M. R. Dietrich, A. Avril, R. Bowler, N. Kurz, J. S. Salacka, G. Shu, B. B. Blinov
Individually trapped 137Ba+ in an RF Paul trap is proposed as a qubit ca ndidate, and its various benefits are compared to other ionic qubits. We report the current experimental status of using this ion for quantum computation. Fut ure plans and prospects are discussed.
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We have produced sympathetically cooled barium monohalide ions BaX$^+$ (X = F, Cl, Br) by reacting trapped, laser cooled Ba$^+$ ions with room temperature gas phase neutral halogen-containing molecules. Reaction rates for two of these (SF$_6$ and CH$_3$Cl) have been measured and are in agreement with classical models. BaX$^+$ ions are promising candidates for cooling to the rovibrational ground state, and our method presents a straightforward way to produce these polar molecular ions.
We study sympathetic cooling of the radial ion motion in a linear RF trap in mixed barium-ytterbium chains. Barium ions are Doppler-cooled, while ytterbium ions are cooled through their interaction with cold barium ions. We estimate the efficiency of sympathetic cooling by measuring the average occupation quantum numbers, and thus the temperature, of all radial normal modes of motion in the ion chain. The full set of orderings in a chain of two barium and two ytterbium ions have been probed, and we show that the average thermal occupation numbers for all chain configurations strongly depend on…
We have developed a vacuum chamber and control system for rapid testing of microfabricated surface ion traps. Our system is modular in design and is based on an in-vacuum printed circuit board with integrated filters. We have used this system to successfully trap and cool barium ions and have achieved ion 'dark' lifetimes of 31.6 s +- 3.4 s with controlled shuttling of ions. We provide a detailed description of the ion trap system including the in-vacuum materials used, control electronics and neutral atom source. We discuss the challenges presented in achieving a system which can work reliabl…
A version of the method of accurate calculations for few valence-electron atoms which combines linearized single-double coupled cluster method with the configuration interaction technique is presented. The use of the method is illustrated by calculations of the energy levels for Ba, Ba$^+$, Lu, Lu$^+$ and Lu$^{2+}$. Good agreement with experiment is demonstrated and comparison with previous version of the method (Safronova {\em et al}, PRA {\bf 80}, 012516 (2009)) is made.
Accurate values of electric dipole (E1) amplitudes along with their uncertainties for a number of transitions among low-lying states of Mg$^+$, Ca$^+$, Sr$^+$, and Ba$^+$ are listed by carrying out calculations using a relativistic all-order many-body method. By combining experimental wavelengths with these amplitudes, we quote transition probabilities, oscillator strengths and lifetimes of many short-lived excited states of the above ions. The uncertainties in these radiative properties are also quoted. We also give electric quadrupole (E2) and magnetic dipole (M1) amplitudes of the metastabl…
Charge-state dynamics of barium ions in high-pressure xenon and its implications for Barium-Tagging in $0νββ$ searches
该研究探究高压氙中Ba²⁺的电荷态动力学，发现中性氙辅助的三体复合可将Ba²⁺转为Ba⁺，为NEXT实验的BaTa技术设计提供了关键依据。
Increase of barium ion-trap lifetime via photodissociation
研究发现，钡离子在保罗陷阱中的寿命受限于与残留背景气体的化学反应，通过光解离可恢复离子并延长有效陷阱寿命，实验在室温下使寿命从6小时提升至2天。
Light-assisted reactive collisions between laser-cooled Ba+ ions and Rb atoms were studied in an ion-atom hybrid trap. The reaction rate was found to strongly depend on the electronic state of the reaction partners with the largest rate constant (7(2) x 10^-11 cm^3 s^-1) obtained for the excited Ba+(6s)+Rb(5p) reaction channel. Similar to the previously studied Ca+ + Rb system, charge transfer and radiative association were found to be the dominant reactive processes. The generation of molecular ions by radiative association could directly be observed by their sympathetic cooling into a Coulom…
