单离子囚禁和冷却的研究进展

激光冷却和离子囚禁技术的结合为表光谱和量子力学实验提供了非常有用的工具。文章主要介绍了单个囚禁冷却离子的研究动态和发展方向。     

相干时间超过10 min的单离子量子比特

能够长时间储存量子信息的量子存储设备是实现大规模量子计算和量子通信的基本要素.与其他量子计算平台相比,囚禁离子系统的优势之一在于具有很长的相干时间.此前,基于囚禁离子的单量子比特相干时间不到1 min.研究发现,在囚禁离子系统中,限制量子比特相干时间的主要因素是运动能级加热和环境噪声,其中后者包含环境磁场涨落和微波相位噪声.在同时囚禁171Yb+离子和138Ba+离子的混合囚禁系统中,通过实施协同冷却和动力学解耦,可以实现相干时间超过10 min的单离子量子比特.这一技术有望用于实现量子密码学和搭建混合量子计算平台.     

全光学冷却与囚禁133Cs原子玻色-爱因斯坦凝聚的可能性

综述了近年来有关蒸发冷却¹³³Cs原子样品的实验进展,分析了磁囚禁¹³³Cs原子玻色爱因斯坦凝聚(BEC)的困难,并在此基础上提出了一个全光型冷却与囚禁¹³³Cs原子BEC的新方案.该方案主要由一个来自半导体激光(λ=0852μm)的倒金字塔形中空光束重力光学囚禁(pyramidal-hollow-beam gravito-optical trap,缩写为PHB GOT)和一个来自Ar⁺激光(λ=05013μm)的圆锥形中空光束重力光学囚禁(conical-hollow-beam gravito-optical trap,缩写为CHB GOT)组成.在PHB GOT中,冷原子经历了一个有效的中空光束感应的Sisyphus冷却(也即强度梯度冷却)和抽运光感应的几何冷却,原子温度将被从磁光囚禁(MOT)温度(约为60μK)冷却至几个光子反冲极限(约为2μK);而在Ar⁺中空光束囚禁(CHB GOT)中,冷原子将被Raman冷却或速度选择相干粒子数囚禁技术(velocity-selection coherent population trap,缩写为VSCPT)进一步冷却至光子反冲极限以下,并被激光频率高于原子共振频率的(也即蓝失谐的)covering光束压缩.我们就PHB冷却的动力学过程进行了Monte-Carlo模拟,并计算了Ar⁺中空光束囚禁¹³³Cs原子的光学势.研究结果表明,实现一个全光学冷却与囚禁的¹³³Cs原子BEC是可能的 关键词： 倒金字塔型中空光束重力光学囚禁 强度梯度冷却 氩离子中空光束囚禁 喇曼冷却 铯原子BEC     

可扩展的用于量子信息处理的刻槽平面离子芯片设计

研究设计了一个有效的可扩展的二维刻槽离子芯片。为了减少激光在离子芯片表面的散射,使被囚禁离子更加稳定,并使激光容易控制和探测成行的被囚禁离子,在每两个平行的射频电极中间刻槽使冷却光和探测光路径可穿过芯片。把控制离子运动的直流电极跟射频电极分开,减轻了不同电压对被囚禁离子的干扰,改进了对离子的控制。用有限元分析的方法对芯片表面上方的电势分布做了计算模拟。模拟结果表明,在这种新型的刻槽可扩展芯片上可以生成一个可扩展的离子阱阵列。这种结构提供了一个新颖的刻槽二维平面离子芯片,被囚禁其上的线形离子阵列可用来进行大型的量子信息处理。     

HIRFL-CSR主环电子冷却模拟计算

以¹⁶O⁸⁺为例,用电子冷却模拟程序计算了冷却时间随离子能量、初始发射度、初始动量分散、离子流强以及离子电荷态的变化规律,研究了储存环在冷却段的β函数和色散函数对冷却时间的影响.     

