625 research outputs found
Subdiffusion of nonlinear waves in quasiperiodic potentials
We study the spatio-temporal evolution of wave packets in one-dimensional
quasiperiodic lattices which localize linear waves. Nonlinearity (related to
two-body interactions) has destructive effect on localization, as recently
observed for interacting atomic condensates [Phys. Rev. Lett. 106, 230403
(2011)]. We extend the analysis of the characteristics of the subdiffusive
dynamics to large temporal and spatial scales. Our results for the second
moment consistently reveal an asymptotic and
intermediate laws. At variance to purely random systems
[Europhys. Lett. 91, 30001 (2010)] the fractal gap structure of the linear wave
spectrum strongly favors intermediate self-trapping events. Our findings give a
new dimension to the theory of wave packet spreading in localizing
environments
Correlation function of weakly interacting bosons in a disordered lattice
One of the most important issues in disordered systems is the interplay of
the disorder and repulsive interactions. Several recent experimental advances
on this topic have been made with ultracold atoms, in particular the
observation of Anderson localization, and the realization of the disordered
Bose-Hubbard model. There are however still questions as to how to
differentiate the complex insulating phases resulting from this interplay, and
how to measure the size of the superfluid fragments that these phases entail.
It has been suggested that the correlation function of such a system can give
new insights, but so far little experimental investigation has been performed.
Here, we show the first experimental analysis of the correlation function for a
weakly interacting, bosonic system in a quasiperiodic lattice. We observe an
increase in the correlation length as well as a change in shape of the
correlation function in the delocalization crossover from Anderson glass to
coherent, extended state. In between, the experiment indicates the formation of
progressively larger coherent fragments, consistent with a fragmented BEC, or
Bose glass.Comment: 16 pages, 8 figure
Exponential localization in one-dimensional quasiperiodic optical lattices
We investigate the localization properties of a one-dimensional bichromatic
optical lattice in the tight binding regime, by discussing how exponentially
localized states emerge upon changing the degree of commensurability. We also
review the mapping onto the discrete Aubry-Andre' model, and provide evidences
on how the momentum distribution gets modified in the crossover from extended
to exponentially localized states. This analysis is relevant to the recent
experiment on Anderson localization of a noninteracting Bose-Einstein
condensate in a quasiperiodic optical lattice [G. Roati et al., Nature 453, 895
(2008)].Comment: 13 pages, 6 figure
Spinor-Induced Instability of Kinks, Holes and Quantum Droplets
We address the existence and stability of one-dimensional (1D) holes and
kinks and two-dimensional (2D) vortex-holes nested in extended binary Bose
mixtures, which emerge in the presence of Lee-Huang-Yang (LHY) quantum
corrections to the mean-field energy, along with self-bound quantum droplets.
We consider both the symmetric system with equal intra-species scattering
lengths and atomic masses, modeled by a single (scalar) LHY-corrected
Gross-Pitaevskii equation (GPE), and the general asymmetric case with different
intra-species scattering lengths, described by two coupled (spinor) GPEs. We
found that in the symmetric setting, 1D and 2D holes can exist in a stable form
within a range of chemical potentials that overlaps with that of self-bound
quantum droplets, but that extends far beyond it. In this case, holes are found
to be stable in 1D and they transform into pairs of stable out-of-phase kinks
at the critical chemical potential at which localized droplets turn into
flat-top states, thereby revealing the connection between localized and
extended nonlinear states. In contrast, spinor nature of the asymmetric systems
may lead to instability of 1D holes, which tend to break into two gray states
moving in the opposite directions. Such instability arises due to spinor nature
of the system and it affects only holes nested in extended
modulationally-stable backgrounds, while localized quantum droplet families
remain completely stable, even in the asymmetric case, while 1D holes remain
stable only close to the point where they transform into pairs of kinks. We
also found that symmetric systems allow fully stable 2D vortex-carrying
single-charge states at moderate amplitudes, while unconventional instabilities
appear also at high amplitudes. Symmetry also strongly inhibits instabilities
for double-charge vortex-holes, which thus exhibit unexpectedly robust
evolutions at low amplitudes.Comment: 9 pages, 7 figures, to appear in New Journal of Physic
Radio Frequency Selective Addressing of Localized Particles in a Periodic Potential
We study the localization and addressability of ultra cold atoms in a
combined parabolic and periodic potential. Such a potential supports the
existence of localized stationary states and we show that using a radio
frequency field allows to selectively address the atoms in these states. This
method is used to measure the energy and momentum distribution of the atoms in
the localized states. We also discuss possible extensions of this scheme to
address and manipulate particles in single lattice sites.Comment: 4 pages, 4 figure
Detecting phonons and persistent currents in toroidal Bose-Einstein condensates by means of pattern formation
We theoretically investigate the dynamic properties of a Bose-Einstein
condensate in a toroidal trap. A periodic modulation of the transverse
confinement is shown to produce a density pattern due to parametric
amplification of phonon pairs. By imaging the density distribution after free
expansion one obtains i) a precise determination of the Bogoliubov spectrum and
ii) a sensitive detection of quantized circulation in the torus. The parametric
amplification is also sensitive to thermal and quantum fluctuations.Comment: 4 pages, 4 figures; new figures, revised version to appear as a Rapid
Communication in Physical Review
- …