162 research outputs found
Non-equilibrium coherence dynamics of a soft boson lattice
We study the non-equilibrium evolution of the phase coherence of a
Bose-Einstein condensate (BEC) in a one dimensional optical lattice, as the
lattice is suddenly quenched from an insulating to a superfluid state. We
observe slowly damped phase coherence oscillations in the regime of large
filling factor (~100 bosons per site) at a frequency proportional to the
generalized Josephson frequency. The truncated Wigner approximation (TWA)
predicts the frequency of the observed oscillations.Comment: 10 pages. 4 figure
Transport behaviour of a Bose Einstein condensate in a bichromatic optical lattice
The Bloch and dipole oscillations of a Bose Einstein condensate (BEC) in an
optical superlattice is investigated. We show that the effective mass increases
in an optical superlattice, which leads to localization of the BEC, in
accordance with recent experimental observations [16]. In addition, we find
that the secondary optical lattice is a useful additional tool to manipulate
the dynamics of the atoms.Comment: Modified manuscrip
Superfluid current disruption in a chain of weakly coupled Bose-Einstein Condensates
We report the experimental observation of the disruption of the superfluid
atomic current flowing through an array of weakly linked Bose-Einstein
condensates. The condensates are trapped in an optical lattice superimposed on
a harmonic magnetic potential. The dynamical response of the system to a change
of the magnetic potential minimum along the optical lattice axis goes from a
coherent oscillation (superfluid regime) to a localization of the condensates
in the harmonic trap ("classical" insulator regime). The localization occurs
when the initial displacement is larger than a critical value or, equivalently,
when the velocity of the wavepacket's center of mass is larger than a critical
velocity dependent on the tunnelling rate between adjacent sites.Comment: 8 pages, 4 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
Thermodynamics of quantum degenerate gases in optical lattices
The entropy-temperature curves are calculated for non-interacting Bose and
Fermi gases in a 3D optical lattice. These curves facilitate understanding of
how adiabatic changes in the lattice depth affect the temperature, and we
demonstrate regimes where the atomic sample can be significantly heated or
cooled by the loading process. We assess the effects of interactions on a Bose
gas in a deep optical lattice, and show that interactions ultimately limit the
extent of cooling that can occur during lattice loading.Comment: 6 pages, 4 figures. Submitted to proceedings of Laser Physics 2006
Worksho
Detecting Super-Counter-Fluidity by Ramsey Spectroscopy
Spatially selective Ramsey spectroscopy is suggested as a method for
detecting the super-counter-fluidity of two-component atomic mixture in optical
lattice.Comment: 3pages, no figures, replaced with revised version accepted by PRA.
Discussion of the Ramsey pattern specific for topological excitations is
adde
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
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
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