基于多能级速率方程的CaH分子三维磁光囚禁模型

分子激光冷却与磁光囚禁在超越标准模型的新物理与新机制探索、超冷化学与冷分子碰撞等诸多领域中有着广泛的应用前景. CaH分子的某些态之间具有高度对角化的弗兰克-康登因子,因此早在2004年就被提出作为激光冷却与磁光囚禁的候选分子之一.利用速率方程并考虑双频效应的影响,本文计算了A²Π_1/2←X²Σ⁺与B²Σ⁺←X²Σ⁺跃迁中CaH分子磁光阱内阻尼力和囚禁力的大小,分析了四频率组分和多频率组分激光设置下CaH分子磁光囚禁时的冷却和囚禁效果.结果发现,A²Π_1/2←X²Σ⁺跃迁中, CaH分子在多频率组分激光设置下可获得更大的阻尼力和囚禁力,从而有利于实现CaH分子磁光阱.以上工作不仅证明了CaH分子磁光囚禁的可行性以及为实验探索提供了必要的理论支持,同时也为超冷分子碰撞、极性冷分子BEC、基于极性冷分子的精密测量物理(如电子电偶极...     

磁光阱中冷原子的实验特性

冷原子的获得对于原子物理的研究具有重要的意义,文章综述了激光冷却与囚禁原子技术发展以来对磁光阱中中性冷原子特性的研究进展,包括冷原子对光子的吸收与散射,冷原子之间的吸引与排斥导致的超冷碰撞与长程分子状态,朱子的非线性特性等。     

冷镱原子精密光谱的研究进展

文章简要介绍了冷原子精密光谱研究方面的重要进展,报道了作者所在课题组近年来在镱原子的激光冷却与囚禁、光晶格中冷镱原子的量子操控、冷镱原子钟跃迁谱的精密测量、冷镱原子光钟的闭环锁定和频率稳定性测量等方面所取得的最新研究结果,最后对光学原子钟的发展进行了展望。     

冷原子的双阱微磁表面囚禁

提出了两种新颖的采用载流导线的双阱微磁表面囚禁方案(即双U形与双Z形导线囚禁)。通过改变囚禁方案中直导线中的电流方向，即可将双U形导线囚禁改变为双Z形导线囚禁；如果逐渐减小直导线中的电流大小，即可将一个双阱微磁囚禁连续地合并为一个单阱微磁囚禁，反之亦然。详细计算和分析了上述两种载流导线囚禁方案的磁场及其梯度的空间分布。研究发现在导线中通以较小的电流，即可在导线表面附近产生很大的磁场梯度及其曲率。例如当电流为O．2A时，其磁场梯度和曲率可分别达到0．2T／cm和10T／cm2以上。由于双U形导线囚禁中存在磁场零点，而双Z形导线囚禁中仅存在磁场最小值，所以双U形导线囚禁仅适用于制备双样品磁光囚禁(MOT)或研究中性原子的冷碰撞，而双Z形导线囚禁除了可用于研究原子的冷碰撞之外，还可以用于制备双样品玻色-爱因斯坦凝聚(BEC)或实验研究双阱玻色-爱因斯坦凝聚的性质等。     

一种实现冷分子囚禁的可控制静电双阱方案

提出了采用双环形载荷导线和两透明电极系统实现冷分子静电囚禁的可控制静电双阱的新方案,计算了带电圆导线和带电板所产生的静电场分布,从几个方面分析了这个囚禁方案的优点. 提出了一种有效的冷分子装载方法,并研究了双阱到单阱的演化过程. 研究表明,该可控制静电双阱方案不仅方便装载与操控弱场搜寻态的极性冷分子,而且在分子物质波的干涉、纠缠、冷碰撞,甚至进行双阱分子BEC研究等分子光学领域中有着广阔的应用前景. 关键词： 极性冷分子 静电囚禁 可控制静电双阱 分子光学     

