Atom chip based fast production of Bose–Einstein condensate

We have developed a simple method for the fast and efficient production of a Bose–Einstein condensate (BEC) on an atom chip. By using a standard six-beam magneto-optical trap and light-induced atom desorption for loading, 3×10^{7 87}Rb atoms are collected within 1 s and loaded into a small-volume magnetic potential of the chip with high efficiency. With this method, a BEC of 3×10³ atoms is realized within a total time of 3 s. We can realize a condensate of up to 2×10⁴ atoms by reducing three-body collisions. The present system can be used as a fast and high-flux coherent matter-wave source for an atom interferometer. PACS 03.75.Be; 32.80.Pj; 39.25.+k     

Method for obtaining high phase space density in a surface-mounted atom trap

We describe a method for obtaining a high phase space density of alkali atoms in a surface-mounted microscopic atom trap created above a transparent conductor or permanent magnet on a substrate prism. We show that the peak value of the phase space density can locally reach the level of 10^-2 when the microtrap is loaded with atoms from a gravito-optical surface trap. Initial spin polarization of the atoms is not required. PACS 32.80.Pj; 39.25.+k; 03.75.Be     

Nanolithography with metastable helium atoms in a high-power standing-wave light field

We have created periodic nanoscale structures in a gold substrate with a lithography process using metastable triplet helium atoms that damage a hydrophobic resist layer on top of the substrate. A beam of metastable helium atoms is transversely collimated and guided through an intense standing-wave light field. Compared to commonly used low-power optical masks, a high-power light field (saturation parameter of 10⁷) increases the confinement of the atoms in the standing wave considerably, and makes the alignment of the experimental setup less critical. Due to the high internal energy of the metastable helium atoms (20 eV), a dose of only one atom per resist molecule is required. With an exposure time of only eight minutes, parallel lines with a separation of 542 nm and a width of 100 nm (one-eleventh of the wavelength used for the optical mask) are created.PACS 32.80.Lg; 39.25.+k; 81.16.Nd     

Laser cooling and trapping of Yb from a thermal source

We have successfully loaded a magneto-optic trap for Yb atoms from a thermal source without the use of a Zeeman slower. The source is placed close to the trapping region so that it provides a large flux of atoms that can be cooled and captured. The atoms are cooled on the transition at 398.9 nm. We have loaded all seven stable isotopes of Yb into the trap including the rarest isotope, ¹⁶⁸Yb. For the most abundant isotope (¹⁷⁴Yb), we load more than 10⁸ atoms into the trap within 1 s. We have characterized the source by studying the loading rate and the loss rate for different isotopes and at different trapping powers. We extract values for the loss rate due to collisions and due to branching into low-lying metastable levels. At the highest trap densities, we find evidence of additional loss due to intra-trap collisions.Received: 15 February 2004, Published online: 23 March 2004PACS: 32.80.Pj Optical cooling of atoms; trapping - 42.50.Vk Mechanical effects of light on atoms, molecules, electrons, and ions     

原子束在光定波场中的聚焦研究

建立了描述原子束在光定波场中聚焦行为的理论模型并通过数值计算给出原子在光驻波场中的运动轨迹,针对不同情况模拟了原子在基底上沉积的堆积图形.     

High power narrow linewidth laser at 556 nm for magneto-optical trapping of ytterbium

We present a high-power and narrow-linewidth laser for intercombination magneto-optical trapping of ytterbium (Yb) atoms using the 6s^{2 1}S₀–6s6p ³P₁ transition. The system generates 415 mW of continuous wave laser radiation at 556 nm with a linewidth of less than 100 kHz. It is based on a commercial 1 W fiber laser with a frequency doubling stage. Up to 58% frequency doubling efficiency is obtained at an input power of 0.5 W by using a lithium triborate crystal as a nonlinear medium. The system has been successfully used for laser cooling of Yb atoms. PACS  42.55.Wd; 42.60.By; 42.79.Nv     

