523 research outputs found
Deeply subrecoil two-dimensional Raman cooling
We report the implementation of a two-dimensional Raman cooling scheme using
sequential excitations along the orthogonal axes. Using square pulses, we have
cooled a cloud of ultracold Cesium atoms down to an RMS velocity spread of
0.39(5) recoil velocity, corresponding to an effective temperature of 30 nK
(0.15 T_rec). This technique can be useful to improve cold atom atomic clocks,
and is particularly relevant for clocks in microgravity.Comment: 8 pages, 6 figures, submitted to Phys. Rev.
Imaging the phase of an evolving Bose-Einstein condensate wavefunction
We demonstrate a spatially resolved autocorrelation measurement with a
Bose-Einstein condensate (BEC) and measure the evolution of the spatial profile
of its quantum mechanical phase. Upon release of the BEC from the magnetic
trap, its phase develops a form that we measure to be quadratic in the spatial
coordinate. Our experiments also reveal the effects of the repulsive
interaction between two overlapping BEC wavepackets and we measure the small
momentum they impart to each other
Strongly inhibited transport of a 1D Bose gas in a lattice
We report the observation of strongly damped dipole oscillations of a quantum
degenerate 1D atomic Bose gas in a combined harmonic and optical lattice
potential. Damping is significant for very shallow axial lattices (0.25 photon
recoil energies), and increases dramatically with increasing lattice depth,
such that the gas becomes nearly immobile for times an order of magnitude
longer than the single-particle tunneling time. Surprisingly, we see no
broadening of the atomic quasimomentum distribution after damped motion. Recent
theoretical work suggests that quantum fluctuations can strongly damp dipole
oscillations of 1D atomic Bose gas, providing a possible explanation for our
observations.Comment: 5 pages, 4 figure
Non-degenerate four-wave mixing in rubidium vapor: transient regime
We investigate the transient response of the generated light from Four-Wave
Mixing (FWM) in the diamond configuration using a step-down field excitation.
The transients show fast decay times and oscillations that depend on the
detunings and intensities of the fields. A simplified model taking into account
the thermal motion of the atoms, propagation, absorption and dispersion effects
shows qualitative agreement with the experimental observations with the energy
levels in rubidium (5S1/2, 5P1/2, 5P3/2 and 6S1/2). The atomic polarization
comes from all the contributions of different velocity classes of atoms in the
ensemble modifying dramatically the total transient behavior of the light from
FWM.Comment: 11 pages, 11 figures, to be published in Physical Review
Coherence properties of an atom laser
We study the coherence properties of an atom laser, which operates by
extracting atoms from a gaseous Bose-Einstein condensate via a two-photon Raman
process, by analyzing a recent experiment. We obtain good agreement with the
experimental data by solving the time-dependent Gross-Pitaevskii equation in
three dimensions both numerically and with a Thomas-Fermi model. The coherence
length is strongly affected by the space-dependent phase developed by the
condensate when the trapping potential is turned off.Comment: 11 pages, 2 Postscript figure
Neutral Plasma Oscillations at Zero Temperature
We use cold plasma theory to calculate the response of an ultracold neutral
plasma to an applied rf field. The free oscillation of the system has a
continuous spectrum and an associated damped quasimode. We show that this
quasimode dominates the driven response. We use this model to simulate plasma
oscillations in an expanding ultracold neutral plasma, providing insights into
the assumptions used to interpret experimental data [Phys. Rev. Lett. 85, 318
(2000)].Comment: 4.3 pages, including 3 figure
Coherence Properties of an Atom Laser
We study the coherence properties of an atom laser, which operates by extracting atoms from a gaseous Bose-Einstein condensate via a two-photon Raman process, by analysing a recent experiment (Hagley et al1999 Phys. Rev. Lett.833112). We obtain good agreement with the experimental data by solving the time-dependent Gross-Pitaevskii equation in three dimensions both numerically and with a Thomas-Fermi model. The coherence is strongly affected by the space-dependent phase developed by the condensate when the trapping potential is turned off
Transport of a quantum degenerate heteronuclear Bose-Fermi mixture in a harmonic trap
We report on the transport of mixed quantum degenerate gases of bosonic 87Rb
and fermionic 40K in a harmonic potential provided by a modified QUIC trap. The
samples are transported over a distance of 6 mm to the geometric center of the
anti-Helmholtz coils of the QUIC trap. This transport mechanism was implemented
by a small modification of the QUIC trap and is free of losses and heating. It
allows all experiments using QUIC traps to use the highly homogeneous magnetic
fields that can be created in the center of a QUIC trap and improves the
optical access to the atoms, e.g., for experiments with optical lattices. This
mechanism may be cascaded to cover even larger distances for applications with
quantum degenerate samples.Comment: 7 pages, 8 figure
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