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.)     

Bright atomic beam by a temporal Zeeman acceleration

A novel method to produce a slow, monochromatic, and bright pulsed atomic beam from a magneto-optical trap by switching the magnetic field of the trap is proposed. A pulsed lithium atomic beam with a brightness of 1.1×10¹⁵ /sr s and a velocity of 13 m/s was produced as an experimental proof of this technique. The conversion efficiency from the trap into the atomic pulse was nearly 100%. Received: 22 October 1999 / Revised version: 15 November 1999 / Published online: 8 March 2000     

Photorefractive effects in long, narrow BSO crystals with applied electric field

In a photorefractive Bi₁₂SiO₂₀ crystal with high applied electric ac field of square-wave shape a fast two-wave coupling response (less than 1 s) and a slow hologram readout decay (minutes) was found for a wavelength of 633 nm. This can be explained by electron–hole transport with two trap levels. An intensity dependence of the slower complementary grating was found. Illuminating with the readout wave without applied electric field leads to a very slow grating decay (many hours). Received: 18 November 1998 / Revised version: 3 February 1999 / Published online: 7 April 1999     

Blue-Sisyphus cooling in cesium gray molasses and antidot lattices

We present an experimental study of the kinetic temperature of cesium atoms interacting with laser beams tuned on the blue side of the transition. In the case of a three-dimensional four-beam molasses, temperatures as low as 800 nK were found. These low temperatures are compatible with a good capture efficiency. The influence of other hyperfine transitions on the temperature is significant. In the presence of a static magnetic field (antidot lattices), the temperatures are slightly higher but show a much weaker dependence on the other hyperfine transitions. Received: 14 May 1998 / Received in final form: 16 October 1998 / Accepted: 2 November 1998     

High-resolution atomic channeling using. velocity-selected atomic beam

High-resolution atomic channeling using velocity-controlled atoms may be able to overcome precision limitations of the conventional atom lithography. We have experimentally clarified the dependence of line width and contrast of atomic patterns in the channeling region on the velocity spread of the atomic source for the first time. Thermal or velocity-selected atomic beams prepared with a one-dimensional magneto-optical trap were employed as the atomic sources. We investigated the channeling characteristics by measuring the frequency shifts of the atomic absorption spectra in an intense standing wave light field. As a result, we can show that narrower line width and higher contrast atomic patterns are obtained as the velocity spread becomes narrower. An atomic pattern with an estimated line width of 57 nm was generated when the velocity spread of the atomic source was almost 50 m/s, that is, 1/6 that of the thermal beam. Received: 16 June 2001 / Published online: 7 November 2001     

Ground state and vortex states of bosons in an anisotropic trap: A variational approach

We propose a simple variational form of the wave function to describe the ground state and vortex states of a weakly interacting Bose gas in an anisotropic trap. The proposed wave function is valid for a wide range of the particle numbers in the trap. It also works well in the case of attractive interaction between the atoms. Further, it provides an easy and fast method to calculate the physical quantities of interest. The results compare very well with those obtained by purely numerical techniques. Using our wave function we have been able to verify, for the first time, the predicted behaviour of the aspect ratio. Received 7 December 1998 and Received in final form 4 February 1999     

Flux-enhanced monochromator by ultrasound excitation of annealed Czochralski-grown silicon crystals

The neutron flux from monochromator crystals can be increased by ultrasound excitation or by strain fields. Rocking curves of both a perfect float-zone silicon crystal and an annealed Czochralski silicon crystal with oxygen precipitates were measured at various levels of ultrasound excitation on a cold-neutron backscattering spectrometer. We find that the effects of the dynamic strain field from the ultrasound and the static strain field from the defects are not additive. Rocking curves were also taken at different ultrasound frequencies near resonance of the crystal/ultrasound-transducer system with a time resolution of 1 min. Pronounced effects of crystal heating are observed, which render the conditions for maximum neutron reflectivity delicate. Received: 19 October 2001 / Accepted: 7 March 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. E-mail: andreas.magerl@krist.uni-erlangen.de     

Atomic beam guide by a one-dimensional magneto-optical trap

An atomic beam has been collimated, compressed, and deflected simultaneously by an atomic beam guide based on an inclined one-dimensional magneto-optical trap (1D-MOT). Isotope-selected rubidium atoms were extracted from the naturally-mixed thermal atomic beam with this method. We could manipulate the transverse displacement of the deflected beam precisely by adjusting the current in the copper rods to generate the quadrupole magnetic field. We could extract more than 50% of the incident atoms as a deflection beam when we combined this deflection technique with the atomic deceleration using a broadband spectral light. Received: 10 December 1998 / Published online: 24 June 1999     

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     

Induced Resonance Processes Accompanying Interaction of the Field of a TEM Trap with Oscillating Charges

We theoretically analyze resonance processes in an electromagnetic trap (TEM trap) formed by a circularly polarized high-frequency standing field of homogeneous plane waves and a uniform static magnetic field aligned with the direction of wave propagation. The regime of resonance amplification of the trap field by an ensemble of initially nonphased oscillators in the absence of a static magnetic field is described. The regime of resonance acceleration of charges from thermal to relativistic velocities for a bounded particle motion in the presence of a static magnetic field is considered. It is shown that charge oscillations in the trap are similar to flutter in mechanical systems. The efficient energy exchange is stipulated by an M-type interaction mechanism.     