基于三角形衍射光栅的原子冷却囚禁实验研究

基于三角形衍射光栅搭建的三维磁光阱实现了87Rb原子的冷却囚禁,自主完成了三角形衍射光栅的设计制备,在保证合理衍射效率及衍射圆偏度的情况下有效抑制了零级光效率,其参数满足光学粘胶平衡条件。基于该光栅搭建了一套磁光阱系统,开展原子囚禁实验。在合理的参数设置下,成功实现了原子囚禁,经测算囚禁原子数量在106量级。基于三角形衍射光栅的原子冷却囚禁实验的成功,对于三维磁光阱的低功耗、小型化具有参考意义,有望应用于小型化冷原子精密测量系统中。     

第三讲 化学稳定分子的激光减速、冷却及其MOT技术

文章首先介绍了分子激光减速和冷却的基本原理、技术方案及其最新进展,主要包括分子的选择、分子激光减速、分子激光冷却、电光冷却多原子分子等。接着简单介绍了分子磁光囚禁的基本原理、技术方案及其最新研究进展。最后,就分子“激光减速、冷却与磁光囚禁”的研究进行了简单的总结与展望。     

Paul阱中离子云囚禁时间的分析

结合缓冲气体Ｈｅ对囚禁离子云Ｎ＾＋２的冷却实验结果，给出了在综合考虑射频加热和缓冲气体冷却效应情形下，阱中囚禁离子数随时间变化的理论模型。讨论了Ｐａｕｌ阱中的加热数，γ，离子云温度Ｔ，随机为力涨落Ｄ等参数对囚禁时间的影响。     

极性分子的激光冷却及囚禁技术

分子由于其不同于原子的特殊性质,在原子、分子和光物理研究中有其独特的地位.冷分子研究已经开展了二三十年,取得了很多重大的进展.但是以斯塔克减速器为代表的传统冷却方案遇到瓶颈,很难进一步提高分子的相空间密度.将原子中成熟的激光冷却技术拓展到极性分子中是本领域近年来的重大突破,使得冷却和囚禁分子的范围得以大大扩展,分子的相空间密度也得以提高.本文对国内外激光冷却极性分子的最新成果进行综述,并以BaF分子为例介绍激光冷却极性分子的相关理论和技术,包括分子能级结构分析及精密光谱测量,采用缓冲气体冷却进行态制备和预冷却,以及通过冷分子束研究激光与BaF分子间的相互作用.这些为后续开展激光冷却与囚禁实验研究奠定了基础,也为开展其他新的分子冷却实验提供了参考.     

激光冷却与囚禁原子技术及应用

综述了激光冷却与囚禁中性原子应用研究方面的新进展，着重从物理图像上介绍了这些应用的机理。     

能量传递制冷机制中激光制冷的最佳泵浦频率和最大制冷效率

在能量传递型激光制冷中,对于非均匀线宽比较窄的情况,引起最大制冷效率的激发光频率不随温度的变化而变化最大制冷效率与温度呈三次暴的关系。对于非均匀线宽比较宽的情况。随着温度的降低,最佳激发光频率与非均匀线形的中心频率差越来越大,并在较低的温度下迅速拉大它们间的距离。由能量传递机制所引起的荧光制冷最大效率也随着温度的降低而越来越低,并在最后趋于零。它们随温度的降低而降低的规律与实验中得到的结论相符合。     

Effect of impingement jet on the full-coverage film cooling system with double layered wall

The present study was conducted to evaluate the total cooling effectiveness in combined full-coverage film cooling and impingement jet using an infrared thermographic technique. The effect of film cooling hole angle, blowing ratio, and height to diameter ratio between the film cooling and impingement jet plates was discussed. The total cooling effectiveness increased as impingement jet cooling was added. The angled film cooling holes had approximately 4.6% higher total cooling effectiveness than the normal film cooling holes. The total cooling effectiveness was almost constant regardless of height to diameter ratio, but enhanced as the blowing ratio was increased.     

Enhanced Laser Cooling of Rare-Earth-Ion-Doped Glass Containing Nanometer-Sized Metallic Particles

The enhanced laser cooling performance ofrare-earth-ions-doped glasses containing small particles is predicted. Thisis achieved by the enhancement of local field around rare earth ions, owingto the surface plasmon resonance of small metallic particles. The role ofenergy transfer between ions and the particle is theoretical discussed.Depending on the particle size and the ion emission quantum efficiency, theenhancement of the absorption and the fluorescence is predicted. Moreover,taking Yb³⁺-doped ZBLAN as example, the cooling power and heat-lightconverting efficiency are calculated. It is finally concluded that theabsorption and the fluorescence are greatly enhanced in these compositematerials, the cooling power is increased compared to the bulk material.     

