Meissner effect in superconducting microtraps

We report on the realization and characterization of a magnetic microtrap for ultracold atoms near a straight superconducting Nb wire with circular cross section. The trapped atoms are used to probe the magnetic field outside the superconducting wire. The Meissner effect shortens the distance between the trap and the wire, reduces the radial magnetic-field gradients, and lowers the trap depth. Measurements of the trap position reveal a complete exclusion of the magnetic field from the superconducting wire for temperatures lower than 6 K. As the temperature is further increased, the magnetic field partially penetrates the superconducting wire; hence the microtrap position is shifted towards the position expected for a normal-conducting wire.     

Magnetic conveyor belt transport of ultracold atoms to a superconducting atomchip

We report the realization of a robust magnetic transport scheme to bring >3 × 10⁸ ultracold ⁸⁷Rb atoms into a cryostat. The sequence starts with standard laser cooling and trapping of ⁸⁷Rb atoms, transporting first horizontally and then vertically through the radiation shields into a cryostat by a series of normal- and superconducting magnetic coils. Loading the atoms in a superconducting microtrap paves the way for studying the interaction of ultracold atoms with superconducting surfaces and quantum devices requiring cryogenic temperatures.     

A compact UHV package for microfabricated ion-trap arrays with direct electronic air-side access

We have demonstrated a new apparatus for operating microfabricated ion-trap arrays in a compact ultra-high-vacuum setup with excellent optical and electrical access. The approach uses conventional components, materials and techniques in a unique fashion. The microtrap chip is mounted on a modified ceramic leadless chip carrier, the conductors of which serve as the vacuum feedthrough. The chip carrier is indium-sealed to stainless-steel components to form vacuum seals, resulting in short electrical path lengths of ≤20 mm from the trap electrodes under vacuum to air side. The feedthrough contains conductors for the radio-frequency trap drive, as well as 42 conductors for DC electrodes. Vacuum pressures of ～1 × 10^?11 mbar are achieved, and ions have been confined and laser cooled in a microtrap chip. The apparatus enables accurate measurements of radio-frequency voltage amplitudes on the trap electrodes, yielding an excellent agreement between measured and modelled trap efficiencies. This feature is of significant use in establishing initial operation of new devices. The principle of the connectivity scheme presented here is applicable to larger ceramic chip carriers containing many more conductors.     

A high-resolution time-of-flight mass spectrometer for the detection of ultracold molecules

We have realized a high-resolution time-of-flight mass spectrometer combined with a magneto-optical trap. The spectrometer enables excellent optical access to the trapped atomic cloud using specifically devised acceleration and deflection electrodes. The ions are extracted along a laser beam axis and deflected onto an off-axis detector. The setup is applied to detect atoms and molecules photoassociated from ultracold atoms. The detection is based on resonance-enhanced multi-photon ionization. Mass resolution up to m/Δm_rms=1000 at the mass of ¹³³Cs is achieved. The performance of this spectrometer is demonstrated in the detection of photoassociated ultracold ⁷Li¹³³Cs molecules near a large signal of ¹³³Cs ions. PACS 07.75.+h; 32.80.Rm; 37.10.Gh     

Trapping of ultracold atoms in a 3He/4He dilution refrigerator

We describe the preparation of ultracold atomic clouds in a dilution refrigerator. The closed-cycle ³He/⁴He cryostat was custom made to provide optical access for laser cooling, optical manipulation and detection of atoms. We show that the cryostat meets the requirements for cold atom experiments, specifically in terms of operating a magneto-optical trap, magnetic traps and magnetic transport under ultrahigh vacuum conditions. The presented system is a step toward the creation of a quantum hybrid system combining ultracold atoms and solid-state quantum devices.     

Development of an apparatus for cooling <Superscript>6</Superscript>Li-<Superscript>87</Superscript>Rb Fermi-Bose mixtures in a light-assisted magnetic trap

We describe an experimental setup designed to produce ultracold trapped gas clouds of fermionic ⁶Li and bosonic ⁸⁷Rb. This combination of alkali metals has the potential to reach deeper Fermi degeneracy with respect to other mixtures since it allows for improved heat capacity matching which optimizes sympathetic cooling efficiency. Atomic beams of the two species are independently produced and then decelerated by Zeeman slowers. The slowed atoms are collected into a magneto-optical trap and then transferred into a quadrupole magnetic trap. An ultracold Fermi gas with temperature in the 10^?3 T _F range should be attainable through selective confinement of the two species via a properly detuned laser beam focused in the center of the magnetic trap.     

