46 research outputs found
Order parameter and detection for crystallized dipolar bosons in lattices
We explore the ground-state properties of bosons with dipole-dipole
interactions in a one-dimensional optical lattice. Remarkably, a
crystallization process happens for strong dipolar interactions. Herein, we
provide a detailed characterization and a way to measure the resulting crystal
phase. Using the eigenvalues of the reduced one-body density matrix we define
an order parameter that yields a phase diagram in agreement with an analysis of
the density and two-body density. We demonstrate that the phase diagram can be
detected experimentally using the variance of single-shot measurements.Comment: 6 pages, 3 figures. Supplementary Information included. Software
available at http://ultracold.org
Detecting One-Dimensional Dipolar Bosonic Crystal Orders via Full Distribution Functions
We explore the groundstates of a few dipolar bosons in optical lattices with
incommensurate filling. The competition of kinetic, potential, and interaction
energies leads to the emergence of a variety of crystal state orders with
characteristic one- and two-body densities. We probe the transitions between
these orders and construct the emergent state diagram as a function of the
dipolar interaction strength and the lattice depth. We show that the crystal
state orders can be observed using the full distribution functions of the
particle number extracted from simulated single-shot images.Comment: 6 pages, 3 Figures in main text. Supplementary Information included.
This version accepted for publication at Physical Review Letters. Software
for the computations available at http://www.ultracold.or
Superlattice switching from parametric instabilities in a driven-dissipative BEC in a cavity
We numerically obtain the full time-evolution of a parametrically-driven
dissipative Bose-Einstein condensate in an optical cavity and investigate the
implications of driving for the phase diagram. Beyond the normal and
superradiant phases, a third nonequilibrium phase emerges as a manybody
parametric resonance. This dynamical normal phase switches between two
symmetry-broken superradiant configurations. The switching implies a breakdown
of the system's mapping to the Dicke model. Unlike the other phases, the
dynamical normal phase shows features of nonintegrability and thermalization.Comment: 5 pages, 3 figure
Condensate fragmentation as a sensitive measure of the quantum many-body behavior of bosons with long-range interactions
The occupation of more than one single-particle state and hence the emergence
of fragmentation is a many-body phenomenon universal to systems of spatially
confined interacting bosons. In the present study, we investigate the effect of
the range of the interparticle interactions on the fragmentation degree of one-
and two-dimensional systems. We solve the full many-body Schr\"odinger equation
of the system using the recursive implementation of the multiconfigurational
time-dependent Hartree for bosons method, R-MCTDHB. The dependence of the
degree of fragmentation on dimensionality, particle number, areal or line
density and interaction strength is assessed. It is found that for contact
interactions, the fragmentation is essentially density independent in two
dimensions. However, fragmentation increasingly depends on density the more
long-ranged the interactions become. The degree of fragmentation is increasing,
keeping the particle number fixed, when the density is decreasing as
expected in one spatial dimension. We demonstrate that this remains,
nontrivially, true also for long-range interactions in two spatial dimensions.
We, finally, find that within our fully self-consistent approach, the
fragmentation degree, to a good approximation, decreases universally as
when only is varied.Comment: 8 pages of RevTex4-1, 5 figure
Tunneling Dynamics in Open Ultracold Bosonic Systems
This thesis explores the quantum many-body tunneling dynamics of open ultracold bosonic systems with the recently developed multiconfigurational time-dependent Hartree for bosons (MCTDHB) method. The capabilities of MCTDHB to provide solutions to the full time-dependent many-body problem are assessed in a benchmark using the analytically solvable harmonic interaction Hamiltonian
and a generalization of it with time-dependent both one- and two-body potentials. In a comparison with numerically exact MCTDHB results, it is shown that e.g. lattice methods fail qualitatively to describe the tunneling dynamics. A
model assembling the many-body physics of the process from basic simultaneously happening single-particle processes is derived and verified with a numerically exact MCTDHB description. The generality of the model is demonstrated
even for strong interactions and large particle numbers. The ejection of the bosons from the source occurs with characteristic velocities. These velocities are
defined by the chemical potentials of systems with different particle numbers which are converted to kinetic energy. The tunneling process is accompanied by fragmentation: the ejected bosons lose their coherence with the source and among each other. It is shown that the various aspects of the tunneling dynamics’ can be controlled well with the interaction and the potential threshold
Fragmentation and correlations in a rotating Bose-Einstein condensate undergoing breakup
The theoretical investigation of rotating Bose-Einstein condensates has
mainly focused on the emergence of quantum vortex states and the condensed
properties of such systems. In the present work, we concentrate on other facets
by examining the impact of rotation on the ground state of weakly interacting
bosons confined in anharmonic potentials computed both at the mean-field level
and particularly at the many-body level of theory. For the many-body
computations, we employ the well-established many-body method known as the
multiconfigurational time-dependent Hartree method for bosons (MCTDHB). We
present how various degrees of fragmentation can be generated following the
breakup of the ground state densities in anharmonic traps without ramping up a
potential barrier for strong rotations. The breakup of the densities is found
to be associated with the acquisition of angular momentum in the condensate due
to the rotation. In addition to fragmentation, the presence of many-body
correlations is examined by computing the variances of the many-particle
position and momentum operators. For strong rotations, the many-body variances
become smaller than their mean-field counterparts, and one even finds a
scenario with opposite anisotropies of the mean-field and many-body variances.
Further, it is observed that for higher discrete symmetric systems of order k,
namely three-fold and four-fold symmetry, breakup to k sub-clouds and emergence
of k-fold fragmentation take place. All in all, we provide a thorough many-body
investigation of how and which correlations build up when a trapped
Bose-Einstein condensate breaks up under rotation