Efficient magnetic guiding and deflection of atomic beams with moderate velocities

We have studied guidance and deflection of a beam of cesium atoms by a strong toroidal magnetic quadrupole field. The beam guide is made from permanent magnets sustaining a radial field gradient of 2.8 T/cm. Atoms with moderate longitudinal velocities ranging from 30 m/s to 70 m/s were inserted across the 10-mm-diameter aperture of a 24.5° arc with radius 300 mm. We have measured transmission and beam divergence and find good agreement with ray-tracing calculations and analytical estimates. The magnetic beam guide allows for 100% transmission of heavy atoms over large angles. Received: 9 November 1998 / Revised version: 6 April 1999 / Published online: 30 July 1999     

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     

Manipulation of cold atoms by an adaptable magnetic reflector

Adaptive optics for cold atoms has been experimentally realized by applying a bias magnetic field to a static magnetic mirror. The mirror consist of a 12-mm-diameter piece of commercial videotape, having a sine wave of wavelength 25.4 μm recorded in a single track across its width, curved to form a concave reflector with radius of curvature R=54 mm. We have studied the performance of the mirror by monitoring the evolution of a 24 μK cloud of ⁸⁵Rb atoms bouncing on it. A uniform static external magnetic field was added to the mirror field causing a corrugated potential from which the atoms bounce with increased angular spread. The characteristic angular distribution of the surface normal is mapped at the peak of the bounce for atoms dropped from a height of R/2 and at the peak of the second bounce for a drop height of R/4. In a second experiment a time-dependent magnetic field was applied and the angular distribution of the cloud was measured as a function of field frequency. In this scheme we demonstrate a corrugated potential whose time-dependent magnitude behaves like a diffraction grating of variable depth. Finally a rotating field was added to generate a corrugated potential that moves with a velocity given by the product of the external field rotation frequency and the videotape wavelength. This travelling grating provides a new method of manipulation as cold atoms are transported across the surface by surfing along the moving wave. Two theoretical methods have been developed to predict the behaviour of atoms reflecting from these stationary, variable magnitude and moving corrugated potentials. A simple analytic theory provides excellent agreement for reflection from a stationary corrugated potential and gives good agreement when extended to the case of a travelling grating. A Monte Carlo simulation was also performed by brute force numeric integration of the equations of motion for atoms reflecting from all three corrugated potential cases. Received: 1 December 1999 / Revised version: 3 February 2000 / Published online: 5 April 2000     

Reflection of a slow cesium atomic beam from a naturally magnetized Nd-Fe-B surface

We have demonstrated the partly directed reflection of a slow cesium atomic beam by using the natural magnetic stray field above a Nd-Fe-B surface. From these experiments we determine the reflectivity and a minimum value for the magnetic stray field directly at the surface. Received: 5 July 1999 / Revised version: 6 October 1999 / Published online: 3 November 1999     

Electrostatic guiding of cold polar molecules on a chip

We propose a novel scheme to guide cold polar molecules on the surface of an insulating substrate (i.e. a chip) using an electrostatic field generated by the combination of a pair of parallel charged wires and a grounded metal plate. The spatial distributions of the electric fields from the above charged-wire layout and their Stark potentials for cold CO molecules and dipole forces are calculated, and the relationships between the electric field and the geometric parameters of our charged-wire system are analyzed. Our study shows that our charged-wire scheme can be used to guide cold polar molecules in the weak-field-seeking state, and to construct various molecular optical elements, such as a molecular funnel, a molecular beam splitter and a molecular interferometer and so on, to form various integrated molecular optical elements and their molecular chips, and even to generate a continuous wave (CW) cold molecular beam by using a low-pass energy filter based on bent two-wire guiding.     

Optical traps for quantum gases

Received: 19 June 1998     

A neutral atom and a wire: towards mesoscopic atom optics

A large variety of trapping and guiding potentials can be designed by bringing cold atoms close to charged or current-carrying material objects. Using a current-carrying wire we demonstrate how to build guides and traps for neutral atoms and using a charged wire we study a 1/r ² singularity. The simplicity and versatility of the principles demonstrated in our experiments will allow for miniaturization and integration of atom optical elements into matter-wave quantum circuits. Received: 13 December 1998 / Revised version: 8 July 1999 / Published online: 8 September 1999     

