arXiv subjects

R. Grimm

Publications and source records attributed to R. Grimm.

71 records · Page 4Linked to original sources

arXiv2003

Two-dimensional Bose-Einstein condensate in an optical surface trap

We report on the creation of a two-dimensional Bose-Einstein condensate of cesium atoms in a gravito-optical surface trap. The condensate is produced a few micrometer above a dielectric surface on an evanescent-wave atom mirror. After evaporative cooling by all-optical means, expansion measurements for the tightly confined vertical motion show energies well below the vibrational energy quantum. The presence of a condensate is observed in two independent ways by a magnetically induced collapse at negative scattering length and by measurements of the horizontal expansion.

cond-mat.soft↗

arXiv2003

Pure Gas of Optically Trapped Molecules Created from Fermionic Atoms

We report on the production of a pure sample of up to 3x10^5 optically trapped molecules from a Fermi gas of 6Li atoms. The dimers are formed by three-body recombination near a Feshbach resonance. For purification a Stern-Gerlach selection technique is used that efficiently removes all trapped atoms from the atom-molecule mixture. The behavior of the purified molecular sample shows a striking dependence on the applied magnetic field. For very weakly bound molecules near the Feshbach resonance, the gas exhibits a remarkable stability with respect to collisional decay.

cond-mat.soft↗

arXiv2002

Evanescent-wave trapping and evaporative cooling of an atomic gas near two-dimensionality

A dense gas of cesium atoms at the crossover to two-dimensionality is prepared in a highly anisotropic surface trap that is realized with two evanescent light waves. Temperatures as low as 100nK are reached with 20.000 atoms at a phase-space density close to 0.1. The lowest quantum state in the tightly confined direction is populated by more than 60%. The system offers intriguing prospects for future experiments on degenerate quantum gases in two dimensions.

physics.gen-ph↗

arXiv2002

Magnetic field control of elastic scattering in a cold gas of fermionic lithium atoms

We study elastic collisions in an optically trapped spin mixture of fermionic lithium atoms in the presence of magnetic fields up to 1.5kG by measuring evaporative loss. Our experiments confirm the expected magnetic tunability of the scattering length by showing the main features of elastic scattering according to recent calculations. We measure the zero crossing of the scattering length that is associated with a predicted Feshbach resonance at 530(3)G. Beyond the resonance we observe the expected large cross section in the triplet scattering regime.

physics.atom-ph↗

arXiv2002

Cold atom gas at very high densities in an optical surface microtrap

An optical microtrap is realized on a dielectric surface by crossing a tightly focused laser beam with an horizontal evanescent-wave atom mirror. The nondissipative trap is loaded with $\sim$$10^5$ cesium atoms through elastic collisions from a cold reservoir provided by a large-volume optical surface trap. With an observed 300-fold local increase of the atomic number density approaching $10^{14}{\rm cm}^{-3}$, unprecedented conditions of cold atoms close to a surface are realized.

physics.atom-ph↗

arXiv2001

Sympathetic Cooling with Two Atomic Species in an Optical Trap

We simultaneously trap ultracold lithium and cesium atoms in an optical dipole trap formed by the focus of a CO$_2$ laser and study the exchange of thermal energy between the gases. The cesium gas, which is optically cooled to $20 μ$K, efficiently decreases the temperature of the lithium gas through sympathetic cooling. The measured cross section for thermalizing $^{133}$Cs-$^7$Li collisions is $8 \times 10^{-12}$ cm$^2$, for both species in their lowest hyperfine ground state. Besides thermalization, we observe evaporation of lithium purely through elastic cesium-lithium collisions (sympathetic evaporation).

physics.atom-ph↗

arXiv2001

Mixture of ultracold lithium and cesium atoms in an optical dipole trap

We present the first simultaneous trapping of two different ultracold atomic species in a conservative trap. Lithium and cesium atoms are stored in an optical dipole trap formed by the focus of a CO$_2$ laser. Techniques for loading both species of atoms are discussed and observations of elastic and inelastic collisions between the two species are presented. A model for sympathetic cooling of two species with strongly different mass in the presence of slow evaporation is developed. From the observed Cs-induced evaporation of Li atoms we estimate a cross section for cold elastic Li-Cs collisions.

physics.atom-ph↗

arXiv2001

Sympathetic Cooling of Lithium by Laser-cooled Cesium

We present first indications of sympathetic cooling between two neutral, optically trapped atomic species. Lithium and cesium atoms are simultaneously stored in an optical dipole trap formed by the focus of a CO$_2$ laser, and allowed to interact for a given period of time. The temperature of the lithium gas is found to decrease when in thermal contact with cold cesium. The timescale of thermalization yields an estimate for the Li-Cs cross-section.