Long-range atom-metal-surface interaction and interference of atomic states

The properties of two-dimensional magnetic traps for laser-cooled atoms are analysed using complex functions. The two components of the magnetic field from a series of parallel, infinitely long, current-carrying wires are represented by a single complex number. The regions of the field where paramagnetic atoms can be trapped occur where the magnetic field is zero. The locations of the zeroes of the field are obtained as the solution to a polynomial and the multiplicity m of the solution determines both the 2(m + 1)-pole nature of the trap and the field gradient through the centre. The zeroes of the field can be merged or split by varying the locations of the currents, their strengths or by applying a uniform magnetic field. The theory is applied to magnetic traps created from long thin wires or permanent magnets on a substrate. The properties of a number of magnetic trap configurations used for atom guides are discussed. Received 28 February 2001 and Received in final form 6 July 2001     

Statics and dynamics of a single ferrofluid-peak

We consider a single peak of a ferrofluid resulting from the Rosensweig instability for a small fluid container. Minimizing the total energy of the system by a variational method we determine the shape of the peak in a static field as well as the characteristics of the subcritical bifurcation leading to its formation. The latter are in very good agreement with experiment. Generalizing the approach to dynamic situations we qualitatively reproduce the complicated subharmonic response of the peak to an oscillating part in the external magnetic field found in recent experiments. Received 14 December 1999 and Received in final form 31 May 2000     

Simple and efficient photo-ionization loading of ions for precision ion-trapping experiments

We report a simple and efficient method to load a Paul trap with Ca⁺ ions. A beam of neutral atomic calcium is ionized in a two-step photo-ionization process using uv-diode lasers near 423 nm and 390 nm. Photo-ionization of a calcium beam for loading a Paul trap has first been demonstrated by Kjaergaard et al. The advantages of our method are the use of cheap and easily handled diode-laser systems and the large cross section for field ionization when exciting high-lying Rydberg states. Finally, we discuss the advantages of photo-ionization for ion generation compared to loading by electron bombardment. Received: 24 August 2001 / Revised version: 16 October 2001 / Published online: 23 November 2001     

Free expansion of a Bose–Einstein condensate from an Ioffe–Pritchard magnetic trap

5 rubidium-87 atoms released from an Ioffe–Pritchard magnetic trap is investigated experimentally. The expansion dynamics depend only on the trap frequencies, which are determined independently. The data are in good agreement with the expected expansion of a condensate, and are clearly distinct from the behaviour of a classical gas in the hydrodynamic regime. Received: 3 June 1998/Final version: 25 September 1998     

Magneto-optical trapping of Stark-slowed metastable He atoms

We report on the first successful loading of a magneto-optical trap (MOT) with metastable He atoms from a Stark-slower. Thereby, deceleration of the atoms relies on laser-atom interaction in an inhomogeneous electric field. We show that the results obtained are comparable with early results from other groups achieved with a Zeeman slower. The Stark slower, which is able to fully control the final velocity of the atomic He beam, is the first step in achieving complete spin independent kinematic control based solely on electric fields. Received 2 October 2002 / Received in final form 20 January 2003 Published online 29 April 2003 RID="a" ID="a"e-mail: eichmann@mbi-berlin.de     

Cold atomic beam from a rubidium funnel

We report an experimental demonstration of a continuous, slow and cold beam of rubidium atoms from a two-dimensional magneto-optic trap or atomic funnel. Typically 7.3(7)×10⁸ atoms/s are ejected from the funnel with a variable velocity in the range 2–8 m/s and a temperature of 45–55 μK in the moving frame. This represents the first demonstration of sub-Doppler laser cooling in an atomic beam and temperatures as low as ≈25 μK have been observed. Received: 30 September 1999 / Published online: 5 April 2000     

Magnetic field tomography

Neutral atoms may be trapped via the interaction of their magnetic dipole moment with magnetic field gradients. One of the possible schemes is the cloverleaf trap. It is often desirable to have at hand a fast and precise technique for measuring the magnetic field distribution. We use for instantaneous imaging the equipotential lines of the magnetic field a diagnostic tool which is based on spatially resolved observation of the fluorescence emitted by a hot beam of sodium atoms crossing a thin slice of resonant laser light within the magnetic field region to be investigated. The inhomogeneous magnetic field spatially modulates the resonance condition between the Zeeman-shifted hyperfine sublevels and the laser light and therefore the amount of scattered photons. We apply this technique for mapping the field of our cloverleaf trap in three dimensions under various conditions. Received 20 March 2001 and Received in final form 12 May 2001     

Miniaturized magnetic guide for neutral atoms

We describe the principle and realization of a miniaturized magnetic guide for neutral atoms. The magnetic guide in our experiment is formed by a micrometer-sized current-carrying wire which is attached to a second, thick wire. The conductors are electrically insulated from each other. The combined magnetic field of both conductors provides an approximately linear trapping potential which establishes a magnetic guide along the surface of the thin wire. The miniaturized waveguide is filled with rubidium atoms from a magneto-optical trap (MOT) by first loading the atoms into a spherical magnetic quadrupole trap which is subsequently transformed into the linear potential of the waveguide. As thermal source for Rb atoms we use an alkali metal dispenser which is located close to the center of the MOT. This novel method is compatible with ultrahigh vacuum conditions and we achieved lifetimes of the magnetically trapped atoms up to 100 s. Received: 18 October 1999 / Published online: 24 March 2000     

Spatial subharmonics in a photorefractive semiconductor

The generation of spatial subharmonics is reported in a photorefractive semiconductor (CdTe:Ge) for the first time to our knowledge. Space charge waves with a narrow spatial spectrum are detected in homogeneously illuminated ac-biased CdTe:Ge sample by observation of a well developed low divergent self-diffracted beam. The mobility-lifetime product of the free carriers and the effective trap concentration are estimated from the threshold ac-field measured for different subharmonics at different grating vectors of the generated grating. Received: 5 April 2000 / Published online: 7 June 2000