Enhanced optical molasses cooling for Cs atoms with largely detuned cooling lasers

We report a detailed study of the enhanced optical molasses cooling of Cs atoms,whose large hyperfine structure allows to use the largely red-detuned cooling lasers.We find that the combination of a large frequency detuning of about-110 MHz for the cooling laser and a suitable control for the powers of the cooling and repumping lasers allows to reach a cold temperature of^5.5μK.We obtain 5.1×10^7 atoms with the number density around 1×10^12 cm^-3.Our result gains a lower temperature than that got in other experiments,in which the cold Cs atoms with the temperature of^10μK have been achieved by the optical molasses cooling.

BaF radical： A promising candidate for laser cooling and magneto-optical trapping

Recently, there have been great interest and advancement in the field of laser cooling and magneto-optical trapping of molecules. The rich internal structure of molecules naturally lends themselves to extensive and exciting applications. In this paper, the radical 138Ba19F, as a promising candidate for laser cooling and magneto-optical trapping, is discussed in detail.The highly diagonal Franck-Condon factors between theX2∑＋1/2and A2∏1/2states are first confirmed with three different methods. Afterwards, with the effective Hamiltonian approach and irreducible tensor theory, the hypertine structure of theX2∑＋1/2state is calculated accurately. A scheme for laser cooling is given clearly. Besides, the Zeeman effects of the upper （ A2∏1/2）andlower（X2∑＋1/2）levels are also studied, and their respective g factors are obtained under a weak magnetic field. Its large g factor of the upper stateA2∏1/2is advantageous for magneto-optical trapping. Finally, by studying Stark effect of BaFin theX2∑＋1/2, we investigate the dependence of the internal effective electric field on the applied electric field. It is suggested that such a laser-cooled BaF is also a promising candidate for precision measurement of electron electric dipole moment.

Direct Laser Cooling Al^＋ Ion Optical Clocks

The Al^＋ ion optical clock is a very promising optical frequency standard candidate due to its extremely small black-body radiation shift. It has been successfully demonstrated with the indirect cooled, quantum-logic-based spectroscopy technique. Its accuracy is limited by second-order Doppler shift, and its stability is limited by the number of ions that can be probed in quantum logic processing. We propose a direct laser cooling scheme of AI＋ ion optical clocks where both the stability and accuracy of the clocks are greatly improved. In the proposed scheme, two Al^＋ traps are utilized. The first trap is used to trap a large number of Al^＋ ions to improve the stability of the clock laser, while the second trap is used to trap a single Al^＋ ion to provide the ultimate accuracy. Both traps are cooled with a continuous wave 167nm laser. The expected clock laser stability can reach 9.0 × 10^-17/√τ. For the second trap, in addition to 167nm laser Doppler cooling, a second stage pulsed 234nm two-photon cooling laser is utilized to further improve the accuracy of the clock laser. The total systematic uncertainty can be reduced to about 1 × 10^-18. The proposed Al^＋ ion optical clock has the potential to become the most accurate and stable optical clock.

4-7 Laser Cooling and Trapping of Rubidium Atoms

Atomic physics is developed by the realization of Magneto-Optical Trap (MOT)[1] which helps scientists achievethe miracles of Bose Einstein condensation[2], atomic frequency standard[3] and ultra-cold plasma[4]. We built arubidium MOT system and used it to cool and trap as many as 106 87Rb atoms with a density of 1010cm?3 and atemperature of 500 K.The MOT consists of three systems: the vacuum system, the laser system and the control system. The vacuumsystem is carefully designed to obtain a vacuum as high as 510?9 mbar. Rubidium atoms are evaporated intothe vacuum chamber by heating the pure rubidium metal to 40?C.

Femtosecond laser trapping dynamics of two-photon absorbing hollow-core nanoparticles

We investigate femtosecond laser trapping dynamics of two-photon absorbing hollow-core nanoparticles with different volume fractions and two-photon absorption(TPA)coefficients.Numerical simulations show that the hollow-core particles with low and high-volume fractions can easily be trapped and bounced by the tightly focused Gaussian laser pulses,respectively.Further studies show that the hollow-core particles with and without TPA can be identified,because the TPA effect enhances the radiation force,and subsequently the longitudinal force destabilizes the trap by pushing the particle away from the focal point.The results may find direct applications in particle sorting and characterizing the TPA coefficient of single nanoparticles.

