7 research outputs found
Effect of optical disorder and single defects on the expansion of a Bose-Einstein condensate in a one-dimensional waveguide
We investigate the one-dimensional expansion of a Bose-Einstein condensate in
an optical guide in the presence of a random potential created with optical
speckles. With the speckle the expansion of the condensate is strongly
inhibited. A detailed investigation has been carried out varying the
experimental conditions and checking the expansion when a single optical defect
is present. The experimental results are in good agreement with numerical
calculations based on the Gross-Pitaevskii equation.Comment: 5 pages, 5 figure
Disorder-enhanced phase coherence in trapped bosons on optical lattices
The consequences of disorder on interacting bosons trapped in optical
lattices are investigated by quantum Monte Carlo simulations. At small to
moderate strengths of potential disorder a unique effect is observed: if there
is a Mott plateau at the center of the trap in the clean limit, phase coherence
{\it increases} as a result of disorder. The localization effects due to
correlation and disorder compete against each other, resulting in a partial
delocalization of the particles in the Mott region, which in turn leads to
increased phase coherence. In the absence of a Mott plateau, this effect is
absent. A detailed analysis of the uniform system without a trap shows that the
disordered states participate in a Bose glass phase.Comment: 4 pages, 4 figure
Numerical study of one-dimensional and interacting Bose-Einstein condensates in a random potential
We present a detailed numerical study of the effect of a disordered potential
on a confined one-dimensional Bose-Einstein condensate, in the framework of a
mean-field description. For repulsive interactions, we consider the
Thomas-Fermi and Gaussian limits and for attractive interactions the behavior
of soliton solutions. We find that the disorder average spatial extension of
the stationary density profile decreases with an increasing strength of the
disordered potential both for repulsive and attractive interactions among
bosons. In the Thomas Fermi limit, the suppression of transport is accompanied
by a strong localization of the bosons around the state k=0 in momentum space.
The time dependent density profiles differ considerably in the cases we have
considered. For attractive Bose-Einstein condensates, a bright soliton exists
with an overall unchanged shape, but a disorder dependent width. For weak
disorder, the soliton moves on and for a stronger disorder, it bounces back and
forth between high potential barriers.Comment: 13 pages, 13 figures, few typos correcte
Analysis of Localization Phenomena in Weakly Interacting Disordered Lattice Gases
Disorder plays a crucial role in many systems particularly in solid state
physics. However, the disorder in a particular system can usually not be chosen
or controlled. We show that the unique control available for ultracold atomic
gases may be used for the production and observation of disordered quantum
degenerate gases. A detailed analysis of localization effects for two possible
realizations of a disordered potential is presented. In a theoretical analysis
clear localization effects are observed when a superlattice is used to provide
a quasiperiodic disorder. The effects of localization are analyzed by
investigating the superfluid fraction and the localization length within the
system. The theoretical analysis in this paper paves a clear path for the
future observation of Anderson-like localization in disordered quantum gases.Comment: 9 pages, 13 figure
Experimental study of the transport of coherent interacting matter-waves in a 1D random potential induced by laser speckle
We present a detailed analysis of the 1D expansion of a coherent interacting
matterwave (a Bose-Einstein condensate) in the presence of disorder. A 1D
random potential is created via laser speckle patterns. It is carefully
calibrated and the self-averaging properties of our experimental system are
discussed. We observe the suppression of the transport of the BEC in the random
potential. We discuss the scenario of disorder-induced trapping taking into
account the radial extension in our experimental 3D BEC and we compare our
experimental results with the theoretical predictions
Mean-field phase diagram of disordered bosons in a lattice at non-zero temperature
Bosons in a periodic lattice with on-site disorder at low but non-zero
temperature are considered within a mean-field theory. The criteria used for
the definition of the superfluid, Mott insulator and Bose glass are analysed.
Since the compressibility does never vanish at non-zero temperature, it can not
be used as a general criterium. We show that the phases are unambiguously
distinguished by the superfluid density and the density of states of the
low-energy exitations. The phase diagram of the system is calculated. It is
shown that even a tiny temperature leads to a significant shift of the boundary
between the Bose glass and superfluid