Mapping a cloud of ultra-cold atoms onto a miniature storage ring

We describe how to realize magnetic and magneto-optical confinement of ultra-cold atoms in a torus with adjustable diameter and how an elliptical cloud of ultra-cold atoms can be adiabatically transformed to have a toroidal shape. An experiment with cold ⁸⁷Rb atoms demonstrates the feasibility of shape transformations. These techniques can be used for atom interferometry and quantum computation. PACS 03.75.Be; 32.80.Pj; 03.67.Lx     

Quantum-degenerate gases of Ytterbium atoms

Evaporative cooling of ultracold Yb atoms near the quantum-degenerate regime was experimentally studied. Three bosons of ¹⁷⁰Yb, ¹⁷²Yb, ¹⁷⁶Yb and two fermions of ¹⁷¹Yb and ¹⁷³Yb were evaporatively cooled in a crossed far-off resonant trap (FORT). We observed that ¹⁷⁰Yb and ¹⁷²Yb were not concentrated into the crossed region. We found that, in the cases of ¹⁷⁶Yb atoms, atoms were concentrated well into the crossed region. The following evaporative cooling in the crossed region, however, did not work well. We performed the simultaneous trapping and sympathetic cooling in the crossed FORT by use of ¹⁷²Yb-174Yb, ¹⁷⁴Yb-¹⁷⁶Yb, ¹⁷²Yb-¹⁷⁶Yb, and ¹⁷¹Yb-¹⁷⁴Yb pairs. We observed that evaporative cooling worked well. This result shows that we succeeded in the enhancement of the atom collision rate. Especially, by use of ¹⁷⁴Yb-¹⁷⁶Yb mixture, we obtained cold ¹⁷⁶Yb whose phase space density was 0.02. We observed a large atom loss, which limited the further sympathetic evaporative cooling. We also evaporatively cooled ¹⁷⁴Yb in a 1D optical lattice. Evaporative cooling worked very well because the atoms were initially trapped at a high density. After evaporative cooling, we obtained very cold atoms, and T/T _F was estimated to be 1.2.     

Loading rate of Yb<Superscript>+</Superscript> loaded through photoionization in radiofrequency ion trap

We investigate the loading rate of Yb⁺ ions loaded through photoionization in a radiofrequency trap. The absolute or relative number of the loaded trapped ions is measured by use of an electric resonance of the secular motion. This method is applicable even in the presence of anharmonicity. In two-color photoionization, where the first-excitation laser drives the ¹S₀–¹P₁ transition in the Yb atom and the second one ionizes the atom from the ¹P₁ state, the loading rate is at its highest by the excitation of the ionization potential. A similar loading rate is observed at the second-laser wavelength around 369.5 nm, which is the wavelength for the cooling transition of Yb⁺. We estimate the loading cross section to be 40(15) Mb for the two-color excitation of the ionization potential. The excitation of the Yb atoms in the Rydberg states is detected by the enhancement of the loading rate. By irradiation with only the first-excitation laser, Yb⁺ is produced at a rate three orders of magnitude smaller than that when the non-resonant two-photon absorption from the ¹P₁ state is the dominant process. We also measure the charge-exchange rate between Yb⁺ and Yb, and discuss its effect on isotope-selective photoionization loading.     

A frequency-doubled laser system producing ns pulses for rubidium manipulation

We have constructed a pulsed laser system for the manipulation of cold ⁸⁷Rb atoms. The system combines optical telecommunications components and frequency doubling to generate light at 780 nm. Using a fast, fibre-coupled intensity modulator, we sliced output from a continuous laser diode into pulses with a length between 1.3 and 6.1 ns and a repetition frequency of 5 MHz. These pulses are amplified using an erbium-doped fibre amplifier, and frequency-doubled in a periodically poled lithium niobate crystal, yielding a peak power up to 12 W. Using the resulting light at 780 nm, we demonstrate Rabi oscillations on the F=2,m_F=+2↔F^′=3, m^′ _F=+3-transition of a single ⁸⁷Rb atom. PACS 32.80.Qk; 39.25.+k; 42.55.-f     