在芯片表面囚禁冷极性分子的多功能静电阱EI北大核心CSCD

提出了一种用一对金属平板电容器和4根半埋入绝缘介质的杆电极组成的用于囚禁处于弱场搜寻态的冷极性分子的静电表面阱方案。用有限元软件计算了单阱囚禁时的空间电场分布,发现芯片表面上方2.2 mm左右形成了一个三维封闭的静电阱。选用重氨(ND_3)分子作为测试分子,用经典的蒙特卡罗方法模拟了ND_3分子被装载和囚禁的动力学过程。模拟结果表明,当ND_3分子束中心速度为13m/s、装载时刻为0.576ms时,最大装载效率可达53%,被囚禁的冷极性分子的温度约为35mK;如果继续增大平板电极的电压,则原先的单阱将对称分裂为两个阱,两个阱中的分子数目比为1…1;通过改变中间两个杆电极的电压,可实现非对称分裂,以此来调节两阱中囚禁分子数目比;可实现在0%~100%范围内左阱和右阱的分子数目占总分子数目的比例的调节。该方案为进一步研究三维囚禁型冷极性分子静电表面干涉仪打下基础,对于精密测量和研究物质波干涉有着重要的意义。     

在芯片表面囚禁冷极性分子的多功能静电阱

提出了一种用一对金属平板电容器和4根半埋入绝缘介质的杆电极组成的用于囚禁处于弱场搜寻态的冷极性分子的静电表面阱方案。用有限元软件计算了单阱囚禁时的空间电场分布,发现芯片表面上方2.2 mm左右形成了一个三维封闭的静电阱。选用重氨(ND_3)分子作为测试分子,用经典的蒙特卡罗方法模拟了ND_3分子被装载和囚禁的动力学过程。模拟结果表明,当ND_3分子束中心速度为13m/s、装载时刻为0.576ms时,最大装载效率可达53%,被囚禁的冷极性分子的温度约为35mK;如果继续增大平板电极的电压,则原先的单阱将对称分裂为两个阱,两个阱中的分子数目比为1…1;通过改变中间两个杆电极的电压,可实现非对称分裂,以此来调节两阱中囚禁分子数目比;可实现在0%~100%范围内左阱和右阱的分子数目占总分子数目的比例的调节。该方案为进一步研究三维囚禁型冷极性分子静电表面干涉仪打下基础,对于精密测量和研究物质波干涉有着重要的意义。     

高准确度的钙离子光频标

近年来,冷原子技术和激光技术促进了高精度光频标的发展,有望在建立时间基准、推动基础研究和满足国家需求等方面发挥重要的作用.本文介绍了中国科学院武汉物理与数学研究所近年来在高准确度钙离子(~(40)Ca~+)光频标研究方面的进展:采用新的ULE腔系统,实现了729 nm钟跃迁激光器1—100 s的频率稳定度均优于2×10~(-15),通过对外场和环境效应的控制及克服,特别是囚禁离子运动效应的抑制,获得单个钙离子光频标的不确定度优于5.5×10~(-17);通过两台光频标的比对,测得20000 s的稳定度也进入10~(-17)量级;基于高精度钙离子光频标平台,进行了相关精密测量的工作,包括:基于全球定位系统的超高精度远程光频绝对值测量方案,第二次测量了钙离子的光频跃迁绝对值,该测量结果再次被国际时间频率咨询委员会采纳,更新了钙离子的频率推荐值;精确测量了钙离子的钟跃迁魔幻波长,由此提出新型的全光囚禁离子光频标的方法;精密测量了钙离子的亚稳态寿命等参数.以上工作推动了基于冷原子的精密测量工作.     