Micromanipulation of neutral atoms with nanofabricated structures

A large variety of trapping and guiding potentials can be designed by bringing cold atoms close to charged or current carrying material objects. We describe the basic principles of constructing microscopic traps and guides and how to load atoms into them. The simplicity and versatility of these methods will allow for miniaturization and integration of atom optical elements into matter-wave quantum circuits on Atom Chips. These could form the basis for robust and widespread applications in atom optics, ranging from fundamental studies in mesoscopic physics to possibly quantum information systems. Received: 20 December 1999 / Revised version: 7 March 2000 / Published online: 5 April 2000     

Electrostatic Surface Trap for Cold Polar Molecules with a Charged Circular Wire

We propose a novel scheme to trap cold polar molecules on the surface of an insulating substrate （i.e. a chip） by using an inhomogeneous electrostatic field, which is generated by the combination of a circular charged wire （a ring electrode） and a grounded metal plate. The spatial distributions of the electrostatic field from the above charged wire layout and its Stark potentials for CO molecules are calculated. Our study shows that when the voltage applied to the wire is U = 15 kV, a ring radius is R = 5 mm, the thickness of the insulating substrate is b = 5 mm, and a wire radius is r = 1mm, the maximum efficient trapping potential （i.e., as equivalent temperature） for CO molecules is greater than 141.7mK, which is high enough to trap cold polar molecules with a temperature of 50 mK in the low-field-seeking states.     

An Enriched ^40K Source for Atomic Cooling

We have developed an enriched ⁴⁰K source used in ⁴⁰K--⁸⁷Rb atomic mixture cooling experiment. The enriched ⁴⁰K source is a home-made dispenser which releases ⁴⁰K atoms by the redox reaction between ⁴⁰K enriched KCl and calcium. It is efficient and easy to be made and used. We collect 10⁷ ～10^{8 40}K atoms in collection magneto-optical trap. With this dispenser, we perform a quantum degenerate Fermi gas experiment.     

A New Desirable Molecular Species for Stark Deceleration

We demonstrate a new molecular sample （CH radical） for Stark deceleration by Monte Carlo simulation, study the dependences of the decelerating effect on the different phase angles, stage number and decelerating voltages, and obtain some new optimized conditions and parameters. We also calculate the Stark energy shift of different quantum states of CH radical in the Stark decelerator electrostatic field and their populations in a supersonic CH molecular beam. Our study shows that the mean velocity of the supersonic CH molecular beam in the 2^∏1/2 state can be decelerated from 380 m/s to 24 m/s, and the corresponding translation temperature is lowered from 2.8 K to 27mK. It is thus clear that the CH radical is a new and desirable candidate for Stark deceleration.     

Atom lithography with a cold, metastable neon beam

We study different aspects of atom lithography with metastable neon atoms. Proximity printing of stencil masks is used to test suitable resists that are sensitive to the internal energy of the atoms, including dodecanethiols on gold and octadecyltrichlorosilanes grown on a SiO₂ surface. As an example of patterning the atomic beam with laser light, we create parallel line structures on the surface with a periodicity of half the laser wavelength by locally de-exciting the atoms in a standing quenching wave. Received: 29 June 1999 / Revised version: 30 August 1999 / Published online: 10 November 1999     

Laser spectroscopy on molecular beam with a time-of-flight mass spectrometer operating in a strong magnetic field

Experimental set-up for studying effects of a strong magnetic field on a structure and a decay dynamics of molecules, was designed and constructed. A vacuum chamber, in which a molecular beam propagated, was mounted in a bore of a superconducting magnet. Laser light crossed the molecular beam in the magnetic field and excited the molecules. Fragment or parent ions produced through sequential decay processes, were extracted by an electric field parallel to the magnetic field and detected by a microchannel plate. By measuring the time-of-flight from the photo-excitation to the ion-detection, a species of ions —mass and charge state— was identified. A performance of the set-up was demonstrated using the resonance enhanced multiphoton ionization process through the X²Π-A²Σ⁺ transition of nitric oxide (NO) molecules. A mass resolution m/Δm ≥180±6 was obtained in the field up to 10 T. This was the first successful result demonstrating the sufficient mass resolution obtained by the time-of-flight technique in the strong magnetic field up to 10 T. Parent NO⁺ ions were selectively detected by the mass spectrometer and the ion current was measured as a function of the frequency of the laser light. Rotational transition lines were measured with a sufficient S/N ratio in the field up to 10 T.     