Paramagnetic Faraday rotation with spin-polarized ytterbium atoms

We report the observation of paramagnetic Faraday rotation of spin-polarized ytterbium (Yb) atoms. As the atomic samples, we used an atomic beam, released atoms from a magneto-optical trap (MOT), and trapped atoms in a far-off-resonant trap (FORT). Since Yb is diamagnetic and includes a spin-1/2 isotope, it is an ideal sample for spin physics, such as quantum non-demolition measurement of spin (spin QND), for example. From the results of the rotation angle, we confirmed that the atoms were almost perfectly polarized. PACS 32.80.Bx; 32.80.Pj; 42.25.Lc     

一种新颖的全光型表面原子(分子)漏斗

提出了一种产生全光型表面原子(分子)漏斗的新方案.采用红失谐高斯激光束照明由柱面透镜组成的光学系统，可在透镜焦平面附近产生横向漏斗形光强分布，以构成一表面光波导型原子漏斗.计算了漏斗的光强分布及其光学偶极势与偶极力分布.研究结果表明：该原子漏斗可用于冷原子(分子)的表面光波导、分束器和干涉仪以及微阱囚禁的有效装载，因而在集成原子光学及其原子芯片的研究中有着重要的应用. 关键词： 原子漏斗 分子漏斗 光学偶极势 原子芯片     

Microscopic electro-optical atom trap on an evanescent-wave mirror

We put forward the idea of a surface-mounted microscopic electro-optical atom trap. The trap is formed on an evanescent-wave atom mirror by the strongly localized static electric field of two oppositely charged transparent electrodes placed close to each other. The electrodes are embedded in a refractive-index-matched thin dielectric layer on the surface of a glass prism. In our example, the phase-space density in the trap center reaches 0.1, when the trap is loaded with atoms from a gravito-optical surface trap.Received: 16 October 2003PACS: 32.80.Pj Optical cooling of atoms; trapping - 39.25. + k Atom manipulation (scanning probe microscopy, laser cooling, etc.)     

Fluorescence from doubly driven four-level atoms

The unusually narrow features in the fluorescence from ⁸⁵Rb driven by two laser fields L1 and L2, reported in [1], are explained on the basis of a four-level density matrix calculation. The L2 laser enables atom transfer to the fluorescing levels connected by the strong L1 laser. In turn the L1 laser causes the Autler-Townes splitting of the upper levels connected by L2 laser. These two effects are shown to maximise fluorescence within a narrow spectral range of the scanned L2 laser due to velocity selection of atoms from co-propagating and counter propagating L1 and L2 lasers. The analysis reveals the existence of narrow spectral features from a collection of atoms at room temperature even in the absence of induced coherences between the levels.Received: 2 July 2004, Published online: 21 September 2004PACS: 42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift - 32.80.Bx Level crossing and optical pumping     

Simple and efficient magnetic transport of cold atoms using moving coils for the production of Bose–Einstein condensation

We have developed a simple magnetic transport method for the efficient loading of cold atoms into a magnetic trap. Laser-cooled ⁸⁷Rb atoms in a magneto-optical trap (MOT) are transferred to a quadrupole magnetic trap and they are then transported as far as 50 cm by moving magnetic trap coils with a low excess heating of atoms. A light induced atom desorption technique helps to reduce the collision loss during the magnetic transport. Using this method, we can load cold ⁸⁷Rb atoms into a magnetic trap in an ultra high vacuum chamber with high efficiency, and we can produce ⁸⁷Rb condensate atoms. PACS 39.25.+k; 32.80.Pj; 03.75.Pp     

Frequency response measurement of high-speed photodetectors using the spectrum power method in a delay self-heterodyne system

