Table of contents

This conference, held at Internationales Wissenschaftsforum, Heidelberg, Germany, from 4-8 April 2005, brought together physicists, chemists, and surface scientists from around the world to discuss advances in our understanding of how atoms and molecules interact with each other and with applied fields when they are near surfaces. The fields include static magnetic and electric fields as well as electromagnetic fields in the optical frequency range. This understanding is, of course, essential for the controlled manipulation of matter at the atomic scale by micro- and nanostructured devices. Several principal themes motivate the efforts of this interdisciplinary community: the fundamental physics of quantum degenerate gases near surfaces, the realisation of `atom chips' for the construction of quantum information gates and registers, the development of integrated `on chip' sources providing atoms on demand, the ability to control precision doping, at the atomic level, new molecular spectroscopies appearing under reduced dimensionality imposed by surfaces, and advances in STM and AFM `bottom up' construction of functional devices, starting from the fundamental atom building block. What follows here are the written CAMS proceedings based on the presentations, oral and poster, of the research pursued by the various participating groups.

CAMS was organised and supported by FASTNet, Field-Atom-Surface Training Network, a 5th Framework Research and Training Network of the European Union. A sister network, ATOMCHIPS, also participated in the financial and scientific support of the conference. The CAMS workshop emphasised the participation of the young scientists, post-docs and pre-docs of the two networks. In addition financial support from the European Science Foundation is gratefully acknowledged.

The conference was held at the Internationales Wissenschaftsforum of the Ruprecht-Karls-Universität Heidelberg. The excellent facilities and the competent support of the professional staff, headed by Dr Theresa Reiter, managing director, created a genial environment for scientific discussion and exchange. Their invaluable assistance is also gratefully acknowledged.

Studies of the long-range interactions between cold atoms and surfaces are now of vital interest. The interest is partly driven by nanotechnology applications, partly by the exploding interest in the encompassing superfield of Casimir effects, and partly by the burgeoning overlap between atomic and molecular physics, condensed matter, and quantum optics. This tutorial lecture will address long-range atom-surface interactions for cold atoms, including an overview of Casimir-Polder interactions and their various manifestations. Some previous theoretical studies that are of particular relevance will be reviewed. In addition some different approaches to the problem and corresponding results, especially concerning the effects of substrate composition, geometry, and finite temperature, will be discussed.

The dynamics of atom/molecule scattering at surfaces plays a crucial role in such diverse applications as heterogeneous catalysis, chemical vapor deposition and aerodynamics. This process traditionally has been investigated with the use of atomic/molecular beams under ultra-high-vacuum conditions, i.e. far from the regime required in applications that has been formulated as a 'pressure gap' problem. The advantages of laser spectroscopy, however, suggest a principally new approach to this dilemma.

In this paper we present recent results, both experimentally and theoretically, illustrating the potential of evanescent wave spectroscopy for surface science. We demonstrate how such fundamental features of gas-surface scattering as the scattering kernel, sticking probability and velocity distribution functions can be extracted from a careful analysis of nonlinear fluorescence spectra excited by both evanescent and non-evanescent waves. We also review the prospective developments of this technique which are based on a four-wave mixing process and Raman scattering in atoms/molecules near surfaces.

Since the recent realization of extremely thin vapour cells (local thickness: 20-1000 nm), we investigate the optical properties of these 1-D confined vapours. Aside from their interest for Doppler-free spectroscopy, nanocells offer a new tool to evaluate collisional shift and broadening, yielding an access to the open problem of collisions under confinement. It also allows probing of the atom-surface interaction in a range of unusual short distances. The experimental exploration of the distance dependence, normally evolving according to the z⁻³ van der Waals (vW) dependence (z : the atom-surface distance), is worth doing because it could be affected by imperfections of the real surface, such as roughness, adsorbed impurities or charges. A detailed lineshape analysis is now under progress, with tight constraints imposed to the fitting by the twin information brought by simultaneous reflection and transmission spectra. Another issue is a possible resonant enhancement, susceptible to induce a repulsive vW, due to the coupling between atom excitation and a surface mode.

