19 research outputs found
Superfluidity of Interacting Bosonic Mixtures in Optical Lattices
We report the observation of many-body interaction effects for a homonuclear
bosonic mixture in a three-dimensional optical lattice with variable state
dependence along one axis. Near the superfluid-to-Mott insulator transition for
one component, we find that the presence of a second component can reduce the
apparent superfluid coherence, most significantly when it either experiences a
strongly localizing lattice potential or none at all. We examine this effect by
varying the relative populations and lattice depths, and discuss the observed
behavior in view of recent proposals for scattering from impurities and of
atom-phonon coupling for atoms immersed in a superfluid.Comment: 4 pages, 3 figure
Collinear Four-Wave Mixing of Two-Component Matter Waves
We demonstrate atomic four-wave mixing of two-component matter waves in a
collinear geometry. Starting from a single-species Bose-Einstein condensate,
seed and pump modes are prepared through microwave state transfer and
state-selective Kapitza-Dirac diffraction. Four-wave mixing then populates the
initially empty output modes. Simulations based on a coupled-mode expansion of
the Gross-Pitaevskii equation are in very good agreement with the experimental
data. We show that four-wave mixing can play an important role in studies of
bosonic mixtures in optical lattices. Moreover our system should be of interest
in the context of quantum atom optics.Comment: 4 pages, 4 figures; revised version, essentially as publishe
Scale invariance and viscosity of a two-dimensional Fermi gas
We investigate the collective excitations of a harmonically trapped
two-dimensional Fermi gas from the collisionless (zero sound) to the
hydrodynamic (first sound) regime. The breathing mode, which is sensitive to
the equation of state, is observed at a frequency two times the dipole mode
frequency for a large range of interaction strengths and temperatures, and the
amplitude of the breathing mode is undamped. This provides evidence for a
dynamical SO(2,1) scaling symmetry of the two-dimensional Fermi gas. Moreover,
we investigate the quadrupole mode to measure the shear viscosity of the
two-dimensional gas and study its temperature dependence
Analysis of Kapitza-Dirac diffraction patterns beyond the Raman-Nath regime
We study Kapitza-Dirac diffraction of a Bose-Einstein condensate from a
standing light wave for a square pulse with variable pulse length but constant
pulse area. We find that for sufficiently weak pulses, the usual analytical
short-pulse prediction for the Raman-Nath regime continues to hold for longer
times, albeit with a reduction of the apparent modulation depth of the standing
wave. We quantitatively relate this effect to the Fourier width of the pulse,
and draw analogies to the Rabi dynamics of a coupled two-state system. Our
findings, combined with numerical modeling for stronger pulses, are of
practical interest for the calibration of optical lattices in ultracold atomic
systems
Versatile transporter apparatus for experiments with optically trapped Bose-Einstein condensates
We describe a versatile and simple scheme for producing magnetically and
optically-trapped Rb-87 Bose-Einstein condensates, based on a moving-coil
transporter apparatus. The apparatus features a TOP trap that incorporates the
movable quadrupole coils used for magneto-optical trapping and long-distance
magnetic transport of atomic clouds. As a stand-alone device, this trap allows
for the stable production of condensates containing up to one million atoms. In
combination with an optical dipole trap, the TOP trap acts as a funnel for
efficient loading, after which the quadrupole coils can be retracted, thereby
maximizing optical access. The robustness of this scheme is illustrated by
realizing the superfluid-to-Mott insulator transition in a three-dimensional
optical lattice