SF6分子对低能电子的俘获过程。我们的方法是基于Gauyacq和Herzenberg [J. Phys. B 17，1155（1984）]的模型，其中电子运动通过弱束缚或虚s态耦合到完全对称的振动模式。通过调整模型的两个自由参数，我们实现了对测量的电子附着截面的精确描述，并与完全对称模的振动激发截面有很好的一致性。该模型的扩展提供了一个限制的特征时间的分子内振动弛豫在高激发SF6-。通过计算SF6-的总振动谱密度，我们估算了长寿命负离子的振动费什巴赫共振宽度。我们还分析了可能的宽度分布及其对寿命测量的影响，并研究了亚稳态SF6-的非指数衰减特性。
The notion of universal quantum computation can be generalized to multi-level qudits, which offer advantages in resource usage and algorithmic efficiencies. Trapped ions, which are pristine and well-controlled quantum systems, offer an ideal platform to develop qudit-based quantum information processing. Previous work has not fully explored the practicality of implementing trapped-ion qudits accounting for known experimental error sources. Here, we describe a universal set of protocols for state preparation, single-qudit gates, a new generalization of the Mølmer-Sørensen gate for two-qudit gat…
The ion populations most frequently adopted for diagnostics in collisional plasmas are derived from the density independent, coronal approximation. In higher density, lower temperature conditions, ionisation rates are enhanced once metastable levels become populated, and recombination rates are suppressed if ions recombine into Rydberg levels. As a result, the formation temperatures of ions shift, altering the diagnostics of the plasma. To accurately model the effect of ionisation from metastable levels, new electron impact, ionisation cross sections have been calculated for oxygen, both for d…
In this work, visible and extreme ultraviolet spectra of W7+ are measured using the high-temperature superconducting electron-beam ion trap (EBIT) at the Shanghai EBIT Laboratory under extremely low-energy conditions (lower than the nominal electron-beam energy of 130 eV). The relevant atomic structure is calculated using the flexible atomic code package based on the relativistic configuration interaction method. The GRASP2K code, in the framework of the multiconfiguration Dirac-Hartree-Fock method, is employed as well for calculating the wavelength of the M1 transition in the ground configura…
State-resolved electron capture in low-energy Ar2+-Ar/N2 collisions
Northwest Normal University（西北师范大学）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）