Applications of integrated magnetic microtraps

Lithographically fabricated circuit patterns can provide magnetic guides and microtraps for cold neutral atoms. By combining several such structures on the same ceramic substrate, we have realized the first ‘atom chips’ that permit complex manipulations of ultracold trapped atoms or de Broglie wave packets. We show how to design magnetic potentials from simple conductor patterns and we describe an efficient trap-loading procedure in detail. Applying the design guide, we describe some new microtrap potentials, including a trap which reaches the Lamb–Dicke regime for rubidium atoms in all three dimensions, and a rotatable Ioffe–Pritchard trap, which we also demonstrate experimentally. Finally, we demonstrate a device allowing independent linear positioning of two atomic clouds which are very tightly confined laterally. This device is well suited for the study of one-dimensional collisions. Received: 27 July 2000 / Revised version: 30 August 2000 / Published online: 22 November 2000     

Spin coupling between cold atoms and the thermal fluctuations of a metal surface

We describe an experiment in which Bose-Einstein condensates and cold atom clouds are held by a microscopic magnetic trap near a room-temperature metal wire 500 microm in diameter. The lifetime for atoms to remain in the microtrap is measured over a range of distances down to 27 microm from the surface of the metal. We observe the loss of atoms from the microtrap due to spin flips. These are induced by radio-frequency thermal fluctuations of the magnetic field near the surface, as predicted but not previously observed.     

Prospects for sympathetic cooling of molecules in electrostatic, ac and microwave traps

We consider how trapped molecules can be sympathetically cooled by ultracold atoms. As a prototypical system, we study LiH molecules co-trapped with ultracold Li atoms. We calculate the elastic and inelastic collision cross sections of ⁷LiH + ⁷Li with the molecules initially in the ground state and in the first rotationally excited state. We then use these cross sections to simulate sympathetic cooling in a static electric trap, an ac electric trap, and a microwave trap. In the static trap we find that inelastic losses are too great for cooling to be feasible for this system. The ac and microwave traps confine ground-state molecules, and so inelastic losses are suppressed. However, collisions in the ac trap can take molecules from stable trajectories to unstable ones and so sympathetic cooling is accompanied by trap loss. In the microwave trap there are no such losses and sympathetic cooling should be possible.     

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.     

一维强相互作用极化费米子的相图

文章首先简要评述了目前强相互作用的极化冷费米原子体系的研究现状.在三维,人们对该体系基态存在着不同认识.为对这个问题有进一步了解,文章探讨了一维强相互作用极化费米气体.在均匀情况下,这是一个可积系统,可以得到该体系的一个严格相图.作者发现了一种非均匀的超流相在相空间占主导地位.在有外加束缚势的实验情况下,通过局域密度泛函近似,作者发现了两种新颖的相分离相.     

An experimental approach for investigating many-body phenomena in Rydberg-interacting quantum systems

Recent developments in the study of ultracold Rydberg gases demand an adwanced level of experimental sophistication, in which high atomic and optical densities must be combined with excellent control of external fields and sensitive Rydberg atom detection. We describe a tailored experimental system used to produce and study Rydberg-interacting atoms excited from dense ultracold atomic gases. The experiment has been optimized for fast duty cycles using a high flux cold atom source and a three beam optical dipole trap. The latter enables tuning of the atomic density and temperature over several orders of magnitude, all the way to the Bose--Einstein condensation transition. An elec- trode structure surrounding the atoms allows for precise control over electric fields and single-particle sensitive field ionization detection of Rydberg atoms. We review two experiments which highlight the influence of strong Rydberg---Rydberg interactions on different many-body systems. First, the Rydberg blockade effect is used to pre-structure an atomic gas prior to its spontaneous evolution into an ultracold plasma. Second, hybrid states of photons and atoms called dark-state polaritons are studied. By looking at the statistical distribution of Rydberg excited atoms we reveal correlations between dark-state polaritons. These experiments will ultimately provide a deeper understanding of many-body phenomena in strongly-interacting regimes, including the study of strongly-coupled plasmas and interfaces between atoms and light at the quantum level.     

Improved method to retrieve aerosol optical properties from combined elastic backscatter and Raman lidar data

Two methods to load a microtrap consisting of two concentric microwire loops of radii 300 and 660 μm carrying oppositely oriented currents are demonstrated. Atoms can be directly loaded into the microtrap from a surface magneto-optical trap or alternatively using a far-off resonance optical dipole trap (FORT) as an intermediate step. About 1 × 10^{5 87}Rb atoms can be loaded into the microtrap using either technique although the FORT achieves a lower temperature. The FORT is well suited to loading a linear array of 3 microtraps that are aligned with the propagation direction of the infrared laser. Atoms can be trapped in either the $5S_{1/2}\;F=1$ or 2 ground state hyperfine level. The position of the microtrapped atom cloud can be precisely adjusted using a bias magnetic field over a distance of 350 to slightly <50 μm from the atom chip surface.     