The magnetic trapping potentials for atoms on atom chips are determined by the current flow pattern in the chip wires. By modifying the wire shape using focused ion beam nano-machining we can design specialized current flow patterns and therefore micro-design the magnetic trapping potentials. We give designs for a barrier, a quantum dot, and a double well or double barrier and show preliminary experiments with ultra cold atoms in these designed potentials.

We give an overview on quantum electrodynamics (QED) with atoms located near a planar surface. Starting from basic concepts like electric and magnetic dipole transitions and electromagnetic near fields, we explain some properties of magnetic fields that are relevant for ultracold atoms in hybrid electromagnetic-surface traps. In particular, we discuss next order corrections to the atom-surface interaction potential due to the magnetic moment.

A method for obtaining a metastable atom beam with properties near to those of a ground state supersonic beam is demonstrated. Calculations on m sublevels of metastable argon near a metal surface are then presented.

We propose a method to focus a cloud of condensed atoms by imprinting a phase on the atomic wave function. The main goal of our experiment under construction is to study the conditions of realization of atomic holography or deposition in the nanometer range. This experiment will also investigate the role of the atom-atom interactions in these processes.

Four atom optics experiments that each serve to measure atom-surface interactions near nanofabricated gratings are presented here. In these experiments atoms in a beam travel within 25 nm of a material grating bar, and the analysis incorporates phase shifts for the atomic de Broglie waves due to interactions betwen Na atoms and silicon nitride surfaces. One atom diffraction experiment determines the van der Waals coeficient C₃ = 2.7 ± 0.8 meV nm³, and one atom interferometer experiment determines C₃ = 4 ± 1 meV nm³. The results of all four experiments are consistent with the Lifshitz prediction that is explicitly calculated here for Nasilicon nitride to be C₃ = 3.25 meV nm³. The four atom optics experiments and review of van der Waals theory are complemented by similar experiments using electron beams and analysis of image-charge effects.

Microscopic atom optical devices integrated on atom chips allow to precisely control and manipulate ultra-cold (T < 1 µK) neutral atoms and Bose-Einstein condensates (BECs) close to surfaces. The relevant energy scale of a BEC is extremely small (down to < 10⁻¹¹ eV). Consequently, BECs can be utilized as a sensor for variations of the potential energy of the atoms close to the surface. Here we describe how to use trapped atoms as a measurement device and analyze the performance and flexibility of the field sensor. We demonstrate microscopic magnetic imaging with simultaneous high spatial resolution (3 µm) and high field sensitivity (4 nT). With one dimensional BECs, we probe the magnetic field variations close to the surface at distances down to a few microns. Measurements of the magnetic field of a 100 µm wide current carrying wire imply that the magnetic field variations stem from residual variations of the current flow direction, resulting from local properties of the wire. These disorder potentials found near lithographically fabricated wires are two orders of magnitude smaller than those measured close to electroplated conductors.

In this paper we will report on four experiments which have been carried out in the last year in our group. All of these experiments are necessary steps towards the trapping and probing of ultracold molecules on a chip surface.

Atom-chip technology can be used to confine atoms tightly using permanently magnetised videotape along with external magnetic fields. The one-dimensional (1D) gas regime can be realised and studied by trapping the atoms in high-aspect-ratio traps in which the radial motion of the system is confined to zero-point oscillation.

We describe an atom chip based on periodically magnetised videotape. Cold atoms are loaded into one of the microscopic magnetic traps formed by the videotape atom chip. Using forced evaporation we have produced a ⁸⁷Rb Bose–Einstein condensate in a permanent-magnet microtrap.

Light-induced desorption and diffusion of alkali atoms embedded in dielectric substrates are experimentally and theoretically investigated. The goal is to realize atomic dispensers fully controlled by light, to study the atom-dielectric interaction and to make spectroscopy of atoms confined in micro-nano structures. Very interesting results have been obtained with Rb and Cs in PDMS films and porous glasses.

Recently we observed non-thermal photoejection of atoms embedded in nano-porous silica samples. Alkali atoms are stored inside porous glass matrices and then they are desorbed by ordinary or laser light. In this paper, we present an experimental investigation of the dependence of photodesorption dynamics on desorbing radiation, showing that light induced effects on alkali nano-particles, dispersed in the glass matrix, are started up upon specific conditions of the incident radiation. On the basis of this study, we find that the light is able both to drive the atomic flux from the glass surface and to modify the optical properties of the glass samples, opening interesting perspectives for applications.