We report on a photoionization scheme for controlled loading of ⁸⁸Sr⁺ ions into a radio-frequency (rf) ion trap. The two-step doubly-resonant process drives the ⁸⁸Sr atom on the 5s^{2 1} S ₀ – 5s5p¹ P ₁ transition at 461 nm using a frequency-doubled diode laser, and then excites the atom to the autoionizing (4d²+5p²) ¹ D ₂ state with 405 nm light from a free-running diode laser. This method of trap loading is quantitatively compared to electron bombardment loading, and shown to reduce the Sr vapour pressure required to load by four orders of magnitude. It also provides more than an order of magnitude reduction in the day-to-day variation of the voltages required to compensate micromotion. We additionally introduce a two-step atomic source consisting of an oven and hotplate, which reduces the number of impurities evaporated towards the trap. This is shown to significantly reduce fluctuations in required micromotion compensation voltages. The demonstrated reduction in flux and increased source purity are expected to improve the reliability of trap operation for precision ion-trap experiments. PACS 32.80.Fb; 32.80.Pj; 39.10.+j     

Magneto-Optical Trapping of Ytterbium Atoms with a 398.9nm Laser

We report the realization of ytterbium magneto-optical trap （MOT） operating on the dipole-allowed ^1S0 - ^1P1 transition at 398.9nm. The MOT is loaded by a slowed atomic beam produced by a Zeeman slower. All seven stable isotopes of Yb atoms could be trapped separately at different laser detuning values. Over 10^7 174 Yb atoms are collected in the MOT, whereas the atom number of fermionic isotope ^171Yb is roughly 2.3 × 10^6 due to a lower abundance. Without the Zeeman slower the trapped atom numbers are one order of magnitude lower. Both the even and odd isotopes are recognized as excellent candidates of optical clock transition, so the cooling and trapping of ytterbium atoms by the blue MOT is an important step for building an optical clock.     

Simultaneous magneto-optical trapping of lithium and ytterbium atoms towards production of ultracold polar molecules

We have successfully implemented the first simultaneous magneto-optical trapping (MOT) of lithium (⁶Li) and ytterbium (¹⁷⁴Yb) atoms towards production of ultracold polar molecules of LiYb. For this purpose, we developed the dual atomic oven which contains both atomic species as an atom source and successfully observed the spectra of the Li and Yb atoms in the atomic beams from the dual atomic oven. We constructed the vacuum chamber including the glass cell with the windows made of zinc selenium (ZnSe) for the CO₂ lasers, which are the useful light sources of optical trapping for evaporative and sympathetic cooling. Typical atom numbers and temperatures in the compressed MOT are 7×10³ atoms, 640 μK for ⁶Li, 7×10⁴ atoms, and 60 μK for ¹⁷⁴Yb, respectively.     

Selective detection of minor isotope lines in saturated absorption spectra by absorption filtering of major isotope lines

We demonstrate a simple method that can be used to detect minor isotope lines in a saturated absorption spectrum by the absorption filtering of major isotope lines. We investigate this method for use in the spectroscopy of the ¹S₀-¹P₁ transition in Yb at 399 nm by controlling the density of Yb atoms by varying the discharge current of a hollow cathode lamp. The performance of an extended-cavity laser diode using a high-power ultraviolet diode chip is also analyzed.     

利用蓝失谐激光诱导微型光学偶极阱中冷原子间的光助碰撞提高单原子制备概率

借助于微米尺度的远失谐光学偶极阱(FORT)中蓝失谐光的光助碰撞效应与反馈控制系统,文章在实验上实现了FORT中单个原子的高效制备.结合原子的势能曲线,分析了原子在红失谐光和蓝失谐光作用下的光助碰撞效应,并且在实验上得到红失谐光诱导下单原子的制备概率约50%,蓝失谐光诱导下单原子的制备概率约80%.通过反馈控制系统,当原子数目小于1时,反馈控制使磁场梯度减小以快速俘获原子,当原子数目大于1时,反馈控制开启蓝失谐光场,使得原子一个个逃逸出阱中,最终实现了FORT中单原子的制备概率约95%,为下一步偶极阱的二维扩展奠定了基础.通过HBT实验测量FORT中单原子发出光子的统计特性,得到二阶相干度g(2)(τ=0)=0.08.