physics.atom-ph↗

arXiv2001

Resonator-Enhanced Optical Dipole Trap for Fermionic Lithium Atoms

We demonstrate a novel optical dipole trap which is based on the enhancement of the optical power density of a Nd:YAG laser beam in a resonator. The trap is particularly suited for experiments with ultracold gases, as it combines a potential depth of order 1 mK with storage times of several tens of seconds. We study the interactions in a gas of fermionic lithium atoms in our trap and observe the influence of spin-changing collisions and off-resonant photon scattering. A key element in reaching long storage times is an ultra-low noise laser. The dependence of the storage time on laser noise is investigated.

physics.atom-ph↗

arXiv2000

Evaporative cooling of cesium atoms in the gravito-optical surface trap

We report on cooling of an atomic cesium gas closely above an evanescent-wave. Our first evaporation experiments show a temperature reduction from 10muK down to 300nK along with a gain in phase-space density of almost two orders of magnitude. In a series of measurements of heating and spin depolarization an incoherent background of resonant photons in the evanescent-wave diode laser light was found to be the limiting factor at this stage.

physics.atom-ph↗

arXiv2000

Supergravity couplings: a geometric formulation

This report provides a pedagogical introduction to the description of the general Poincare supergravity/matter/Yang-Mills couplings using methods of Kahler superspace geometry. At a more advanced level this approach is generalized to include tensor field and Chern-Simons couplings in supersymmetry and supergravity, relevant in the context of weakly and strongly coupled string theories.

hep-th↗

arXiv2000

Optical and evaporative cooling of cesium atoms in the gravito-optical surface trap

We report on cooling of an atomic cesium gas closely above an evanescent-wave atom mirror. At high densitities, optical cooling based on inelastic reflections is found to be limited by a density-dependent excess temperature and trap loss due to ultracold collisions involving repulsive molecular states. Nevertheless, very good starting conditions for subsequent evaporative cooling are obtained. Our first evaporation experiments show a temperature reduction from 10muK down to 300nK along with a gain in phase-space density of almost two orders of magnitude.

physics.atom-ph↗

arXiv2000

Very long storage times and evaporative cooling of cesium atoms in a quasi-electrostatic dipole trap

We have trapped cesium atoms over many minutes in the focus of a CO$_2$-laser beam employing an extremely simple laser system. Collisional properties of the unpolarized atoms in their electronic ground state are investigated. Inelastic binary collisions changing the hyperfine state lead to trap loss which is quantitatively analyzed. Elastic collisions result in evaporative cooling of the trapped gas from 25 $μ$K to 10 $μ$K over a time scale of about 150 s.

physics.atom-ph↗

arXiv1999

Cold inelastic collisions between lithium and cesium in a two-species magneto-optical trap

We investigate collisional properties of lithium and cesium which are simultaneously confined in a combined magneto-optical trap. Trap-loss collisions between the two species are comprehensively studied. Different inelastic collision channels are identified, and inter-species rate coefficients as well as cross sections are determined. It is found that loss rates are independent of the optical excitation of Li, as a consequence of the repulsive Li$^*$-Cs interaction. Li and Cs loss by inelastic inter-species collisions can completely be attributed to processes involving optically excited cesium (fine-structure changing collisions and radiative escape). By lowering the trap depth for Li, an additional loss channel of Li is observed which results from ground-state Li-Cs collisions changing the hyperfine state of cesium.

physics.atom-ph↗

arXiv1998

N=2 central charge superspace and a minimal supergravity multiplet

We extend the notion of central charge superspace to the case of local supersymmetry. Gauged central charge transformations are identified as diffeomorphisms at the same footing as space-time diffeomorphisms and local supersymmetry transformations. Given the general structure we then proceed to the description of a particular vector-tensor supergravity multiplet of 24+24 components, identified by means of rather radical constraints.

hep-th↗

arXiv1996

The 3-Form Multiplet in Supergravity

We derive the couplings of the 3-form supermultiplet to the general supergravity-matter-Yang-Mills system. Based on the methods of superspace geometry, we identify component fields, establish their supergravity transformations and construct invariant component field actions. Two specific applications are adressed: the appearance of fundamental 3-forms in the context of strong-weak duality and the use of the 3-form supermultiplets to describe effective degrees of freedom relevant to the mechanism of gaugino condensation.

hep-th↗

arXiv1995

Supergravity, Linear Multiplets, and Chern-Simons Forms

Some general features of locally supersymmetric theories (N=1 in four dimensions) involving Chern-Simons forms and antisymmetric tensors are sketched out. The relevance of the three-form multiplet both for the description of Chern-Simons forms and the supersymmetry properties of the gaugino condensate is pointed out.

hep-th↗