第四讲 冷分子的导引、分束、反射、聚焦与囚禁等操控技术

近年来,随着冷分子制备技术的不断发展和冷分子温度的不断降低,冷分子操控技术取得了快速发展,并日趋成熟。文章首先介绍了冷分子导引、分束、反射与聚焦等操控的技术方案、实验结果及其最新研究进展。接着重点介绍冷分子静电囚禁、磁囚禁和光学囚禁的各种方案、实验结果及最新进展。最后就冷分子操控技术的应用进行了简单的总结与展望。     

Molecular Axis Orientation in Charge Transfer Reactions Determined with a Reaction Microscope

基于在近代物理研究所建成的反应显微成像谱仪,实验研究了在分子离子与He原子碰撞中的电荷交换反应机制. 通过运动学完全测量实验充分展示了此碰撞体系的特征. 由于采用了符合测量技术和数据列表模式记录数据,因此实验记录了每个事件中因分子离子解离而产生的碎片的三维动量信息. 在离线数据分析和处理中,根据解离碎片的动量可以确定每个事件中的H₂⁺分子离子的分子轴取向. 在近轴反冲核近似下,可以认为实验测量得到的分子轴取向就是电荷交换碰撞时刻分子轴的取向. 实验中分子轴取向的     

Molecular collisions: From near-cold to ultra-cold

In the past two decades, the revolutionary technologies of creating cold and ultracold molecules have provided cutting-edge experiments for studying the fundamental phenomena of collision physics. To a large degree, the recent explosion of interest in the molecular collisions has been sparked by dramatic progress of experimental capabilities and theoretical methods, which permit molecular collisions to be explored deep in the quantum mechanical limit. Tremendous experimental advances in the field have already been achieved, and the authors, from an experimental perspective, provide a review of these studies for exploring the nature of molecular collisions occurring at temperatures ranging from the Kelvin to the nanoKelvin regime, as well as for applications of producing ultracold molecules.     

一种可控的Ioffe型冷分子表面微电阱

囚禁于阱中的粒子(原子或分子)可获得更长的相互作用时间,因而在精密测量中可获得更高的分辨率.阱中的粒子与外界隔离,从而可以被冷却到更低的温度.因此原子(或分子)阱已广泛应用到许多研究领域.然而中心电场强度为零的势阱会导致粒子发生非绝热跃迁,这是原子或分子损失的主要来源.该损失曾是制备原子玻色-爱因斯坦凝聚的最后一道障碍.本文提出了一种可控的Ioffe型表面微电阱,其电场强度处处不为零,可有效避免分子的非绝热损失.另外,通过调节电压等参数,势阱中心电场强度以及势阱中心距芯片表面的高度可以在较大范围内调节,例如在本文参数下,势阱中心电场强度可在0.15—5.5 kV/cm变化,势阱中心高度可在6.0—17.0μm变化.本文通过有限元软件计算了芯片表面微电阱的电场分布,并用Monte Carlo模拟验证了该方案的可行性.该表面微电阱不仅可用于分子芯片的集成,而且可用于表面量子简并气体的制备.为精密测量、量子计算、表面冷碰撞和冷化学等领域提供了一个平台.     

Novel electrostatic trap for cold polar molecules

We propose a novel scheme in which cold polar molecules are trapped by an electrostatic field generated by the combination of a pair of parallel transparent electrodes (i.e., two infinite transparent plates) and a ring electrode (i.e., a ring wire). The spatial distributions of the electrostatic fields from the above charged wire and the charged plates and the corresponding Stark potentials for cold CO molecules are calculated; the dependences of the trap centre position on the geometric parameters of the electrode are analysed. We also discuss the loading process of cold molecules from a cold molecular beam into our trap. This study shows that the proposed scheme is not only simple and convenient to trap, manipulate and control cold polar molecules in weak-field-seeking states, but also provides an opportunity to study cold collisions and collective quantum effects in a variety of cold molecular systems, etc.     

Spectroscopic properties of the molecular ions BeX+ (X=Na,K, Rb): forming cold molecular ions from an ion–atom mixture by stimulated Raman adiabatic process

In this theoretical work, we calculate potential energy curves, spectroscopic parameters and transition dipole moments of molecular ions BeX⁺ (X=Na, K, Rb) composed of alkaline ion Be and alkali atom X with a quantum chemistry approach based on the pseudopotential model, Gaussian basis sets, effective core polarisation potentials and full configuration interaction. We study in detail collisions of the alkaline ion and alkali atom in quantum regime. Besides, we study the possibility of the formation of molecular ions from the ion–atom colliding systems by stimulated Raman adiabatic process and discuss the parameters regime under which the population transfer is feasible. Our results are important for ion–atom cold collisions and experimental realisation of cold molecular ion formation.     

