We study the widths of interspecies Feshbach resonances in a mixture of the fermionic quantum gases 6Li and 40K. We develop a model to calculate the width and position of all available Feshbach resonances for a system. Using the model, we select the optimal resonance to study the {6}Li/{40}K mixture. Experimentally, we obtain the asymmetric Fano line shape of the interspecies elastic cross section by measuring the distillation rate of 6Li atoms from a potassium-rich 6Li/{40}K mixture as a function of magnetic field. This provides us with the first experimental determination of the width of a resonance in this mixture, DeltaB=1.5(5) G. Our results offer good perspectives for the observation of universal crossover physics using this mass-imbalanced fermionic mixture.

We demonstrate a novel 2D MOT beam source for cold 6 Li atoms. The source is side-loaded from an oven operated at temperatures in the range 600 T 700 K. The performance is analyzed by loading the atoms into a 3D MOT located 220 mm downstream from the source. The maximum recapture rate of ∼ 10 9 s −1 is obtained for T ≈ 700 K and results in a total of up to 10 10 trapped atoms. The recaptured fraction is estimated to be 30 ± 10% and limited by beam divergence. The most-probable velocity in the beam (αz) is varied from 18 to 70 m/s by increasing the intensity of a push beam. The source is quite monochromatic with a full-width at half maximum velocity spread of 11 m/s at αz = 36 m/s, demonstrating that side-loading completely eliminates beam contamination by hot vapor from the oven. We identify depletion of the low-velocity tail of the oven flux as the limiting loss mechanism. Our approach is suitable for other atomic species.

We report on the observation of Bragg scattering at 1D atomic lattices. Cold atoms are confined by optical dipole forces at the antinodes of a standing wave generated by the two counter-propagating modes of a laser-driven high-finesse ring cavity. By heterodyning the Bragg-scattered light with a reference beam, we obtain detailed information on phase shifts imparted by the Bragg scattering process. Being deep in the Lamb-Dicke regime, the scattered light is not broadened by the motion of individual atoms. In contrast, we have detected signatures of global translatory motion of the atomic grating.PACS numbers: 42.50. Vk, 05.45.Xt, 05.65+b, 05.70.Fh Elastic Rayleigh scattering is a phase-coherent process. In thermal atomic clouds however the photonic recoil transferred to the atoms by the scattering process introduces inhomogeneous line broadening washing out the phase-coherence. Furthermore, Rayleigh scattering only dominates at small intensities; stronger pumping causes power broadening, which merely increases the inelastic components of the resonance fluorescence. For these reasons it is difficult to directly measure the phase-shift induced by Rayleigh scattering.A phase-coherent study of Rayleigh scattering is facilitated by two measures: 1. Using cold and strongly confined atoms, and 2. arranging for long-range order in the atomic cloud. By cooling the atoms the Dopplerbroadening is reduced; by tightly confining them within a very small region of space, i.e. within the Lamb-Dicke limit, no recoil is imparted to individual atoms; and by creating density gratings the elastic part of the resonance fluorescence is concentrated into a very small solid angle. The resonant enhancement of the structure factor for elastic Rayleigh scattering by atomic long-range order is called Bragg scattering.Periodic structures are generally probed by Bragg scattering. A probe beam is shone onto the sample under a certain angle, the so-called Bragg angle, and the emergence of phase-coherent light at well-defined sharp solid angles is a signature of long-range order. This procedure can be applied to periodic arrangements of atoms in optical gratings. Bragg scattering of light at 3D atomic lattices has for the first time been observed by Birkl et al. and Weidemüller et al. [1,2].The elastic peak of the atomic response to incident laser light has been observed in several experiments. Westbrook et al. [3,4] used the heterodyne method to beat down the fluorescence of magneto-optically trapped atoms with a local oscillator to electronically accessible frequencies. It is in principle possible to probe the complete fluorescence spectrum, i.e. the Mollow triplet and the elastic Rayleigh peak by scanning the reference laser. This technique permitted Westbrook et al. to detect Dicke-narrowing of Rayleigh scattering in magnetooptical traps. However in this experiment the heterodyne signal was integrated over long times, so that the phasecoherence of the elastic scattering process is not directly shown.We report here the first detailed phas...

We study Bragg scattering at one-dimensional ͑1D͒ optical lattices. Cold atoms are confined by the optical dipole force at the antinodes of a standing wave generated inside a laser-driven high-finesse cavity. The atoms arrange themselves into a chain of pancake-shaped layers located at the antinodes of the standing wave. Laser light incident on this chain is partially Bragg reflected. We observe an angular dependence of this Bragg reflection which is different from what is known from crystalline solids. In solids, the scattering layers can be taken to be infinitely spread ͑three-dimensional limit͒. This is not generally true for an optical lattice consistent of a 1D linear chain of pointlike scattering sites. By an explicit structure factor calculation, we derive a generalized Bragg condition, which is valid in the intermediate regime. This enables us to determine the aspect ratio of the atomic lattice from the angular dependance of the Bragg scattered light.

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