Demonstration of high-performance compact magnetic shields for chip-scale atomic devices.

We have designed and tested a set of five miniature nested magnetic shields constructed of high-permeability material, with external volumes for the individual shielding layers ranging from 0.01 to 2.5 cm(3). We present measurements of the longitudinal and transverse shielding factors (the ratio of external to internal magnetic field) of both individual shields and combinations of up to three layers. The largest shielding factor measured was 6 x 10(6) for a nested set of three shields, and from our results we predict a shielding factor of up to 1 x 10(13) when all five shields are used. Two different techniques were used to measure the internal field: a chip-scale atomic magnetometer and a commercially available magnetoresistive sensor. Measurements with the two methods were in good agreement.

Ultracold molecule production via a resonant oscillating magnetic field.

A novel atom-molecule conversion technique has been investigated. Ultracold 85Rb atoms sitting in a dc magnetic field near the 155 G Feshbach resonance are associated by applying a small sinusoidal oscillation to the magnetic field. There is resonant atom to molecule conversion when the modulation frequency closely matches the molecular binding energy. We observe that the atom to molecule conversion efficiency depends strongly on the frequency, amplitude, and duration of the applied modulation and on the phase space density of the sample. This technique offers high conversion efficiencies without the necessity of crossing or closely approaching the Feshbach resonance and allows precise spectroscopic measurements. Efficiencies of 55% have been observed for pure Bose-Einstein condensates.

Production efficiency of ultracold feshbach molecules in bosonic and fermionic systems.

We investigate the production efficiency of ultracold molecules in bosonic 85Rb and fermionic 40K when the magnetic field is swept across a Feshbach resonance. For adiabatic sweeps of the magnetic field, our novel model shows that the conversion efficiency of both species is solely determined by the phase space density of the atomic cloud, in contrast with a number of theoretical predictions. In the nonadiabatic regime our measurements of the 85Rb molecule conversion efficiency follow a Landau-Zener model.

Spontaneous dissociation of 85Rb Feshbach molecules.

The spontaneous dissociation of 85Rb dimers in the highest lying vibrational level has been observed in the vicinity of the Feshbach resonance that was used to produce them. The molecular lifetime shows a strong dependence on magnetic field, varying by 3 orders of magnitude between 155.5 G and 162.2 G. Our measurements are in good agreement with theoretical predictions in which molecular dissociation is driven by inelastic spin relaxation. Molecule lifetimes of tens of milliseconds can be achieved within approximately a 1 G wide region directly above the Feshbach resonance.

Experimental observation of a superfluid gyroscope in a dilute Bose-Einstein condensate.

We have observed a three-dimensional gyroscopic effect associated with a vortex in a dilute Bose-Einstein condensed gas. A condensate with a vortex possesses a single quantum of circulation, and this causes the plane of oscillation of the scissors mode to precess around the vortex line. We have measured the precession rate of the scissors oscillation. From this we deduced the angular momentum associated with the vortex line and found a value close to Planck's over 2pi per particle, as predicted for a superfluid.

Direct observation of irrotational flow and evidence of superfluidity in a rotating Bose-Einstein condensate.

We have observed the expansion of vortex-free, rotating Bose condensates after their sudden release from a slowly rotating anisotropic trap. Conservation of angular momentum, combined with the constraint of irrotational flow, cause the rotating condensate to expand in a distinctively different way to one released from a static (nonrotating) trap. This difference provides clear experimental evidence of the purely irrotational velocity field associated with a superfluid. We observed this behavior in absorption images taken along the rotation axis.

Vortex nucleation in Bose-Einstein condensates in an oblate, purely magnetic potential.

We have investigated the formation of vortices by rotating the purely magnetic potential confining a Bose-Einstein condensate. We modified the bias field of an axially symmetric TOP trap to create an elliptical potential that rotates in the radial plane. This enabled us to study the conditions for vortex nucleation over a wide range of eccentricities and rotation rates.

Temperature dependence of damping and frequency shifts of the scissors mode of a trapped Bose-Einstein condensate.

We have studied the properties of the scissors mode of a trapped Bose-Einstein condensate of 87Rb atoms at finite temperature. We measured a significant shift in the frequency of the mode below the hydrodynamic limit and a strong dependence of the damping rate as the temperature increased. We compared our damping rate results to recent theoretical calculations for other observed collective modes, finding a fair agreement. From the frequency measurements we deduce the moment of inertia of the gas and show that it is quenched below the transition point, because of the superfluid nature of the condensed gas.

Experimental observation of Beliaev coupling in a Bose-Einstein condensate.

We report the first experimental observation of Beliaev coupling between collective excitations of a Bose-Einstein condensed gas. Beliaev coupling is not predicted by the Gross-Pitaevskii equation and so this experiment tests condensate theory beyond the mean field approximation. Measurements of the amplitude of a high frequency scissors mode show that the Beliaev process transfers energy to a lower-lying mode and then back and forth between these modes, unlike Landau processes which lead to a monotonic decrease in amplitude. To enhance the Beliaev process we adjusted the geometry of the magnetic trapping potential to give a frequency ratio of 2 to 1 between the two scissors modes.

Observation of the scissors mode and evidence for superfluidity of a trapped bose-einstein condensed Gas

We report the observation of the scissors mode of a Bose-Einstein condensed gas of 87Rb atoms in a magnetic trap, which gives direct evidence of superfluidity in this system. The scissors mode of oscillation is excited by a sudden rotation of the anisotropic trapping potential. For a gas above T(c) (normal fluid) we detect the occurrence of oscillations at two frequencies, with the lower frequency corresponding to the rigid body value of the moment of inertia. Well below T(c) the condensate oscillates at a single frequency, without damping, as expected for a superfluid.

Observation of harmonic generation and nonlinear coupling in the collective dynamics of a bose-einstein condensate

We report the observation of harmonic generation and strong nonlinear coupling of two collective modes of a condensed gas of rubidium atoms. Using a modified time averaged orbiting potential trap we changed the trap anisotropy to a value where the frequency of the m = 0 high-lying mode corresponds to twice the frequency of the m = 0 low-lying mode, thus leading to strong nonlinear coupling between these modes. By changing the anisotropy of the trap and exciting the low-lying mode we observed significant frequency shifts of this fundamental mode and also the generation of its second harmonic.

The influence of drugs upon the anticoagulant activity of heparin.

Although physical incompatibility between heparin and a number of drugs has been reported we did not discover any evidence of such incompatibility when heparin was mixed with 11 commonly used drugs in therapeutic concentrations.Furthermore, there was no detectable change in the anticoagulant activity in the presence of any of these drugs, nor was there any change in the biological activity of the antibiotics tested.