Combination of multiple tools for surface manipulation of polar molecules

A scheme of surface manipulation and control of polar molecules is proposed, which combines three tools of electrostatic velocity filtering, bunching, and storing. In the scheme, a slow molecular beam is produced from an effusive beam by surface velocity filtering. Then the velocity spread of the slow molecular beam is compressed by a buncher consisting of a series of electrodes. Following that the molecular beam with a narrow velocity spread is stored in a storage ring. Using ND_3 molecule as a tester, the feasibility of our scheme is analyzed theoretically and verified via numerical simulations that cover all three manipulation processes. The results show that cold molecular samples can be prepared from a thermal gas reservoir and stored in the storage ring with more than 10 round trips. Our combined scheme facilitates the production and manipulation of polar molecules, offering new opportunities for basic research and intriguing applications such as quantum information science and cold collisions.     

Large effects of electric fields on atom-molecule collisions at millikelvin temperatures

Controlling interactions between cold molecules using external fields can elucidate the role of quantum mechanics in molecular collisions. We create a new experimental platform in which ultracold rubidium atoms and cold ammonia molecules are separately trapped by magnetic and electric fields and then combined to study collisions. We observe inelastic processes that are faster than expected from earlier field-free calculations. We use quantum scattering calculations to show that electric fields can have a major effect on collision outcomes, even in the absence of dipole-dipole interactions.     

Spontaneous evolution of rydberg atoms into an ultracold plasma

We have observed the spontaneous evolution of a dense sample of Rydberg atoms into an ultracold plasma, in spite of the fact that each of the atoms may initially be bound by up to 100 cm(-1). When the atoms are initially bound by 70 cm(-1), this evolution occurs when most of the atoms are translationally cold, <1 mK, but a small fraction, approximately 1%, is at room temperature. Ionizing collisions between hot and cold Rydberg atoms and blackbody photoionization produce an essentially stationary cloud of cold ions, which traps electrons produced later. The trapped electrons rapidly collisionally ionize the remaining cold Rydberg atoms to form a cold plasma.     

One and Two Photon Excitation of Radiofrequency Trapped Ca+

射频囚禁离子被广泛应用于量子信息和冷分子制备. 对于从单个离子到10^6个离子不等的样品,这些原子的内能和外能可以被控制到非常高的精度. 重点讨论了利用射频囚禁的Ca+来作为频率计量的标准方法.     

Sympathetic cooling of molecular ions in selected rotational and vibrational states produced by threshold photoionization

We present a new method for the generation of rotationally and vibrationally state-selected, translationally cold molecular ions in ion traps. Our technique is based on the state-selective threshold photoionization of neutral molecules followed by sympathetic cooling of the resulting ions with laser-cooled calcium ions. Using N?(+) ions as a test system, we achieve >90% selectivity in the preparation of the ground rovibrational level and state lifetimes on the order of 15 minutes limited by collisions with background-gas molecules. The technique can be employed to produce a wide range of apolar and polar molecular ions in the ground and excited rovibrational states. Our approach opens up new perspectives for cold quantum-controlled ion-molecule-collision studies, frequency-metrology experiments with state-selected molecular ions and molecular-ion qubits.     

Loss estimation of electrostatically trapped ND3 molecules

Losses of electrostatically trapped molecules are caused by the Majorana transition or the inelastic collisions between trapped molecules. The loss rate of electrostatically trapped ND₃ molecules in the (J=1,K=1,M=1, A) state was estimated: ND₃ molecules in this state have actually been trapped. When trapping cold molecules, using ¹⁵ND₃ molecules (fermion) with a minimum electric field higher than 10 kV/cm yields high stability.