Ablation loading of barium ions into a surface electrode trap
本文研究激光烧蚀离子装载进入不同尺寸表面电极阱，通过解析模型预测装载概率，并在730微米和50微米离子-电极距离的低温阱中成功装载钡离子，验证了模型，为限量同位素在量子信息处理中的应用提供指导。
Fast programmable entanglement of Barium ion qubits using Rydberg states and AC-Stark shifts
本文提出利用钡离子里德伯态和1310 nm电信波段交流斯塔克位移实现快速可编程纠缠，通过双光子激发和光强调制实现亚微秒离子对纠缠门及独立寻址。
Translational cooling and storage of protonated proteins in an ion trap at subkelvin temperatures
气相多电荷蛋白质已被同情地冷却到低于1 K的平移温度的库仑相互作用与激光冷却的钡离子在线性离子阱。在一种情况下，53个细胞色素c分子（质量约12390 amu，电荷+17 e）的系综被约160个激光冷却的钡离子冷却到低于0.75 K。已经观察到超过20分钟的储存时间，并且可以很容易地延长到超过一个小时。该技术适用于各种复杂分子。
Photoionization and Photoelectric Loading of Barium Ion Traps
简单而有效的技术，用于加载钡离子到线性保罗陷阱证明。中性钡的两步光电离是使用一个弱的相互组合线（6s2 1S0 <->6s6p 3P1，791 nm），然后通过使用氮气体激光器（337 nm）的电离阈值以上的激发。同位素选择性是通过使用近多普勒自由几何激发的三重态6s6p 3P1状态。此外，我们报告了一个特别简单和有效的陷阱加载技术，采用昂贵的UV环氧固化灯产生光电子。
We report on progress towards implementing mixed ion species quantum information processing for a scalable ion trap architecture. Mixed species chains may help solve several problems with scaling ion trap quantum computation to large numbers of qubits. Initial temperature measurements of linear Coulomb crystals containing barium and ytterbium ions indicate that the mass difference does not significantly impede cooling at low ion numbers. Average motional occupation numbers are estimated to be $\bar{n} \approx 130$ quanta per mode for chains with small numbers of ions, which is within a factor …
Theoretical characterisation of the barium II and radium II ions
本文采用含 Breit 和 QED 修正的全阶关联势方法，高精度计算 Ra+ 与 Ba+ 的跃迁矩阵元、寿命、极化率等，并提取 E2 矩阵元及核磁化分布参数。
Background reduction in $^{136}$Xe double beta decay experiments through direct barium ion detection
本研究提出一种仅依赖钡离子固有能级的新型探测方案，用于$^{136}$Xe双β衰变实验的钡离子标记，无需额外添加剂，简化装置并提升实验灵敏度，助力解决中微子物理关键问题。
Sympathetic cooling of trapped ions through collisions with neutral buffer gases is critical to a variety of modern scientific fields, including fundamental chemistry, mass spectrometry, nuclear and particle physics, and atomic and molecular physics. Despite its widespread use over four decades, there remain open questions regarding its fundamental limitations. To probe these limits, here we examine the steady-state evolution of up to ten barium ions immersed in a gas of three-million laser-cooled calcium atoms. We observe and explain the emergence of nonequilibrium behavior as evidenced by bi…
We study a method for mass-selective removal of ions from a Paul trap by parametric excitation. This can be achieved by applying an oscillating electric quadrupole field at twice the secular frequency $ω_{\text{sec}}$ using pairs of opposing electrodes. While excitation near the resonance with the frequency $ω_{\text{sec}}$ only leads to a linear increase of the amplitude with excitation duration, parametric excitation near $2\, ω_{\text{sec}}$ results in an exponential increase of the amplitude. This enables efficient removal of ions from the trap with modest excitation voltages and narrow ba…
We study the Doppler-cooling of radial two-dimensional (2D) Coulomb crystals of trapped barium ions in a radiofrequency trap. Ions in radial 2D crystals experience micromotion of an amplitude that increases linearly with the distance from the trap center, leading to a position-dependent frequency modulation of laser light in each ion's rest frame. We use two tones of Doppler-cooling laser light separated by approximately 100~MHz to efficiently cool distinct regions in the crystals with differing amplitudes of micromotion. This technique allows us to trap and cool more than 50 ions populating 4…
Fast photon-mediated entanglement of continuously-cooled trapped ions for quantum networking
本文提出利用真空内高数值孔径物镜收集可见光子并干涉探测，实现钡离子量子比特的高保真纠缠，同时引入镱离子协同冷却，使纠缠速率达到每秒250次，为量子网络提供连续高效的纠缠源。
A scalable narrow linewidth high power laser for barium ion optical qubit
本文验证掺铥光纤放大器可在不显著展宽种子激光线宽的情况下为钡离子光学量子比特提供高功率，并通过自外差法和离子四极光谱测得约160 Hz线宽。
