Direct loading of atoms from a macroscopic quadrupole magnetic trap into a microchip trap

We demonstrate the direct loading of cold atoms into a microchip 2-mm Z-trap, where the evaporative cooling can be performed efficiently, from a macroscopic quadrupole magnetic trap with a high loading efficiency. The macroscopic quadrupole magnetic trap potential is designed to be moveable by controlling the currents of the two pairs of anti-Helmholtz coils. The cold atoms are initially prepared in a standard six-beam magneto-optical trap and loaded into the macroscopic quadrupole magnetic trap, and then transported to the atom chip surface by moving the macroscopic trap potential. By means of a three-dimensional absorption imaging system, we are able to optimize the position alignment of the atom cloud in the macroscopic trap and the microchip Z-shaped wire. Consequently, with a proper magnetic transfer scheme, we load the cold atoms into the microchip Z-trap directly and efficiently. The loading efficiency is measured to be about 50%.This approach can be used to generate appropriate ultracold atoms sources, for example, for a magnetically guided atom interferometer based on atom chip.     

Microchip traps and Bose–Einstein condensation

The article gives an overview of the rapidly evolving field of magnetic microchip traps (also called ‘atom chips’) for neutral atoms. Special attention is given to Bose–Einstein condensation in such traps, to the particular properties of microchip trap potentials, and to practical considerations in their design. Scaling laws are developed, which lead to an estimate of the ultimate confinement that chip traps can provide. Future applications such as integrated atom interferometers are discussed. Received: 28 March 2002 / Published online: 14 May 2002     

Production and guidance of pulsed atomic beams on chip

We demonstrated two experimental methods of producing and guiding pulsed atomic beams on chip. One is to trap atoms first in a U-type magneto-optical trap on the chip, then transfer them to the magnetic guide field and push them simultaneously by a continuous force from the power imbalance of the magneto-optical trap laser beams hence the pulsed cold atom beams are produced and move along the magnetic guide to the destination. The other is to trap atoms directly by a H-type magneto-optical trap, then push them to make them move along the magnetic guide field, thus high rate cold atom beams can be produced and guided on the chip.     

Realization of a superconducting atom chip

We have trapped rubidium atoms in the magnetic field produced by a superconducting atom chip operated at liquid helium temperatures. Up to 8.2x10(5) atoms are held in a Ioffe-Pritchard trap at a distance of 440 microm from the chip surface, with a temperature of 40 microK. The trap lifetime reaches 115 s at low atomic densities. These results open the way to the exploration of atom-surface interactions and coherent atomic transport in a superconducting environment, whose properties are radically different from normal metals at room temperature.     

Directly Trapping Atoms in a U-Shaped Magneto-Optical Trap Using a Mini Atom Chip

We experimentally demonstrate the trapping of ^85Rb atoms directly on a chip-size U-shaped magneto-optical trap （U-MOT）. The trap includes a U-shaped wire on the chip, two bias magnetic field coils and laser beams. The capture volume of the U-MOT is theoretically calculated, and the trap is experimentally realized. With 2 A current applied to the U-shaped wire and 2-Gauss horizontal bias field, more than 2 × 10^6 atoms are trapped. In contrast with an ordinary mirror-MOT, this U-MOT captures atoms directly from the background, thus the trap size is greatly reduced. Based on this mini trap scheme, it is possible to realize a chip-size atom trap array for quantum information processing.     

Bose–Einstein condensate on a persistent-supercurrent atom chip

A Bose–Einstein condensate was achieved in a stable magnetic trap on a persistent-supercurrent atom chip with a superconducting closed-loop circuit. We determined precisely the shape of the magnetic trapping potential by systematically controlling the persistent supercurrent. The condensation was verified by time-of-flight imaging and by atom number decay measurements. The measured decay rates agreed quantitatively with numerical simulations on the three-body loss process assuming all of the atoms to be a condensate. We also discuss the feasibility of creating a quasi-one-dimensional Bose gas on our atom chip.     