We observe Light-induced atomic desorption (LIAD) of Rb and Cs atoms from a PDMS-coated cell containing both atoms at the same time. The desorption rate and the relative vapor density variation have been simultaneously measured for both alkali atoms as a function of the desorbing light intensity and frequency. They show the same behaviour upon the different illumination conditions. This work demonstrates the possibility to provide light controlled atomic dispenser delivering different atomic species using the LIAD effect.

A combination of a large scaled 'carrier chip' and micron scaled 'atom-optics chips' is used for phase coherent manipulation Bose–Einstein condensates. Diffraction of condensates from a magnetic lattice potential is observed up to the fifth order.

We present experiments with cold atoms in optical dipole potentials which are directed towards developing an integrated coherent atom optics with micro-optical systems. We describe an experiment on evaporative cooling in a far-detuned optical dipole trap for ⁸⁷Rb. The dipole trap is created by a solid state laser at a wavelength of 1030 nm. To achieve high initial phase space densities allowing for efficient evaporative cooling, we have optimised the loading process from a magneto-optical trap into the dipole trap. Starting with an initial phase space density of 2 × 10⁻⁴ the trap depth was ramped down and temperatures below 200 nK and phase space densities of about 0.2 could be reached. These investigations aim at the creation of an 'all-optical' BEC based on a simple experimental scheme. As an example for an integrated atom optical system, we present the transport of atoms in a ring-shaped guiding structure, i.e. optical storage ring, for cold atoms which is produced by a micro-fabricated ring lens.

We present the results of experiments in support of the composite diffracted evanescent wave (CDEW) model that describes the response of subwavelength planar structures to illumination by polarised plane-wave optical excitation. These experiments consist of four types of data: (1) angular distribution of the transmitted light as a function of quarterwave groove displacement, (2) efficiency of transmission through a subwavelength slit as a function of slit-groove distance, (3) relative phase measurements by far-field interference patterns of transmitted light as a function of slit-groove displacement, and (4) far-field spatial profile of the optical field intensity issuing from subwavelength slits flanked by periodic grooves and fabricated on a thin metallic layer. These types of structure are of interest for the manipulation of cold atoms by optical potentials near surfaces.

We report the results of a study into the quality of functionalized surfaces for nanolithographic imaging. Self-assembled monolayer (SAM) coverage, subsequent post-etch pattern definition and minimum feature size all depend on the quality of the Au substrate used in atomic nanolithographic experiments. We find sputtered Au substrates yield much smoother surfaces and a higher density of {111} oriented grains than evaporated Au surfaces. A detailed study of the self-assembly mechanism using molecular resolution AFM and STM has shown that the monolayer is composed of domains with sizes typically of 5-25 nm, and multiple molecular domains can exist within one Au grain. Exposure of the SAM to an optically-cooled atomic Cs beam traversing a two-dimensional array of submicron material masks ans also standing wave optical masks allowed determination of the minimum average Cs dose (2 Cs atoms per SAM molecule) and the realization of < 50 nm structures. The SAM monolayer contains many non-uniformities such as pin-holes, domain boundaries and monoatomic depressions which are present in the Au surface prior to SAM adsorption. These imperfections limit the use of alkanethiols as a resist in atomic nanolithography experiments. These studies have allowed us to realize an Atom Pencil suitable for deposition of precision quantities of material at the microand nanoscale to an active surface.

Recent advances in atomic nanofabrication with laser manipulated atomic beams are discussed with regard to the creation of arbitrary structures.

Matter-wave interferometry with large molecules is partially limited by the inefficiency of the commonly used ionization detection schemes. Here we discuss the possibility of employing a surface imaging method in which molecular interferograms with periods in the micron range are adsorbed on a surface and subsequently read using fluorescence microscopy. Our preliminary experiments show that the detection efficiency can be significantly increased compared to electron impact ionization and quadrupole mass spectrometry. However the interpretation of fluorescent molecular patterns requires a good understanding and control of the molecular mobility, the bleaching behavior, and the coverage dependence of the fluorescence intensity.