The $^{133}\mathrm{Ba}^+$ ion is a promising candidate as a high-fidelity qubit, and the $^{137}\mathrm{Ba}^+$ isotope is promising as a high-fidelity qudit ($d>2$). Barium metal is very reactive, and $^{133}\mathrm{Ba}^+$ is radioactive and can only be sourced in small quantities, so the most commonly used loading method, oven heating, is less suited for barium, and is currently not possible for $^{133}\mathrm{Ba}^+$.Pulsed laser ablation solves both of these problems by utilizing compound barium sources, while also giving some distinct advantages, such as fast loading, less displaced materia…
Measurement of small photodestruction rates of cold, charged biomolecules in an ion trap
在这项工作中，我们展示了测量的光破坏率的冷冻，带电的生物分子。在超高真空条件下的离子阱中的分子离子的长期稳定存储允许测量小速率和验证速率在光破坏激光强度中是线性的。对有机化合物大黄酸（C30 H46 O 4）的单质子化分子进行测量，所述有机化合物大黄酸（C30 H46 O 4）通过使用不同强度的连续波UV激光（266 nm）解离。的分子被同情地冷却，同时捕获的激光冷却钡离子的平移温度低于150 mK。已测定的破坏速率小于0.05 s^-1，截面为（1.1 +/- 0.1）* 10^-17 cm ^2。可调谐紫外激光源的扩展将允许对各种冷复杂分子进行高分辨率解离光谱研究。
We report on single Barium ions confined in a near-infrared optical dipole trap for up to three seconds in absence of any radio-frequency fields. Additionally, the lifetime in a visible optical dipole trap is increased by two orders of magnitude as compared to the state-of-the-art using an efficient repumping method. We characterize the state-dependent potentials and measure an upper bound for the heating rate in the near-infrared trap. These findings are beneficial for entering the regime of ultracold interaction in atom-ion ensembles exploiting bichromatic optical dipole traps. Long lifetime…
Quantum computer architecture with ions in tweezer arrays
提出一种基于光学镊子阵列中离子的量子计算机架构，利用有效电偶极子间的库仑相互作用实现纠缠门，并展示了可扩展的离子镊子量子处理器路径。
Low noise quantum frequency conversion of photons from a trapped barium ion to the telecom O-band
本研究针对囚禁离子发射光子因波段限制传输距离短的问题，采用两级低噪声量子频率转换方案，将钡离子可见光光子转换为O波段电信光子，实现11%转换效率与超100信背比，推动长距离囚禁离子量子网络发展。
The electronic and motional degrees of freedom of trapped ions can be controlled and coherently coupled on the level of individual quanta. Assembling complex quantum systems ion by ion while keeping this unique level of control remains a challenging task. For many applications, linear chains of ions in conventional traps are ideally suited to address this problem. However, driven motion due to the magnetic or radio-frequency electric trapping fields sometimes limits the performance in one dimension and severely affects the extension to higher dimensional systems. Here, we report on the trappin…
We report an improved measurement of the Landé g factor of the 5D5/2 state of singly ionized barium. Measurements were performed on single Doppler-cooled 138Ba+ ions in linear Paul traps using two similar, independent apparatuses. Transitions between Zeeman sublevels of the 6S1/2 and 5D5/2 states were driven with two independent, stabilized radio-frequency synthesizers using a dedicated electrode within each ion trap chamber. State detection within each Zeeman manifold was achieved with a frequency-stabilized fiber laser operating at 1.76 microns. By calculating the ratio of the two Zeeman spl…
Trapping $\mathbf{Ba}^+$ with Seven-fold Enhanced Efficiency Utilizing an Autoionizing Resonance
针对囚禁离子量子计算机中离子装载缓慢的问题，本文比较两种 ¹³⁸Ba⁺ 同位素选择性光电离方案，证明利用自电离跃迁的两步法可将装载率提高近一个数量级，且仅需增加商用二极管激光器。
Instability Heating of Sympathetically-Cooled Ions in a Linear Paul Trap
利用计算和理论方法研究了储存在线性几何结构、射频电四极阱中离子的交感激光冷却。该模拟允许5个样品离子与35个激光冷却的原子离子相互作用，揭示了一种不稳定的加热机制，该机制可以防止低于一定临界质量的离子被同情冷却。然而，该临界质量可以通过改变捕获场参数来改变，从而允许具有非常大的质量范围的离子使用单个离子种类被同情地冷却。这种不稳定性的加热机制的理论解释，提出预测的冷却-加热边界的捕获参数空间是一条线的恒定$q_u$（离子阱稳定性系数），一个结果支持的计算结果。$q_u$的阈值取决于相互作用离子的质量。给出了这种依赖关系的函数形式。
We discuss an approach to accurate numerical computations of slowly convergent properties in two-electron atoms/ions which include the negatively charged Ps$^{-}$ ($e^{-} e^{+} e^{-}$) and H$^{-}$ ions, He atom and positively charged, helium-like ions from Li$^{+}$ to Ni$^{26+}$. All these ions are considered in their ground $1^{1}S-$state(s). The slowly convergent properties selected in this study include the electron-nulceus $\langle r^{2 k}_{eN} \rangle$ and electron-electron $\langle r^{2 k}_{ee} \rangle$ expectation values for $k$ = 2, 3, 4 and 5.