Engineering steady-state entanglement for two atoms held in separate cavities through laser cooling

We propose a scheme to prepare the steady-state entanglement for two atoms, which are held in separate cavities that are coupled through a short optical fiber or optical resonator. The entangled steady-state with a high fidelity can be achieved even with a low cooperativity parameter, by making use of the driving laser fields. Such a cooling mechanism is based on a resonant laser pump of the unwanted ground states to the excited states, which finally decay to the desired steady-state.

Efficient loading of ultracold sodium atoms in an optical dipole trap from a high power fiber laser

We report on a research of the loading of ultracold sodium atoms in an optical dipole trap,generated by two beams from a high power fiber laser.The effects of optical trap light power on atomic number,temperature and phase space density are experimentally investigated.A simple theory is proposed and it is in good accordance with the experimental results of the loaded atomic numbers.In a general estimation,an optimal value for each beam with a power of 9 W from the fiber laser is achieved.Our results provide a further understanding of the loading process of optical dipole trap and laid the foundation for generation of a sodium Bose–Einstein condensation with an optical dipole trap.

Theoretical study on isotope separation of an ytterbium atomic beam by laser deflection

Isotope separation by laser deflecting an atomic beam is analyzed theoretically. Interacting with a tilted one- dimensional optical molasses, an ytterbium atomic beam is split into multi-beams with different isotopes like 172yb, Jv3yb, and J74yb. By using the numerical calculation, the dependences of the splitting angle on the molasses laser intensity and detuning are studied, and the optimal parameters for the isotope separation are also investigated. Furthermore, the isotope separation efficiency and purity are estimated. Finally a new scheme for the efficient isotope separation is proposed. These findings will give a guideline for simply obtaining pure isotopes of various elements.

Experiments on trapping ytterbium atoms in optical lattices

Experiments on trapping ytterbium atoms in various optical lattices are presented. After the two-stage cooling, first in a blue magneto-optical trap and then in a green magneto-optical trap, the ultracold 171 Yb atoms are successfully loaded into one-, two-, and three-dimensional optical lattices operating at the Stark-free wavelength, respectively. The temperature, number, and lifetime of cold 171 Yb atoms in one-dimensional lattice are measured. After optimization, the one-dimensional lattice with cold 171Yb atoms is used for developing an ytterbium optical clock.

Kinetic theory of (2+4)-level atom in σ^+ σ^-laser fields

The kinetic theory of （2＋4）-level atoms in σ^＋ -σ^- laser fields is presented. We systemically discuss friction coefficient, momentum diffusion tensor and atomic temperature based on the Fokker-Planck equation. This cooling system is much like that of a （1＋3）-level atom, and the temperature is still limited to the Doppler temperature. Since this cooling system has not been investigated before, this work may be regarded as a necessary complement to the laser cooling theory.

Assessment of the Elasticity of Erythrocytes in Different Physiological Fluids by Laser Traps

In the study of the mechanical properties of the erythrocytes (red blood cells-RBCs) the blood sample is commonly diluted in fluids that do not compromise the integrity of the cells. Fetal bovine serum (FBS), newborn bovine serum (NBBS), and phosphate buffer (PBS) solution with a concentration that can provide the right osmotic pressure are fluids commonly used to dilute the blood samples in such studies. Here we have presented the effect of these fluids on the elastic properties of the RBCs that we studied using laser traps. Two laser traps are directly used to trap and deform the cell by exerting a force distributed on the entire cell. The relative changes in size of the cell are studied as a function of the applied force to investigate any effects on the mechanical deformability of RBCs when the cells are suspended in these fluids. The results have shown that the elasticity of the RBCs in the NBBS is not statistically different from the elasticity of the cells in the PBS solution;however the results for the elasticity of the cells in FBS are found to be significantly higher.