HIRFL-CSRm冷却束流寿命

实验研究了HIRFL-CSRm中电子冷却装置对C6+,Ar15+两种束流寿命的影响。首先,通过对比实验的测量确定电子冷却可以有效提高束流寿命;其次,探究了电子冷却装置中的各项参数（主要是电子束密度分布、流强、能量、绝热展开因子）是如何影响束流寿命的,通过改变电子束参数,测量束流寿命的变化趋势和规律,并且结合电子冷却相关理论对实验结果给予解释,最终通过实验优化和确定最佳的冷却装置参数,使束流在HIRFL-CSRm上获得了较高的寿命,从而提高HIRFL-CSRm束流累积过程中的流强增益。     

The HITRAP project at GSI: trapping and cooling of highly-charged ions in a Penning trap

A decelerator will be installed at GSI in order to provide and study heavy nuclei without or with only few electrons at very low energies or even at rest. Highly-charged ions will be produced by stripping at relativistic energies. After electron cooling and deceleration in the Experimental Storage Ring (ESR) the ions are ejected out of the storage ring at 4 MeV/u and further decelerated in a combination of linear accelerator structures operated in reverse. Finally, they are injected into a Penning trap where the ions are cooled to 4 K by electron cooling in combination with resistive cooling. From here, the ions can be transferred in a quasi DC or in a pulsed mode to different experimental setups. This article describes the technical concepts of this project focused on the Penning trap.      

A cooler ion trap for the TITAN on-line trapping facility at TRIUMF

We present simulations of electron and proton cooling of highly charged ions in a Penning trap, including the potentially detrimental effects of radiative, dielectronic, and three-body recombination in electron cooling. We show a preliminary design for a cooler trap accommodating both electron and proton cooling, which will be a component of the TITAN ion-trap facility under construction at TRIUMF for precision mass measurements of short-lived radioactive nuclei.      

改善局部难冷区域的一种导叶层板端壁

受二次流的影响,气膜冷却端壁表面存在大量难冷区域。紧凑型层板结构可以实现端壁的双侧冷却,从而缩小难冷面积。本文通过改变气膜孔布局,设计了一种可以有效改善局部难冷区域的层板冷却端壁。在主冷流温比1.5下,测量了端壁表面的温降特性和综合冷却效率分布,通过与均匀气膜布局的层板端壁相比较,发现:采用改进后的层板结构,可以显著降低端壁表面温度,缩小难冷区域面积,获得更均匀的冷却效果。且压力侧根部区域与吸力面前缘区域冷却效果增幅尤甚。另外,此层板的改进优势随着质量流量比的增加变得更明显。     

Effective sideband cooling in an ytterbium optical lattice clock

Sideband cooling is a key technique for improving the performance of optical atomic clocks by preparing cold atoms and single ions into the ground vibrational state. In this work, we demonstrate detailed experimental research on pulsed Raman sideband cooling in a $^{171}$Yb optical lattice clock. A sequence comprised of interleaved 578 nm cooling pulses resonant on the 1st-order red sideband and 1388 nm repumping pulses is carried out to transfer atoms into the motional ground state. We successfully decrease the axial temperature of atoms in the lattice from 6.5 μK to less than 0.8 μK in the trap depth of 24 μK, corresponding to an average axial motional quantum number $\langle n_z\rangle<0.03$. Rabi oscillation spectroscopy is measured to evaluate the effect of sideband cooling on inhomogeneous excitation. The maximum excitation fraction is increased from 0.8 to 0.86, indicating an enhancement in the quantum coherence of the ensemble. Our work will contribute to improving the instability and uncertainty of Yb lattice clocks.     

Enhanced cooling of a V-type three-level atom in an optical cavity

We have studied theoretically and numerically the enhanced cooling of a V-type three-level atom in a high-finesse optical cavity and shown that the cooling rate can be increased by one order of magnitude over that of a two-level atom, and the momentum amplitude tends to a stationary state much smaller than that of a two-level atom. We have further shown that the cooling rate can be significantly improved by using feedback and a time-dependent pump.     

Development of a broadband laser in the UV region

A frequency comb in the UV region with a bandwidth greater than 100 MHz is generated by successive frequency shifts of a single mode laser by an acousto-optic modulator coupled to a passive ring cavity. The obtained spectrum is particularly suitable for laser cooling when a large velocity capture range is required as in the case, for example, of ions confined in a storage ring. This revised version was published online in August 2006 with corrections to the Cover Date.