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     

Magneto-optical trap and mass-separator system for the ultra-sensitive detection of <Superscript>135</Superscript>Cs and <Superscript>137</Superscript>Cs

We report the first magneto-optical trapping of radioactive ¹³⁵Cs and ¹³⁷Cs and a promising means for detecting these isotopes at ultra-sensitive levels by coupling a magneto-optical trap (MOT) to a mass separator. A sample containing both isotopes was placed in the source of a mass separator, ionized, mass-separated, and implanted in a Zr foil within the trapping cell. After implantation, atoms were released from the foil by inductive heating and then captured in a MOT that used large-diameter beams and a dry-film-coated cell to achieve high trapping efficiency. Trapped-atom numbers in the case of either isotope ranged from 10⁴ to 10⁷, as determined from the MOT fluorescence signal. Over this trapped-atom range, the MOT fluorescence signal was found to increase linearly with the number of atoms implanted in the foil and without isotopic bias to within 4%. In principle, this method can then provide a measurement of the ¹³⁷Cs/¹³⁵Cs ratio accurate to within 4% through the direct ratio of MOT fluorescence signals. The fluorescence signal from stable ¹³³Cs, when implanted and released from the foil, was suppressed relative to MOT signals by more than seven orders of magnitude when the system was tuned to trap ¹³⁵Cs or ¹³⁷Cs. When combined with the isotopic selectivity of ≥10⁵ for the mass separator, the overall suppression of ¹³³Cs is expected to exceed 10¹². At present our system delivers atoms from sample to MOT with an efficiency of 0.5%, has a trapped-atom detection limit of 4000 atoms, and achieves a sample-detection sensitivity of one million atoms. Received: 23 August 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +1-505/667-0440, E-mail: mdd@lanl.gov     

High Performance Small Optically Pumped Caesium Beam Frequency Standard

An experiment of a high performance small optically pumped caesium （Cs） beam frequency standard is reported. An extended cavity diode laser works as the probing laser, of which the frequency is stabilized by the Zeeman modulation method. The running parameters of the frequency standard are dynamically optimized via digital servo electronics. The experimental setup improves the frequency stability up to 1.8 × 10^-12 at T = 1 s and about 1.0 × 10^-13 at T= 10^5s （Allan deviation）     

Experimental Study on Electrostatic with Two Guiding of Supersonic D20 Molecular Beam Charged Wires

We demonstrate the guiding of a supersonic heavy-water （D2O） molecular beam using a hollow electrostatic field generated by the combination of two parallel charged-wires and two grounded metal-plates, and report some new and preliminary experimental results. In the experiment, we detect the guiding signals by using the method of time-of-flight mass spectrum and study the dependence of the relative transmission of the beam guide on the guiding voltage. Our study shows that the relative transmission of the beam guide is increased linearly with increasing guiding voltage Vguid, and the number of the guided D20 molecules is at least increased by 89.4% when the guiding voltage is ＋20.0k V. Finally, some potential applications of our guiding scheme in the molecule optics are briefly discussed.     

A 2-dimensional detector with high spatial and temporal resolution for metastable rare gas atoms

We describe a detector for metastable rare gas atoms which allows the investigation of transverse atomic beam distributions on the single atom level with lateral dimensions of 1 m, which occur frequently in the field of atom optics. In contrast to existing detection techniques, the conversion step from the metastable atom to an electron is separated from the charge amplification to improve spatial resolution. The conversion is performed at a metal surface, which is followed by an electron-optical system imaging the electron distribution with a proper magnification onto a single electron detection unit. The spatial resolution that we achieve with this technique is on the order of 1 m, the temporal resolution on the order of 1 s. The application of the detector for atom interferometry is discussed. Received: 22 May 1996 / Revised version: 21 June 1996     

High harmonic generation at 1 kHz repetition rate with a pulsed valve

High harmonic generation at 1 kHz repetition rate is reported. A piezoelectric pulsed valve together with a femtosecond Ti:Sapphire laser both operating at 1 kHz are employed to generate high harmonic radiation in xenon and argon. The characteristics of the valve have been analyzed by using a fast ion gauge and a time-of-flight mass-spectrometer. Received: 28 May 2001 / Revised version: 29 June 2001 / Published online: 18 July 2001     

Fragmentation of dodecanethiol molecules: application to self-assembled monolayer damage in atom lithography

Atom lithography commonly employs self-assem- bled monolayers (SAMs) of alkanethiols which act as resists to protect prepared surfaces. Metastable atomic species such as helium are used to damage the resist, enabling pattern transfer via mask lithography, followed by wet chemical etching. The damage mechanism is, however, not well understood. Here we report studies of fragmentation of dodecanethiol (DDT) molecules embedded in helium nano-droplets that have been irradiated by an electron beam. The results of the charge-transfer fragmentation process provide the first experimental data on the damage mechanisms that occur in the metastable helium/SAM interaction. Received: 20 September 1999 / Revised version: 6 December 1999 / Published online: 8 March 2000