基于二维磁光阱的增强型^(199)Hg冷原子团制备

在精密测量领域中,高效地制备冷原子团具有重要的意义.在光晶格钟里,缩短冷原子团的制备时间可以降低Dick噪声,从而提高光晶格钟的稳定性.本文采用二维磁光阱加推送光的构型提高了三维磁光阱在超高真空环境中的装载率,并通过压缩磁光阱技术降低了原子团温度,实现了用于^(199)Hg光晶格钟的增强型冷原子团制备.实验上通过优化三维和二维磁光阱的失谐量和磁场梯度以及推送光的失谐量和功率等参数,将三维磁光阱的^(199)Hg冷原子装载率增强了51倍,提升至3.1×10^(5)s^(–1),然后使用压缩磁光阱技术将^(199)Hg冷原子团的温度降低至45μK,低于多普勒冷却理论温度.这种基于二维磁光阱的增强型冷原子团制备可在超真空环境下实现对三维磁光阱装载率的高增益,有效地缩短了冷原子团的制备时间,同时也降低了原子团的温度,有利于提高光晶格的转移效率,为其他冷原子实验中冷汞原子团制备提供了有效方案.

CaSH分子高精度电子结构计算及用于激光制冷目标分子的理论分析

作为非对称多原子分子制冷的一个重要目标分子,CaSH的冷却有望打破双原子分子及线性三原子分子在激光冷却中的技术局限.本文使用高精度的EA-EOM-CCSD(electron attachment equation-of-motion coupled cluster singles and doubles)方法,通过cc-pVXZ/cc-pCVXZ(X=T,Q)系列基组外推至基组极限,得到了CaSH基态和3个最低激发态精确的几何结构及基态到激发态的跃迁能.其中,基态X^(2)A′几何结构参数分别为RCaS=2.564A;RSH=1.357A;∠CaSH=91.0°;从X^(2)A′到A^(2)A′,B^(2)A"和C^(2)A′的垂直激发能分别为1.898,1.945和1.966 eV,与已有实验符合得很好.进一步,在3ζ级别基组上,计算了该分子4个最低电子态的势能面,并通过求解核运动方程给出CaS键伸缩、CaSH弯曲两个振动模的频率.最后,理论计算给出的X^(2)A′(0,0,0)态到激发态A^(2)A′(0,0,0),B^(2)A"(0,0,0)和C^(2)A′(0,0,0)跃迁的Frank-Condon(FC)因子分别为0.9268,0.9958和0.9248.结合Frank-Condon因子和激发态寿命分析,本文给出了可能用于CaSH冷却的光学循环,为CaSH的激光冷却提供了理论参考.

冷原子光栅磁光阱的研制及CPT信号的探询

相干布居囚禁原子钟在小型化方面具备不可替代的优势。由于热原子气室内部高压缓冲气体的限制,导致其频率稳定度仍有进一步提升的空间。利用激光冷却原子技术作为替代,可以有效提升其中长期性能。然而,目前的冷原子物理系统仍然相对复杂,不利于原子钟整体系统的集成化和小型化。我们研制了高衍射效率光栅芯片、平面磁阱芯片以及微小型真空腔室,共同构建基于平面核心器件的磁光阱,利用单光束捕获冷原子2×106个。此外,为了简化CPT冷原子钟的激光系统,通过单激光结合时分复用系统的方式,仅用单一Rb D2线激光实现了原子冷却与CPT探询。以上的工作为将来实现微小型化高性能冷原子CPT钟的最终锁定和性能评估奠定了重要理论和技术基础。

PCCL光束对瑞利粒子作用力的理论研究

为了探究部分相干月牙形光束(PCCL)对瑞利粒子的捕获特性,采用广义惠更斯-菲涅耳原理推导了PCCL光束经过ABCD光学系统传输后的交叉谱密度及对瑞利粒子作用力的表达式,对聚焦PCCL光束在焦平面的归一化光强和对瑞利粒子作用力的分布情况进行了软件模拟和理论分析,得到了聚焦PCCL光束的光强和捕获力随光束参量以及焦距变化的规律。结果表明,选取光束阶数n=3、初始腰宽w_(0)=0.1 mm、相干长度d_(0)=6 mm时,经焦距f=12 mm的透镜聚焦后的PCCL光束对高、低折射率粒子均能实现捕获;由于PCCL光束在焦平面处呈现离轴光强分布,峰值光强不在坐标原点,通过调节光束阶数、初始腰宽、相干长度和焦距,可实现对聚焦PCCL光强及瑞利粒子作用力的调控,从而实现聚焦PCCL光束对不同位置处瑞利粒子的灵活捕获。该研究结果为实际聚焦PCCL光束稳定捕获微粒提供了理论依据。