A Python Program for Computation of Transition Probabilities, Oscillator Strengths for Li-like ions
针对现有原子光谱软件依赖服务器的问题，开发了一款基于Python的程序，利用有效电荷等参数计算类锂离子的跃迁概率等光谱量，并在多种离子上验证了与NIST数据的一致性。
The direct laser cooling of neutral diatomic molecules in molecular beams suggests that trapped molecular ions can also be laser cooled. The long storage time and spatial localization of trapped molecular ions provides the opportunity for multi-step cooling strategies, but also requires a careful consideration of rare molecular transitions. We briefly summarize the requirements that a diatomic molecule must meet for laser cooling, and we identify a few potential molecular ion candidates. We then perform a detailed computational study of the candidates BH+ and AlH+, including improved ab initio…
Rapid Exchange Cooling with Trapped Ions
针对QCCD架构中协同冷却的速率瓶颈，提出交换冷却方法，利用激光冷却的冷却剂离子快速冷却计算离子，实验证明输运时间仅107微秒，移除超96%轴向能量，验证单种类处理器可行性。
A Semi-classical model is employed to theoretically study mutual neutralization in the collisions of $\mathrm{^4He^+}$ and $\mathrm{H^-}$. The model includes nine covalent states of $\mathrm{^2Σ^+}$ symmetry. Here the assumption is that only two states are interacting at a given internuclear position. The reaction is studied for collisions energies below 100 $eV$. The total mutual neutralisation cross section is computed and compared with previous results
Theoretical and Numerical studies of the positions of cold trapped ions
我们研究了线性晶体结构中的Paul阱所限制的冷离子的性质，由于其在实际量子计算中的应用，该系统具有相当大的电流兴趣。采用理论和数值计算相结合的方法，导出了离子位置的半经验公式。
Vibrational degrees of freedom in trapped-ion systems have recently been gaining attention as a quantum resource, beyond the role as a mediator for entangling quantum operations on internal degrees of freedom, because of the large available Hilbert space. The vibrational modes can be represented as quantum harmonic oscillators and thus offer a Hilbert space with infinite dimension. Here we review recent theoretical and experimental progress in the coherent manipulation of the vibrational modes, including bosonic encoding schemes in quantum information, reliable and efficient measurement techni…
The collision-energy resolved rate coefficient for dissociative recombination of HD+ ions in the vibrational ground state is measured using the photocathode electron target at the heavy-ion storage ring TSR. Rydberg resonances associated with ro-vibrational excitation of the HD+ core are scanned as a function of the electron collision energy with an instrumental broadening below 1 meV in the low-energy limit. The measurement is compared to calculations using multichannel quantum defect theory, accounting for rotational structure and interactions and considering the six lowest rotational energy…
Using discrete and continuous variable subsystems, hybrid approaches to quantum information could enable more quantum computational power for the same physical resources. Here, we propose a hybrid scheme that can be used to generate the necessary Gaussian and non-Gaussian operations for universal continuous variable quantum computing in trapped ions. This scheme utilizes two linear spin-motion interactions to generate a broad set of non-linear effective spin-motion interactions including one and two mode squeezing, beam splitter, and trisqueezing operations in trapped ion systems. We discuss p…
We propose a scalable ion trap architecture for universal quantum computation, which is composed of an array of ion traps with one ion confined in each trap. The neighboring traps are designed capable of merging into one single trap. The universal two-qubit $\sqrt{SWAP}$ gate is realized by direct collision of two neighboring ions in the merged trap, which induces an effective spin-spin interaction between two ions. We find that the collision-induced spin-spin interaction decreases with the third power of two ions' trapping distance. Even with a $200\ μm$ trapping distance between atomic ions …
Using the ab initio computed Potential Energy Surface (PES) for the electronic interaction of the MgH$^+$ ($^1Σ$) ion with the He($^1$S) atom, we calculate the relevant state-changing rotationally inelastic collision cross sections from a quantum treatment of the multichannel scattering problem. We focus on the quantum dynamics at the translationally low energies for the present partners discussed in the earlier, cold ion trap experiments (see below) which we wish to model in detail. The corresponding state-changing rates computed between the lower rotational states of the molecular ion are em…
The quantum entanglement for the two electrons in three-body atomic systems such as the helium atom, the hydrogen negative ion and the positronium negative ion are investigated by employing highly correlated Hylleraas functions to represent the ground states of such systems. As a measure of the spatial entanglement, the linear entropy of the reduced density matrix is calculated for the ground states. The required four-electron (12-dimensional) integrals are solved analytically such that they are suitable for machine computations. Results are compared with other calculations when available.
Rotational transitions induced by collisions of HD$^{+}$ ions with low energy electrons
基于多通道量子亏损理论计算HD$^+$与低能电子碰撞的转动跃迁及解离复合截面与速率系数，结果与理论和实验吻合，并提升了解离复合截面精度。
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