We consider a time-dependent atom interferometer based on splitting and merging an elongated Bose-Einstein condensate (BEC) along the weakly bound axis. The interference phase is imprinted at maximum splitting, and both arms are then recombined. We discuss a framework to include thermally populated low-energy excitations. Previous studies performed at zero temperature in the mean field description are extended using a truncated Wigner method. First results are discussed for the dipole mode oscillations in the recombined trapping potential.

We present recent results on atom optics with Bose–Einstein condensates obtained at MIT. These results demonstrate the flexibility of micro-fabricated atom traps (atom-chips) and the interaction of Bose–Einstein condensates with surfaces through normal incidence quantum reflection.

The interaction of Na atoms with a surface was probed by inserting a nanofabricated material grating into one arm of an atom interferometer (IFM). This technique permits a direct measurement of the change in phase and coherence of matter waves as they pass within 25 nm of the grating bar surface. The practical concerns and challenges of making such a measurement are discussed here. Interference of spurious diffraction orders, IFM path overlap, and the partial obscuration of IFM beams are all important aspects of this experiment. The systematic effects that contribute to the measured phase shift and contrast are discussed.

We present experimental results and theoretical analysis of the diffuse reflection of a Bose–Einstein condensate from a rough mirror. The mirror is produced by a blue-detuned evanescent wave supported by a dielectric substrate. The results are carefully analysed via a comparison with a numerical simulation. The scattering is clearly anisotropic, more pronounced in the direction of the evanescent wave surface propagation, as predicted theoretically.

The coherent reflection of ultra-cold neon and helium atoms from silicon surfaces and surface structures is measured and analyzed. When the silicon surface is flat, the reflection is explained by the quantum reflection due to van der Waals attractive potential near the silicon surface. When the silicon surface is modified to form a grating structure, the reflectivity increases dramatically. For certain ranges of surface structure parameters, the reflection may be interpreted as a coherent summation of Fresnel diffraction of the atomic wave at the ridges of the grating structure.

So far, most of the high resolution scanning probe microscopy studies of organic molecules were restricted to metallic substrates. Insulating substrates are mandatory when the molecules need to be electrically decoupled in a electronic circuit. In such a case, atomic force microscopy is required. In this paper we will discuss our recent studies on different organic molecules deposited on KBr surfaces in ultra-high vacuum, and then imaged by AFM at room temperature. The distance between tip and surface was controlled either by the frequency-shift of the cantilever resonance or by the excitation signal required to keep the oscillation amplitude constant. Advantages and drawbacks of both techniques are discussed. The high mobility of the molecules, due to their weak interaction with the substrate, hinders the formation of regular self assembled structures. To overcome this problem we created artificial structures on the surface by annealing and by electron irradiation, which made possible the growth of the molecules onto step edges and their confinement into rectangular pits.

Initially invented to image surfaces down to atomic scale, the scanning tunneling microscope (STM) has been further developed in the last few years to an operative tool, with which atoms and molecules can be manipulated at low substrate temperatures at will with atomic precision in different manners by using solely the tip-adparticle forces. In this way various artificial structures on naoscale have been created and in situ characterized with the STM. Such structures as well as single molecules can be investigated by scanning tunnelling spectroscopy (STS) both with respect to their local electronic and even vibrational properties. Modifications of single molecules can be induced by using the tunnelling electron current: Rotations, diffusional jumps, vibrational excitations, desorption, dissociation and even association can be induced in individual molecules, often in a rather precise way by tuning the voltage into the energy levels of specific vibrations or electronic levels. These possibilities give rise to startling new opportunities for physical and chemical experiments on the single atom and single molecule level. Here a brief overview on results obtained with these new techniques is given.

The growth of Ni thin film on the Cu(100) surface at 280 K has been studied by means of thermal-energy helium atom scattering. A near layer-by-layer growth is observed below ∼7 ML followed by a multilayer structure at higher coverages. Spot profile analysis shows Ni islands transfer from irregular shape to square with increasing Ni coverage. The mean island separation is measured as a function of coverage. The 0.5 ML Ni/Cu(100) surface turns out to be an ideal prototype, nano-structured surface for future interference measurements.

We review recent experimental studies of spin polarized atomic hydrogen gas adsorbed on the surface of liquid helium.