Experimental Observation of Spin-Exchange in Ultracold Fermi Gases

We experimentally study the spin exchange collision in ultracold~(40) K Fermi gases. The quadratic Zeeman shift,trap potential and temperature of atomic cloud will influence on the spin changing dynamics. Dependences of the spin components populations on the external bias magnetic field, the optical trap depth and the temperature of atomic cloud are experimentally investigated. The spin exchange from the initial states to the final state are observed for different initial states. This work shows an interesting process of reaching equilibrium by redistribution among the spin states with the spin exchange collision in an ultracold large-spin Fermi gas.     

Nanoscale atomic waveguides with suspended carbon nanotubes

We propose an experimentally viable setup for the realization of one-dimensional ultracold atom gases in a nanoscale magnetic waveguide formed by single doubly-clamped suspended carbon nanotubes. We show that all common decoherence and atom loss mechanisms are small, guaranteeing a stable operation of the trap. Since the extremely large current densities in carbon nanotubes are spatially homogeneous, our proposed architecture allows for creation of a very regular trapping potential for the atom cloud. Adding a second nanowire allows creation of a double-well potential with a moderate tunneling barrier which is desired for tunneling and interference experiments with the advantage of tunneling distances being in the nanometer regime. PACS 03.75.Gg; 03.75.Dg; 73.63.Fg     

Ultracold superstrings in atomic boson-fermion mixtures

We propose a setup with ultracold atomic gases that can be used to make a nonrelativistic superstring in four spacetime dimensions. In particular, we consider for the creation of the superstring a fermionic atomic gas that is trapped in the core of a vortex in a Bose-Einstein condensate. We explain the required tuning of experimental parameters to achieve supersymmetry between the fermionic atoms and the bosonic modes describing the oscillations in the vortex position. Furthermore, we discuss the experimental consequences of supersymmetry.     

Ultracold Atomic Fermi–Bose Mixtures in Bichromatic Optical Dipole Traps: A Novel Route to Study Fermion Superfluidity

The study of low density, ultracold atomic Fermi gases is a promising avenue to understand fermion superfluidity from first principles. One technique currently used to bring Fermi gases in the degenerate regime is sympathetic cooling through a reservoir made of an ultracold Bose gas. We discuss a proposal for trapping and cooling of two-species Fermi–Bose mixtures into optical dipole traps made from combinations of laser beams having two different wavelengths. In these bichromatic traps it is possible, by a proper choice of the relative laser powers, to selectively trap the two species in such a way that fermions experience a stronger confinement than bosons. As a consequence, a deep Fermi degeneracy can be reached having at the same time a softer degenerate regime for the Bose gas. This leads to an increase in the sympathetic cooling efficiency and allows for higher precision thermometry of the Fermi–Bose mixture.     

Cold cesium molecules produced directly in a magneto-optical trap

We report on the observation of ultracold ground electric-state cesium molecules produced directly in a magneto- optical trap with a good signal-to-noise ratio. These molecules arise from the photoassociation of magneto-optical trap lasers and they are detected by resonantly enhanced multiphoton ionization technology. The production rate of ultracold cesium molecules is up to 4×10⁴ s^-1. We measure the characteristic time of the ground electric-state cesium molecules generated in the experiment and investigate the Cs₂⁺ molecular ion intensity as a function of the trapping laser intensity and the ionization pulse laser energy. We conclude that the production of cold cesium molecules may be enhanced by using appropriate experimental parameters, which is useful for future experiments involving the production and trapping of ultracold ground electric-state molecules.     

激光冷却获得高亮度的亚稳态惰性气体原子束和原子阱

高强度的亚稳态惰性原子束流在原子分子物理实验研究中具有广泛的应用.使用射频电离方法和激光横向冷却技术制备了高强度的亚稳态氪原子束流,并使用数值模拟方法对横向冷却激光场中的原子径迹进行了分析.通过激光诱导荧光光谱方法测量原子束的束流特性,结果显示,横向冷却后在束流源下游230 cm处的原子束流强度达1.6atoms/(s*sr),束流强度提高了两个量级.利用这种高强度原子束流,我们成功囚禁了1.3×10¹⁰个亚稳态⁸⁴Kr原子,同时冷原子装载速率达到了3.0×10¹¹atoms/s;并利用该装置成功地实现了高亮度的亚稳态氩原子束和原子阱. 关键词： 横向冷却 原子束 原子阱 惰性气体