Trapping and coherent manipulation of a Rydberg atom on a microfabricated device: a proposal

We propose to apply atom-chip techniques to the trapping of a single atom in a circular Rydberg state. The small size of microfabricated structures will allow for trap geometries with microwave cut-off frequencies high enough to inhibit the spontaneous emission of the Rydberg atom, paving the way to complete control of both external and internal degrees of freedom over very long times. Trapping is achieved using carefully designed electric fields, created by a simple pattern of electrodes. We show that it is possible to excite, and then trap, one and only one Rydberg atom from a cloud of ground state atoms confined on a magnetic atom chip, itself integrated with the Rydberg trap. Distinct internal states of the atom are simultaneously trapped, providing us with a two-level system extremely attractive for atom-surface and atom-atom interaction studies. We describe a method for reducing by three orders of magnitude dephasing due to Stark shifts, induced by the trapping field, of the internal transition frequency. This allows for, in combination with spin-echo techniques, maintenance of an internal coherence over times in the second range. This method operates via a controlled light shift rendering the two internal states’ Stark shifts almost identical. We thoroughly identify and account for sources of imperfection in order to verify at each step the realism of our proposal.     

Relevance of sub-surface chip layers for the lifetime of magnetically trapped atoms

We investigate the lifetime of magnetically trapped atoms above a planar, layered atom chip structure. Numerical calculations of the thermal magnetic noise spectrum are performed, based on the exact magnetic Green function and multi layer reflection coefficients. We have performed lifetime measurements where the center of a side guide trap is laterally shifted with respect to the current carrying wire using additional bias fields. Comparing the experiment to theory, we find a fair agreement and demonstrate that for a chip whose topmost layer is metallic, the magnetic noise depends essentially on the thickness of that layer, as long as the layers below have a much smaller conductivity; essentially the same magnetic noise would be obtained with a metallic membrane suspended in vacuum. Based on our theory we give general scaling laws of how to reduce the effect of surface magnetic noise on the trapped atoms.     

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     

Bose--Einstein condensation on an atom chip

This paper reports an experiment of creating Bose-Einstein condensate (BEC) on an atom chip. The chip-based Z-wire current with a homogeneous bias magnetic field creates a tight magnetic trap, which allows for a fast production of BEC. After a 4.17-s forced radio frequency evaporative cooling, a condensate with about 3000 atoms appears. The transition temperature is about 300~nK. This compact system is quite robust, allowing for versatile extensions and further studying of BEC.     

Magnetic trapping of long-lived cold Rydberg atoms

We report on the trapping of long-lived strongly magnetized Rydberg atoms. 85Rb atoms are laser cooled and collected in a superconducting magnetic trap with a strong bias field (2.9 T) and laser excited to Rydberg states. Collisions scatter a small fraction of the Rydberg atoms into long-lived high-angular momentum "guiding-center" Rydberg states, which are magnetically trapped. The Rydberg atomic cloud is examined using a time-delayed, position-sensitive probe. We observe magnetic trapping of these Rydberg atoms for times up to 200 ms. Oscillations of the Rydberg-atom cloud in the trap reveal an average magnetic moment of the trapped Rydberg atoms of approximately -8microB. These results provide guidance for other Rydberg-atom trapping schemes and illuminate a possible route for trapping antihydrogen.     

~(87)Rb玻色-爱因斯坦凝聚体的快速实验制备

采用二维磁光阱产生了-个快速~(87)Rb原子流,并在高真空的三维磁光阱中实现了~(87)Rb原子的快速俘获,进一步采用射频蒸发冷却技术实现了原子云的预冷却,然后将原子转移到远失谐的光学偶极阱中蒸发得到了玻色-爱因斯坦凝聚体.实验上可以在25 s内完成三维磁光阱的装载(约1.0×10~(10)个~(87)Rb原子),然后经过16 s的冷却过程最终在光学偶极阱中获得5.0×10~5个原子的玻色-爱因斯坦凝聚体.实验重点研究了二维磁光阱的优化设计和采用蓝失谐大功率光束对四极磁阱零点的堵塞,抑制四极磁阱中原子的马约拉纳损耗,更加有效地对原子云进行预冷却.     

Atom-optical elements on micro chips

We describe the realization of atom-optical elements as magnetic waveguide potentials, beam splitters and gravitational traps on a microchip. The microchip was produced by electroplating gold conductors on an aluminium-oxide substrate. The conductors are 30–150 μm wide and allow for the generation of waveguides at large distances to the chip surface, where surface effects are negligible. We show that these elements can be integrated on a single chip to achieve complex atom-optical circuits.     

Focusing of an Atomic Beam for the Efficient Loading of an Atom Chip

JETP Letters - A method has been proposed to increase the rate of loading of atoms in a U-magneto-optical trap near an atom chip. The method is based on the focusing of a slow atomic beam into the...     

