Atomic interaction effects in the superradiant light scattering from a Bose-Einstein condensate

We investigate the effects of the atomic interaction in the Superradiant Rayleigh scattering from a Bose-Einstein condensate driven by a far-detuned laser beam. We show that for a homogeneous atomic sample the atomic interaction has only a dispersive effect, whereas in the inhomogeneous case it may increase the decay of the matter-wave grating.Comment: 12 pages, 4 figures, presented to the XII International Laser Physics Workshop, August 24-29, Hamburg, to be published in Laser Physic

Granivory in a desert ecosystem: experimental evidence for indirect facilitation of ants by rodents

Journal ArticleTwo major groups of desert granivores, ants and rodents, coexist as permanent residents of local desert habitats in southwestern North America. At our Sonoran Desert study site, both of the major taxa exhibited short-term increase in density when the other taxon was experimentally removed. Over the longer term, density compensation continued at a relatively constant level for rodents in the absence of ants. In contrast, beginning about 2 years after initiation of experiments, ant populations on rodent removal plots showed a gradual but significant decline relative to densities on control plots. Indirect interactions, mediated through ant and rodent resources, may account for these differences. Removal of harvester ants leads to higher annual plant densities only in small-seeded species. These plants are relatively poor competitors and do not displace the large-seeded annuals, on whose seeds rodents specialize. In contrast, rodent removal leads to a differential increase in large-seeded annuals, which competitively displace the small-seeded resource species of ants. The decline of ant populations on rodent removal plots preceded by several years the first detectable evidence for competitive suppression of small-seeded annuals. Because ants do not excavate buried seed, they probably experienced resource depression before buried seed reserves were exhausted through germination and subsequent competitive inhibition

Does matter wave amplification work for fermions?

We discuss the relationship between bosonic stimulation, density fluctuations, and matter wave gratings. It is shown that enhanced stimulated scattering, matter wave amplification and atomic four-wave mixing are in principle possible for fermionic or non-degenerate samples if they are prepared in a cooperative state. In practice, there are limitations by short coherence times.Comment: 5 pages, 1 figure

Predicting and verifying transition strengths from weakly bound molecules

We investigated transition strengths from ultracold weakly bound 41K87Rb molecules produced via the photoassociation of laser-cooled atoms. An accurate potential energy curve of the excited state (3)1Sigma+ was constructed by carrying out direct potential fit analysis of rotational spectra obtained via depletion spectroscopy. Vibrational energies and rotational constants extracted from the depletion spectra of v'=41-50 levels were combined with the results of the previous spectroscopic study, and they were used for modifying an ab initio potential. An accuracy of 0.14% in vibrational level spacing and 0.3% in rotational constants was sufficient to predict the large observed variation in transition strengths among the vibrational levels. Our results show that transition strengths from weakly bound molecules are a good measure of the accuracy of an excited state potential.Comment: 7 pages, 7 figure

Collective Feshbach scattering of a superfluid droplet from a mesoscopic two-component Bose-Einstein condensate

We examine the collective scattering of a superfluid droplet impinging on a mesoscopic Bose-Einstein condensate (BEC) as a target. The BEC consists of an atomic gas with two internal electronic states, each of which is trapped by a finite-depth external potential. An off-resonant optical laser field provides a localized coupling between the BEC components in the trapping region. This mesoscopic scenario matches the microscopic setup for Feshbach scattering of two particles, when a bound state of one sub-manifold is embedded in the scattering continuum of the other sub-manifold. Within the mean-field picture, we obtain resonant scattering phase shifts from a linear response theory in agreement with an exact numerical solution of the real time scattering process and simple analytical approximations thereof. We find an energy-dependent transmission coefficient that is controllable via the optical field between 0 and 100%.Comment: 4 Latex pages, including 4 figure

Optical microscopy via spectral modifications of a nano-antenna

The existing optical microscopes form an image by collecting photons emitted from an object. Here we report on the experimental realization of microscopy without the need for direct optical communication with the sample. To achieve this, we have scanned a single gold nanoparticle acting as a nano-antenna in the near field of a sample and have studied the modification of its intrinsic radiative properties by monitoring its plasmon spectrum.Comment: 6 pages, 4 figures (color

Experimental observation of the Bogoliubov transformation for a Bose-Einstein condensed gas

Phonons with wavevector $q/\hbar$ were optically imprinted into a Bose-Einstein condensate. Their momentum distribution was analyzed using Bragg spectroscopy with a high momentum transfer. The wavefunction of the phonons was shown to be a superposition of +q and -q free particle momentum states, in agreement with the Bogoliubov quasiparticle picture.Comment: 4 pages, 3 figures, please take postscript version for the best version of Fig

Coherent transfer of photoassociated molecules into the rovibrational ground state

We report on the direct conversion of laser-cooled 41K and 87Rb atoms into ultracold 41K87Rb molecules in the rovibrational ground state via photoassociation followed by stimulated Raman adiabatic passage. High-resolution spectroscopy based on the coherent transfer revealed the hyperfine structure of weakly bound molecules in an unexplored region. Our results show that a rovibrationally pure sample of ultracold ground-state molecules is achieved via the all-optical association of laser-cooled atoms, opening possibilities to coherently manipulate a wide variety of molecules.Comment: 4 pages, 4 figure

Multiply quantized vortices in trapped Bose-Einstein condensates

Vortex configurations in rotating Bose-Einstein condensed gases trapped in power-law and anharmonic potentials are studied. When the confining potential is steeper than harmonic in the plane perpendicular to the axis of rotation, vortices with quantum numbers larger than one are energetically favorable if the interaction is weak enough. Features of the wave function for small and intermediate rotation frequencies are investigated numerically.Comment: 9 pages, 6 figures. Revised and extended article following referee repor