Investigation of cold rubidium Rydberg atoms in a magneto-optical trap

This paper reports on the results of experiments with cold rubidium Rydberg atoms in a magneto-optical trap. The specific feature of the experiments is the excitation of Rydberg atoms in a small volume within a cloud of cold atoms and the sorting of measured signals and spectra according to the number of detected Rydberg atoms. The effective lifetime of the 37P Rydberg state and its polarizability in a weak electric field are measured. The results obtained are in good agreement with theoretical calculations. It is demonstrated that the localization of the excitation volume in the vicinity of the zero-magnetic-field point makes it possible to improve the spectral resolution and to obtain narrow microwave resonances in Rydberg atoms without switching off the quadrupole magnetic field of the trap. The dependence of the amplitude of dipole-dipole interaction resonances in Rydberg atoms on the number of atoms is measured. This dependence exhibits a linear behavior and agrees with the theory for a weak dipole-dipole interaction.     

Compact magneto-optical trap for rubidium atoms

The characteristics of a magneto-optical trap (MOT) using small-diameter cooling laser beams are considered. Trapping and cooling of Rb atoms from the surrounding gas of warm atoms takes place in the trap. A compact (140 μm) and stable atomic cloud is obtained with a density of 7 × 10¹⁰ cm^?3, which is three orders of magnitude higher than the density of the surrounding gas.     

Investigation of ultracold atoms and molecules in a dark magneto-optical trap

In this paper,ultracold atoms and molecules in a dark magneto-optical trap(MOT) are studied via depumping the cesium cold atoms into the dark hyperfine ground state.The collision rate is reduced to 0.45s-1 and the density of the atoms is increased to 5.6×1011cm-3 when the fractional population of the atoms in the bright hyperfine ground state is as low as 0.15.The vibrational spectra of the ultracold cesium molecules are also studied in a standard MOT and in a dark MOT separately.The experimental results are analyzed by using the perturbative quantum approach.     

Interaction of frequency modulated light pulses with rubidium atoms in a magneto-optical trap

The spatial displacement of the ⁸⁵Rb atoms in a Magneto-Optical Trap (MOT) under the influence of series of frequency modulated light pulse pairs propagating opposite to each other is measured as a function of the time elapsed after the start of the pulse train, and compared with the results of simulations. Adiabatic excitation and consecutive de-excitation take place between the ground 5²S_1/2 (F=3) and the 5²P_3/2 (F'=2, 3, 4) excited levels as the result of the interaction. The displacement of the ⁸⁵Rb atoms is calculated as the solution of simple equation of motion where the expelling force is that arising from the action of the frequency modulated light pulses. The restoring and friction forces of the MOT are taken into account also. The system of Bloch equations for the density matrix elements is solved numerically for transitions between six working hyperfine levels of the atom interacting with the sequence of the frequency modulated laser pulses. According to these simulations, the momentum transferred by one pulse pair is always smaller than the expected 2ħk, (1) where ħ is the Plank constant and k=2π/λ where λ is the wavelength, (2) having a maximum value in a restricted region of variation of the laser pulse peak intensity and the chirp.     

Absorption spectroscopy of cold caesium atoms confined in a magneto-optical trap

Absorption spectra of cold caesium atoms confined in a magneto-optical trap are measured around D_2 line at 852nm with a weak probe beam. Absorption reduction dip due to electromagnetically induced transparency (EIT) effect induced by the cooling/trapping field in a V-type three-level system and a gain peak near the cycling transition are clearly observed. Several mechanisms mixed with EIT effect in a normal V-type three-level system are briefly discussed. A simple theoretical analysis based on a dressed-state model is presented for interpretation of the absorption spectra.     

Continuously transferring cold atoms in caesium double magneto-optical trap

We have established a caesium double magneto-optical trap (MOT) system for cavity-QED experiment, and demonstrated the continuous transfer of cold caesium atoms from the vapour-cell MOT with a pressure of ～ 1×10^-6 Pa to the ultra-high-vacuum (UHV) MOT with a pressure of ～ 8×10^-8 Pa via a focused continuous-wave transfer laser beam. The effect of frequency detuning as well as the intensity of the transfer beam is systematically investigated, which makes the transverse cooling adequate before the atoms leak out of the vapour-cell MOT to reduce divergence of the cold atomic beam. The typical cold atomic flux got from vapour-cell MOT is ～2×10⁷ atoms/s. About 5×10⁶ caesium atoms are recaptured in the UHV MOT.     