中性原子的表面双磁光阱及其应用

提出了一种新的采用载流导线的表面双磁光阱(MOT)方案(即双U型导线磁光阱方案)。通过改变中间U型导线中的电流大小,即可将一个双磁阱连续地合并为一个单磁阱,反之亦然。详细计算和分析了上述双U型载流导线磁光阱方案的磁场及其梯度的空间分布,研究发现当导线中的电流为600 A,z方向均匀偏置磁感应强度为-4.0×10-3 T时,双U型导线方案产生的两个磁阱中心的磁场梯度约为1.5×10-3~2.5×10-3 T/cm,结合通常制备磁光阱时所用的三维粘胶(Molasses)光束即可在基底表面附近形成一双磁光阱。理论分析表明在弱光近似下,每个磁光阱中所能俘获的85Rb原子数约为106 量级,相应的磁光阱温度约为270μK。由于双磁光阱可以独立制备,所以双U型导线方案特别适用于制备双样品磁光阱,并用于研究双原子样品的冷碰撞性质。     

非线性磁光效应用于测量磁光阱四极磁场的方案

为了研究磁光阱冷原子团所在区域的磁场大小,从而得出磁场零点附近磁场的微弱变化及其分布。提出利用右旋圆偏振作为探测光场穿过冷原子,根据左右旋圆偏振光场引起的跃迁几率的不同,导致穿过冷原子团零点前后探测场跃迁几率的变化,用来计算零点附近由冷原子团引起的非线性磁光效应,通过这一效应推导出旋转角随磁场大小的变化,从而获得了磁光阱四极磁场零点附近数量级达到10^-13T的磁场值。利用这一效应,同时在理论上获得了不同于以往理论及实验的双峰色散曲线。     

基于磁悬浮大体积交叉光学偶极阱的Dimple光阱装载研究

三维拉曼边带冷却后的铯原子样品装载于一个磁悬浮的大体积交叉光学偶极阱中, 继续加载一个小体积的光学偶极阱后, 实现了Dimple光学偶极阱对铯原子的高效装载. 对不同磁场下磁悬浮大体积光阱的有效装载势能进行理论分析与实验测量, 得出最优化的梯度磁场和均匀偏置磁场, 获得了基于磁悬浮大体积光阱的Dimple光学偶极阱的装载势能曲线, 实现了Dimple光学偶极阱对经拉曼边带冷却后俘获在磁悬浮的大体积光阱中的铯原子样品的有效装载. 比较了Dimple光学偶极阱分别从拉曼边带冷却、大体积的交叉光阱和消除反俘获势后的磁悬浮大体积光阱装载的结果, 将俘获在磁悬浮大体积光阱中的铯原子样品装载到Dimple光学偶极阱, 铯原子样品的密度提高了约15倍.     

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     

Towards surface quantum optics with Bose–Einstein condensates in evanescent waves

We present a surface trap which enables the study of coherent interactions between ultracold atoms and evanescent waves. The trap combines a magnetic Joffe trap with a repulsive evanescent dipole potential. Exploiting the advantages of both approaches this technique improves recent surfaces traps, which are based either on magnetic or optical traps alone. On the one hand, the position of the magnetic trap can be controlled with high precision which makes it possible to move ultracold atoms to the surface of a glass prism or to withdraw the atoms from the surface in a controlled way. On the other hand, the optical potential of the evanescent wave partially compensates for strong attractive surface forces and generates a potential barrier at only a few hundred nanometers from the surface. This barrier prevents the surface potentials from limiting the trap depth of the magnetic trap. The surface trap is probed with ⁸⁷Rb Bose–Einstein condensates (BECs), which are stably positioned at distances from the surfaces below one micrometer.     

Laser cooling without repumping: a magneto-optical trap for erbium atoms

We report on a novel mechanism that allows for strong laser cooling of atoms that do not have a closed cycling transition. This mechanism is observed in a magneto-optical trap (MOT) for erbium, an atom with a very complex energy level structure with multiple pathways for optical-pumping losses. We observe surprisingly high trap populations of over 10(6) atoms and densities of over 10(11) atoms cm(-3), despite the many potential loss channels. A model based on recycling of metastable and ground state atoms held in the quadrupole magnetic field of the trap explains the high trap population, and agrees well with time-dependent measurements of MOT fluorescence. The demonstration of trapping of a rare-earth atom such as erbium opens a wide range of new possibilities for practical applications and fundamental studies with cold atoms.