基于玻色凝聚^(87)Rb原子气体相位Ramsey干涉的磁场探测

基于玻色凝聚原子气体的磁场探测可兼顾高灵敏度和高空间分辨率.利用一维光晶格中玻色凝聚^(87)Rb原子气体F=1,m_(F)=1→F=2,m_(F)=-1(F为原子总角动量的量子数,m_(F)为F能级的磁量子数)的双光子跃迁,已实现基于相位Ramsey干涉的精密磁场探测.本研究利用交叉光阱中玻色凝聚^(87)Rb原子气体F=1,m_(F)=1→F=2,m_(F)=0的单光子跃迁,实验研究了频域Ramsey干涉、时域Ramsey干涉及相位Ramsey干涉,并基于相位Ramsey干涉评估了静态磁场测量的灵敏度和空间分辨率.通过对比上述3种Ramsey干涉的实验结果,发现相位Ramsey干涉可有效避免频域Ramsey干涉条纹的畸变和时域Ramsey干涉的退相干效应,从而提高静态磁场测量的灵敏度和准确度.在无磁屏蔽环境中,利用体积为(1.31±0.03)×10^(-9)cm^(3)的玻色凝聚^(87)Rb原子气体,获得了130 nT/√Hz的灵敏度,通过压缩原子气体制备时间和提高信号积累时间,灵敏度有望得到进一步提升.

单离子光频标离子囚禁技术

离子囚禁技术与系统是量子频标、量子计算的核心技术和核心物理参考体系,在精密测量、量子计算、高精度导航定位等领域具有重要的应用价值与应用前景。设计研制了一种基于Paul型离子阱的离子制备与囚禁系统,利用数字PID方法进行多通道多波长激光频率锁定,对离子进行光离化制备、囚禁、激光Doppler冷却。试验系统探测到了单离子的微弱荧光信号,实现了单个离子的稳定囚禁;激光频率漂移由500 MHz稳定至±0.8 MHz,激光冷却温度达到5.53 mK,趋于Doppler冷却极限。

Optical forces on neutral atoms in the presence of fluctuating laser fields:numerical analysis

Doppler cooling of^(88)Sr atoms is studied in the presence of off-resonant red-detuned fluctuating laser fields.Using a semi-classical approach,we show that the relevant physical quantities in the cooling process,such as optical forces,the damping coefficient,Doppler temperature,and atom number in the trap,are strongly affected by the laser amplitude and phase fluctuations.We find that the Doppler cooling limit is higher than the predicted Doppler theory for non-fluctuating lasers.This implies an additional heating mechanism exists due to the laser fluctuations.Furthermore,our numerical analysis shows that the effect of laser power stability on reducing the number of trapped atoms in a magneto-optical trap is more substantial than the effect of laser linewidth.

Clock-transition spectrum of ^(171)Yb atoms in a one-dimensional optical lattice

An optical atomic clock with 171yb atoms is devised and tested. By using a two-stage Doppler cooling technique, the 171Yb atoms are cooled down to a temperature of 6 ± 3 μK, which is close to the Doppler limit. Then, the cold 171Yb atoms are loaded into a one-dimensional optical lattice with a wavelength of 759 nm in the Lamb-Dicke regime. Furthermore, these cold 171yb atoms are excited from the ground-state 1S0 to the excited-state 3P0 by a clock laser with a wavelength of 578 nm. Finally, the 1S0-3P0 clock-transition spectrum of these 171yb atoms is obtained by measuring the dependence of the population of the ground-state 1 S0 upon the clock-laser detuning.

Exact results on cavity cooling in a system of a two-level atom and a cavity field

Using the algebraic dynamical method, this paper investigates the laser cooling of a moving two-level atom coupled to a cavity field. Analytical solutions of optical forces and the cooling temperatures are obtained. Considering Rb atoms as an example, it finds that the numerical results are relevant to the recent experimental laser cooling investigations.