van Kah Ton Leeuwen

Observation of Nonspreading Wave Packets in an Imaginary Potential

We propose and experimentally demonstrate a method to prepare a nonspreading atomic wave packet. Our technique relies on a spatially modulated absorption constantly chiseling away from an initially broad de Broglie wave. The resulting contraction is balanced by dispersion due to Heisenbergs uncertainty principle. This quantum evolution results in the formation of a nonspreading wave packet of Gaussian form with a spatially quadratic phase. Experimentally, we confirm these predictions by observing the evolution of the momentum distribution. Moreover, by employing interferometric techniques, we measure the predicted quadratic phase across the wave packet. Nonspreading wave packets of this kind also exist in two space dimensions and we can control their amplitude and phase using optical elements.

Atom lithography of Fe

Direct write atom lithography is a technique in which nearly resonant light is used to pattern an atom beam. Nanostructures are formed when the patterned beam falls onto a substrate. We have applied this lithography scheme to a ferromagnetic element, using a 372nm laser light standing wave to pattern a beam of iron atoms. In this proof-of-principle experiment, we have deposited a grid of 50-nm-wide lines 186nm apart. These ultraregular, large-scale, ferromagnetic wire arrays may generate exciting new developments in the fields of spintronics and nanomagnetics.

Progress towards atom lithography on iron

We aim to apply atom optical techniques to iron to produce periodic magnetic nanostructures. Laser cooling has been observed experimentally, and calculations predict that a bright beam can be obtained with 200 µrad divergence. We expect to be able to laser focus this beam to feature sizes around 10 nm by the use of nanoseale mechanical beam masking and velocity selection via a supersonic source. In separate calculations, we have modelled surface diffusion of the atoms during deposition using a kinetic Monte Carlo approach taking into account the Ehrlich-Schwoebel barrier. These calculations successfully explain anomalous broadening of structures observed in similar experiments on chromium [Anderson et al., Phys. Rev. A 59 (1999) 2476].

Barrier-limited surface diffusion in atom lithography

Thermally activated surface diffusion has a strong influence on structure widths in atom lithography. We investigate the effects of two barriers to thermally activated atomic diffusion on atom lithography: a thermally activated Ehrlich–Schwoebel (ES) barrier, and pollution from the residual gas in the vacuum system. We performed kinetic Monte Carlo simulations using a one-dimensional surface grid. We find that the ES barrier fails to explain the lack of temperature dependence observed experimentally [W. R. Anderson et al., Phys. Rev. A 59, 2476 (1999)]. The dependencies of the structure width on temperature, vacuum conditions, and beam characteristics can be explained using the pollutant adatom hypothesis. Only the variation of structure width with deposition duration was not entirely reproduced by this model. We attribute this to the one-dimensional nature of our simulations. These results demonstrate that barrier-limited diffusion can play an important role in atom lithography, and that pollutant adatom...

Laser cooling and trapping visualized

Laser cooling and trapping have become widely used in the atomic physics laboratory. A computer program is presented that simulates some of the most important techniques employed, including atomic beam collimation, Zeeman slowing, funneling, and magneto-optical trapping. Its application ranges from experiment design to illustration of course material.

Booster for ultra-fast loading of atom traps

Abstract We propose a 2D magneto-optical compressor with a very large 40 mm diameter acceptance area to funnel the low velocity tail of the Maxwell–Boltzmann distribution ( v ≤100 m/s) in a low pressure discharge (Ne * ) or alkali vapor cell (Na) into a well-collimated (10 mrad) bright beam of 10 7 to 10 8 atoms/s for Ne * or 2×10 11 atoms/s for Na, leaving the cell through a 1 mm orifice. After axial cooling in an isotropic light field, resulting in an axial velocity distribution with 〈 v 〉=8 m/s with a FWHM Δ v =3 m/s, this beam can be efficiently loaded into an atom trap. For rubidium, the predicted flux is 8×10 11 atoms/s. Compared to all other alkali vapor-cell schemes, the gain in loading rate is a factor of 20 to 100, a major boost for achieving Bose–Einstein condensation. For the metastable rare gas atoms, it is the first table-top scheme for experiments with atom traps.

Atomic quasi-Bragg-diffraction in a magnetic field

We report on a technique to split an at. beam coherently with an easily adjustable splitting angle. In our expt. metastable helium atoms in the |{1s2s}3S1 M=1 state diffract from a polarization gradient light field formed by counterpropagating .sigma.+ and .sigma.- polarized laser beams in the presence of a homogeneous magnetic field. In the near-adiabatic regime, energy conservation allows the resonant exchange between magnetic energy and kinetic energy. As a consequence, sym. diffraction of |M=0 or |M=-1 atoms in a single order is achieved, where the order can be chosen freely by tuning the magnetic field. We present exptl. results up to sixth-order diffraction (24[planck]k momentum splitting, i.e., 2.21 m/s in transverse velocity) and present a simple theor. model that stresses the similarity with conventional Bragg scattering. The resulting device constitutes a flexible, adjustable, large-angle, three-way coherent at. beam splitter with many potential applications in atom optics and atom interferometry.