Cold rubidium molecules formed in a magneto-optical trap

We report the first observation of translationally cold ( approximately 90 &mgr;K) Rb2 molecules. They are produced in a magneto-optical trap in their triplet ground state. The detection is performed by selective mass spectroscopy after two-photon ionization into Rb+2, resonantly enhanced through the intermediate a (3)Sigma(+)(u)-->2 (3)Pi(g) molecular band. The two rubidium isotopes present very different types of behavior that are interpreted in terms of their respective collisional properties.     

Spectroscopy of the three-photon laser excitation of cold Rubidium Rydberg atoms in a magneto-optical trap

The spectra of the three-photon laser excitation 5S _1/2 → 5P _3/2 → 6S _1/2 nP of cold Rb Rydberg atoms in an operating magneto-optical trap based on continuous single-frequency lasers at each stage are studied. These spectra contain two partly overlapping peaks of different amplitudes, which correspond to coherent three-photon excitation and incoherent three-step excitation due to the presence of two different ways of excitation through the dressed states of intermediate levels. A four-level theoretical model based on optical Bloch equations is developed to analyze these spectra. Good agreement between the experimental and calculated data is achieved by introducing additional decay of optical coherence induced by a finite laser line width and other broadening sources (stray electromagnetic fields, residual Doppler broadening, interatomic interactions) into the model.     

Beta-decay experiments of neutral atoms in a magneto-optical trap

Magneto optical traps (MOT) allow the cooling and storing of neutral atoms in a volume of a few cubic millimeters by use of laser beams and a magnetic field. Such devices offer new and exciting opportunities for precision measurements of radioactive isotopes. Here we present experiments performed with a double-MOT system coupled to the on-line separator TISOL at TRIUMF/Vancouver, Canada. For the first time, the Β-decay of free atoms stored in such a device could be observed. We report on coincidence measurements between beta-particles and the argon recoils in the decay of ³⁷K and ³⁸rm{m}}K. The charge state ratios of the recoil-ions were deduced by Time-Of-Flight separation in an acceleration field. The final goal of those investigations is a precision test of the Standard Model by measuring the –nu-correlation parameter a. This revised version was published online in July 2006 with corrections to the Cover Date.     

铷原子磁光阱中超冷等离子体的形成和演化

在铷原子的磁光阱中,通过光电离冷原子方法和稠密里德堡原子的自发演化方法产生了超冷等离子体。磁光阱中冷却并囚禁了10^7个原子,温度约为500μK,之后用一束脉冲激光将冷原子电离或者激发至高里德堡态,通过调节脉冲激光的能量控制离子数量或者里德堡原子的数量。利用延迟斜坡电场或脉冲电场引出超冷等离子体中的电子,对超冷等离子体的形成和演化进行了研究,并利用库仑势阱模型对实验结果进行了解释。实验结果表明,由于来自长寿命里德堡原子的贡献,里德堡原子自发演化形成的超冷等离子体的寿命比光电离形成的超冷等离子体的寿命长。     

Non-resonant magneto-optical effects in cold atoms

We report a novel nonresonant magneto-optical effect in cold atoms and present the optimized parameters of the biased magnetic field, the incident probe light intensity, and the probe detuning to obtain the maximal signal of the magneto-optical rotation. This detection scheme may further improve the stability of the cold atom clock.     

Laser cooling of 7Li atoms in a magneto-optical trap

A setup for laser cooling and confining of ⁷Li atoms in a magneto-optical trap has been built. The possibility of cooling and trapping of ⁷Li atoms in a wide range of frequency detuning of the cooling laser has been proved experimentally. Independent information on the density and number of ultracold ⁷Li atoms on various ground-state sublevels, as well as on the temperature of the atoms, has been obtained with the use of a probing tunable laser. This information is important for preparing an ultracold plasma and Rydberg matter.     

