We study the population dynamics of a Bose-Einstein condensate in a double-well potential throughout the crossover from Josephson dynamics to hydrodynamics. At barriers higher than the chemical potential, we observe slow oscillations well described by a Josephson model. In the limit of low barriers, the fundamental frequency agrees with a simple hydrodynamic model, but we also observe a second, higher frequency. A full numerical simulation of the Gross-Pitaevskii equation giving the frequencies and amplitudes of the observed modes between these two limits is compared to the data and is used to understand the origin of the higher mode. Implications for trapped matter-wave interferometers are discussed.

Neutral fermions present new opportunities for testing many-body condensed matter systems, realizing precision atom interferometry, producing ultra-cold molecules, and investigating fundamental forces. However, since their first observation, quantum degenerate Fermi gases (DFGs) have continued to be challenging to produce, and have been realized in only a handful of laboratories. In this Letter, we report the production of a DFG using a simple apparatus based on a microfabricated magnetic trap. Similar approaches applied to Bose-Einstein Condensation (BEC) of 87Rb have accelerated evaporative cooling and eliminated the need for multiple vacuum chambers. We demonstrate sympathetic cooling for the first time in a microtrap, and cool 40K to Fermi degeneracy in just six seconds -- faster than has been possible in conventional magnetic traps. To understand our sympathetic cooling trajectory, we measure the temperature dependence of the 40K-87Rb cross-section and observe its Ramsauer-Townsend reduction.Comment: 5 pages, 4 figures (v3: new collision data, improved atom number calibration, revised text, improved figures.

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Abstract. In this article we review our recent experiments with a 40 K-87 Rb mixture. We demonstrate rapid sympathetic cooling of a 40 K-87 Rb mixture to dual quantum degeneracy on an atom chip. We also provide details on efficient BEC production, species-selective magnetic confinement, and progress toward integration of an optical lattice with an atom chip. The efficiency of our evaporation allows us to reach dual degeneracy after just 6 s of evaporation -more rapidly than in conventional magnetic traps. When optimizing evaporative cooling for efficient evaporation of 87 Rb alone we achieve BEC after just 4 s of evaporation and an 8 s total cycle time.

Direct picosecond measurements of nonlinear refractive index change and nonlinear absorption in In0.530Al0.141Ga0.329As/In0.530Ga0.470As multiquantum wells in the range 1480–1550 nm are reported. Large low-threshold nonlinear index changes are found: Δn of up to 0.14 with figure of merit of 1.38 at a fluence of 116 μJ/cm2. The index-change-over-absorption figure of merit, F, is greater than unity over much of the spectrum, pointing to the prospective applicability of the materials studied to nonlinear switching devices.

The intensity-dependent response of nonlinear Bragg-periodic epitaxially-grown InGaAs-InAlGaAs-based optical elements is reported over a broad spectral range 1.3-1.6 m. Large changes in the transmittance and reflectance are observed as a function of incident power. Over most of this spectral region, the nonlinear response is dominated by the saturation of absorption. In the vicinity of 1.5 m, the optical elements exhibit fluence-dependent Bragg diffraction. For low incident powers, the indices of refraction of structures are uniform and no coherent scattering takes place. With increased incident power a Bragg grating appears, resulting in the emergence of a fluence-dependent stopband in the transmittance and reflectance spectra.

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