100 research outputs found
Macroscopic dynamics of a trapped Bose-Einstein condensate in the presence of 1D and 2D optical lattices
The hydrodynamic equations of superfluids for a weakly interacting Bose gas
are generalized to include the effects of periodic optical potentials produced
by stationary laser beams. The new equations are characterized by a
renormalized interaction coupling constant and by an effective mass accounting
for the inertia of the system along the laser direction. For large laser
intensities the effective mass is directly related to the tunneling rate
between two consecutive wells. The predictions for the frequencies of the
collective modes of a condensate confined by a magnetic harmonic trap are
discussed for both 1D and 2D optical lattices and compared with recent
experimental data.Comment: 4 pages, 2 postscript figure
Mott insulators in an optical lattice with high filling factors
We discuss the superfluid to Mott insulator transition of an atomic Bose gas
in an optical lattice with high filling factors. We show that also in this
multi-band situation, the long-wavelength physics is described by a single-band
Bose-Hubbard model. We determine the many-body renormalization of the tunneling
and interaction parameters in the effective Bose-Hubbard Hamiltonian, and
consider the resulting model at nonzero temperatures. We show that in
particular for a one or two-dimensional optical lattice, the Mott insulator
phase is more difficult to realize than anticipated previously.Comment: 5 pages, 3 figures, title changed, major restructuring, resubmitted
to PR
Bragg spectroscopy of a cigar shaped Bose condensate in optical lattices
We study properties of excited states of an array of weakly coupled
quasi-two-dimensional Bose condensates by using the hydrodynamic theory. We
calculate multibranch Bogoliubov-Bloch spectrums and its corresponding
eigenfunctions. The spectrum of the axial excited states and its eigenfunctions
strongly depends on the coupling among various discrete radial modes within a
given symmetry. This mode coupling is due to the presence of radial trapping
potential. The multibranch nature of the Bogoliubov-Bloch spectrum and its
dependence on the mode-coupling can be realized by analyzing dynamic structure
factor and momentum transferred to the system in Bragg spectroscopy
experiments. We also study dynamic structure factor and momentum transferred to
the condensate due to the Bragg spectroscopy experiment.Comment: 7 pages, 5 figures, to appear in Journal of Physics B: Atomic,
Molecular & Optical Physic
Ferromagnetism in a lattice of Bose condensates
We show that an ensemble of spinor Bose-Einstein condensates confined in a
one dimensional optical lattice can undergo a ferromagnetic phase transition
and spontaneous magnetization arises due to the magnetic dipole-dipole
interaction. This phenomenon is analogous to ferromagnetism in solid state
physics, but occurs with bosons instead of fermions.Comment: 4 pages, 2 figure
Plasma Oscillations and Expansion of an Ultracold Neutral Plasma
We report the observation of plasma oscillations in an ultracold neutral
plasma. With this collective mode we probe the electron density distribution
and study the expansion of the plasma as a function of time. For classical
plasma conditions, i.e. weak Coulomb coupling, the expansion is dominated by
the pressure of the electron gas and is described by a hydrodynamic model.
Discrepancies between the model and observations at low temperature and high
density may be due to strong coupling of the electrons.Comment: 4 pages, 4 figures. Accepted Phys. Rev. Let
Quantum Kinetic Theory of BEC Lattice Gas:Boltzmann Equations from 2PI-CTP Effective Action
We continue our earlier work [Ana Maria Rey, B. L. Hu, Esteban Calzetta,
Albert Roura and Charles W. Clark, Phys. Rev. A 69, 033610 (2004)] on the
nonequilibrium dynamics of a Bose Einstein condensate (BEC) selectively loaded
into every third site of a one-dimensional optical lattice. From the
two-particle irreducible (2PI) closed-time-path (CTP) effective action for the
Bose- Hubbard Hamiltonian, we show how to obtain the Kadanoff-Baym equations of
quantum kinetic theory. Using the quasiparticle approximation, we show that the
local equilibrium solutions of these equations reproduce the second- order
corrections to the self-energy originally derived by Beliaev. This work paves
the way for the use of effective action methods in the derivation of quantum
kinetic theory of many atom systems.Comment: 21 pages, 0 figures, minor editorial changes were mad
A white-light trap for Bose-Einstein condensates
We propose a novel method for trapping Bose-condensed atoms using a
white-light interference fringe. Confinement frequencies of tens of kHz can be
achieved in conjunction with trap depths of only a few micro-K. We estimate
that lifetimes on the order of 10 s can be achieved for small numbers of atoms.
The tight confinement and shallow depth permit tunneling processes to be used
for studying interaction effects and for applications in quantum information.Comment: 10 pages with 3 figure
Superfluid to Mott insulator transition in one, two, and three dimensions
We have created one-, two-, and three-dimensional quantum gases and study the
superfluid to Mott insulator transition. Measurements of the transition using
Bragg spectroscopy show that the excitation spectra of the low-dimensional
superfluids differ significantly from the three-dimensional case
Insulator-Superfluid transition of spin-1 bosons in an optical lattice in magnetic field
We study the insulator-superfluid transition of spin-1 bosons in an optical
lattice in a uniform magnetic field. Based on a mean-field approximation we
obtained a zero-temperature phase diagram. We found that depending on the
particle number the transition for bosons with antiferromagnetic interaction
may occur into different superfluid phases with spins aligned along or opposite
to the field direction. This is qualitatively different from the field-free
transition for which the mean-field theory predicts a unique (polar) superfluid
state for any particle number.Comment: 10 pages, 2 eps figure
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