Transport of Bose-Einstein Condensates with Optical Tweezers

We have transported gaseous Bose-Einstein condensates over distances up to 44 cm. This was accomplished by trapping the condensate in the focus of an infrared laser and translating the location of the laser focus with controlled acceleration. Condensates of order 1 million atoms were moved into an auxiliary chamber and loaded into a magnetic trap formed by a Z-shaped wire. This transport technique avoids the optical and mechanical access constraints of conventional condensate experiments and creates many new scientific opportunities.Comment: 5 pages, 3 figure

Spatial separation in a thermal mixture of ultracold 174^{174}Yb and 87^{87}Rb atoms

We report on the observation of unusually strong interactions in a thermal mixture of ultracold atoms which cause a significant modification of the spatial distribution. A mixture of $^{87}$Rb and $^{174}$Yb with a temperature of a few $\mu$K is prepared in a hybrid trap consisting of a bichromatic optical potential superimposed on a magnetic trap. For suitable trap parameters and temperatures, a spatial separation of the two species is observed. We infer that the separation is driven by a large interaction strength between $^{174}$Yb and $^{87}$Rb accompanied by a large three-body recombination rate. Based on this assumption we have developed a diffusion model which reproduces our observations

Magnetoresistance Anisotropy of Polycrystalline Cobalt Films: Geometrical-Size- and Domain-Effects

The magnetoresistance (MR) of 10 nm to 200 nm thin polycrystalline Co-films, deposited on glass and insulating Si(100), is studied in fields up to 120 kOe, aligned along the three principal directions with respect to the current: longitudinal, transverse (in-plane), and polar (out-of-plane). At technical saturation, the anisotropic MR (AMR) in polar fields turns out to be up to twice as large as in transverse fields, which resembles the yet unexplained geometrical size-effect (GSE), previously reported for Ni- and Permalloy films. Upon increasing temperature, the polar and transverse AMR's are reduced by phonon-mediated sd-scattering, but their ratio, i.e. the GSE remains unchanged. Basing on Potters's theory [Phys.Rev.B 10, 4626(1974)], we associate the GSE with an anisotropic effect of the spin-orbit interaction on the sd-scattering of the minority spins due to a film texture. Below magnetic saturation, the magnitudes and signs of all three MR's depend significantly on the domain structures depicted by magnetic force microscopy. Based on hysteresis loops and taking into account the GSE within an effective medium approach, the three MR's are explained by the different magnetization processes in the domain states. These reveal the importance of in-plane uniaxial anisotropy and out-of-plane texture for the thinnest and thickest films, respectively.Comment: 10 pages, 9 figure

Controlled Generation of Dark Solitons with Phase Imprinting

The generation of dark solitons in Bose-Einstein condensates with phase imprinting is studied by mapping it into the classic problem of a damped driven pendulum. We provide simple but powerful schemes of designing the phase imprint for various desired outcomes. We derive a formula for the number of dark solitons generated by a given phase step, and also obtain results which explain experimental observations.Comment: 4pages, 4 figure

Topological vortex formation in a Bose-Einstein condensate

Vortices were imprinted in a Bose-Einstein condensate using topological phases. Sodium condensates held in a Ioffe-Pritchard magnetic trap were transformed from a non-rotating state to one with quantized circulation by adiabatically inverting the magnetic bias field along the trap axis. Using surface wave spectroscopy, the axial angular momentum per particle of the vortex states was found to be consistent with $2\hbar$ or $4\hbar$, depending on the hyperfine state of the condensate.Comment: 5 pages, 3 figure

Drag of superfluid current in bilayer Bose systems

An effect of nondissipative drag of a superfluid flow in a system of two Bose gases confined in two parallel quasi two-dimensional traps is studied. Using an approach based on introduction of density and phase operators we compute the drag current at zero and finite temperatures for arbitrary ratio of densities of the particles in the adjacent layers. We demonstrate that in a system of two ring-shape traps the "drag force" influences on the drag trap in the same way as an external magnetic flux influences on a superconducting ring. It allows to use the drag effect to control persistent current states in superfluids and opens a possibility for implementing a Bose analog of the superconducting Josephson flux qubit.Comment: 12 pages, 2 figures, new section is added, refs are adde

Determination of the s-wave Scattering Length of Chromium

We have measured the deca-triplet s-wave scattering length of the bosonic chromium isotopes $^{52}$Cr and $^{50}$Cr. From the time constants for cross-dimensional thermalization in atomic samples we have determined the magnitudes $|a(^{52}Cr)|=(170 \pm 39)a_0$ and $|a(^{50}Cr)|=(40 \pm 15)a_0$, where $a_0=0.053nm$. By measuring the rethermalization rate of $^{52}$Cr over a wide temperature range and comparing the temperature dependence with the effective-range theory and single-channel calculations, we have obtained strong evidence that the sign of $a(^{52}Cr)$ is positive. Rescaling our $^{52}$Cr model potential to $^{50}$Cr strongly suggests that $a(^{50}Cr)$ is positive, too.Comment: v3: corrected typo in y-axis scaling of Figs. 3 and