Sub-doppler laser cooling of thulium atoms in a magneto-optical trap

Sub-Doppler laser cooling in a magneto-optical trap for thulium atoms at a wavelength of 410.6 nm has been experimentally studied. Without any dedicated molasses period of sub-Doppler cooling, the cloud of 3 × 10⁶ atoms at a temperature of 25(5) μK was observed. The measured temperature is significantly lower than the Doppler limit of 240 μK for the cooling transition at 410.6 nm. The high efficiency of the sub-Doppler cooling process is due to a near-degeneracy of the Landé g-factors of the lower 4f ¹³6s ² (J = 7/2) and the upper 4f ¹²5d _3/26s ² (J = 9/2) cooling levels.     

Counting individual 41Ca atoms with a magneto-optical trap

Atom trap trace analysis, a novel method based upon laser trapping and cooling, is used to count individual atoms of 41Ca present in biomedical samples with isotopic abundance levels between 10(-8) and 10(-10). The method is calibrated against resonance ionization mass spectrometry, demonstrating good agreement between the two methods. The present system has a counting efficiency of 2x10(-7). Within 1 h of observation time, its 3-sigma detection limit on the isotopic abundance of 41Ca reaches 4.5x10(-10).     

Loss of cold atoms due to collisions with residual gases in free flight in a magneto-optical trap

The loss rate of cold atoms in a trap due to residual gas collisions differs from that in a free state after the cold atoms are released from the trap. In this paper, the loss rate in a cold rubidium-87 atom cloud was measured in a magneto-optical trap(MOT) and during its free flight. The residual gas pressure was analyzed by a residual gas analyzer, and the pressure distribution in a vacuum chamber was numerically calculated by the angular coefficient method. The decay factor, which describes the decay behavior of cold atoms due to residual gas collisions during a free flight, was calculated. It was found that the decay factor agrees well with theoretical predictions under various vacuum conditions.     

用短程飞行时间吸收谱对铯磁光阱中冷原子温度的测量

介绍采用短程飞行时间吸收谱测量铯原子磁光阱(MOT) 中冷原子温度的基本原理及实验实现.与通常的飞行时间方法不同，采用短程飞行时间吸收谱来测量MOT 中冷原子云的温度.在MOT 区域正下方若干毫米处入射一束圆柱状共振探测光束(实验中对于h=3mm，5mm，8mm的情况均作了研究)，释放冷原子云，在其膨胀和自由下落过程中穿过探测光束，即可由光电探测器测得飞行时间吸收谱，由此推得MOT中冷原子的温度. 关键词： 磁光阱 冷原子 飞行时间 短程飞行时间 铯原子     

Single atoms transferring between a magneto-optical trap and a far-off-resonance optical dipole trap

Based on our work on single cesium atoms trapped in a large-magnetic-gradient vapour-cell magneto-optical trap (MOT), the signal-to-noise ratio (SNR) is remarkably improved. Also a far-off-resonance optical dipole trap (FORT) formed by a strongly-focused 1064~nm single frequency Nd:YVO₄ laser beam is introduced. One cesium atom is prepared in the MOT, and then it can transfer successfully between the MOT and the FORT which is overlapped with the MOT. Utilizing the effective transfer, the lifetime of single atoms trapped in the FORT is measured to be 6.9± 0.3~s. Thus we provide a system where the atomic qubit can be coherently manipulated.     

用吸收法对铯原子磁光阱中冷原子数目的测量

介绍了吸收法测量冷原子数的原理以及对铯原子气室磁光阱中俘获的冷原子数目的测量过程及结果. 与通常的荧光收集法相比，在原理上与静止二能级原子同共振单模光场作用的模型更加接近，同时大大减小了测量中的误差累积，提高了测量精度. 测得的冷原子数为(8±0.3)×10⁶，同时还利用测得的阱中俘获的稳态冷原子数和磁光阱中冷原子的寿命间接获得了磁光阱的俘获率. 关键词： 激光冷却与俘获 磁光阱 冷原子数目 俘获率     

Observation of nonlinear optical recoil-induced resonances in a dark magneto-optical trap

Nonlinear optical recoil-induced resonances have been observed in a gas of cold rubidium atoms trapped in a dark magneto-optical trap. These resonances are used to measure the temperature and velocity distribution of the cold atoms. The velocity distribution of the atoms in the dark magneto-optical trap has an excessive amount of fast atoms as compared to the Maxwell distribution and to the distribution in a standard magneto-optical trap.