668 research outputs found
Collective Feshbach scattering of a superfluid droplet from a mesoscopic two-component Bose-Einstein condensate
We examine the collective scattering of a superfluid droplet impinging on a
mesoscopic Bose-Einstein condensate (BEC) as a target. The BEC consists of an
atomic gas with two internal electronic states, each of which is trapped by a
finite-depth external potential. An off-resonant optical laser field provides a
localized coupling between the BEC components in the trapping region. This
mesoscopic scenario matches the microscopic setup for Feshbach scattering of
two particles, when a bound state of one sub-manifold is embedded in the
scattering continuum of the other sub-manifold. Within the mean-field picture,
we obtain resonant scattering phase shifts from a linear response theory in
agreement with an exact numerical solution of the real time scattering process
and simple analytical approximations thereof. We find an energy-dependent
transmission coefficient that is controllable via the optical field between 0
and 100%.Comment: 4 Latex pages, including 4 figure
Formation of Pairing Fields in Resonantly Coupled Atomic and Molecular Bose-Einstein Condensates
In this paper, we show that pair-correlations may play an important role in
the quantum statistical properties of a Bose-Einstein condensed gas composed of
an atomic field resonantly coupled with a corresponding field of molecular
dimers. Specifically, pair-correlations in this system can dramatically modify
the coherent and incoherent transfer between the atomic and molecular fields.Comment: 4 pages, 4 figure
Equivalence of Kinetic Theories of Bose-Einstein Condensation
We discuss the equivalence of two non-equilibrium kinetic theories that
describe the evolution of a dilute, Bose-Einstein condensed atomic gas in a
harmonic trap. The second-order kinetic equations of Walser et al. [PRA 63,
013607 (2001)] reduce to the Gross-Pitaevskii equation and the quantum
Boltzmann equation in the low and high temperature limits, respectively. These
kinetic equations can thus describe the system in equilibrium (finite
temperature) as well as in non-equilibrium (real time). We have found this
theory to be equivalent to the non-equilibrium Green's function approach
originally proposed by Kadanoff and Baym and more recently applied to
inhomogeneous trapped systems by M. Imamovi\'c-Tomasovi\'c and A. Griffin
[arXiv:cond-mat/9911402].Comment: REVTeX3, 6 pages, 2 eps figures, published version, minor change
Dropping cold quantum gases on Earth over long times and large distances
We describe the non-relativistic time evolution of an ultra-cold degenerate
quantum gas (bosons/fermions) falling in Earth's gravity during long times (10
sec) and over large distances (100 m). This models a drop tower experiment that
is currently performed by the QUANTUS collaboration at ZARM (Bremen, Germany).
Starting from the classical mechanics of the drop capsule and a single particle
trapped within, we develop the quantum field theoretical description for this
experimental situation in an inertial frame, the corotating frame of the Earth,
as well as the comoving frame of the drop capsule. Suitable transformations
eliminate non-inertial forces, provided all external potentials (trap, gravity)
can be approximated with a second order Taylor expansion around the
instantaneous trap center. This is an excellent assumption and the harmonic
potential theorem applies. As an application, we study the quantum dynamics of
a cigar-shaped Bose-Einstein condensate in the Gross-Pitaevskii mean-field
approximation. Due to the instantaneous transformation to the rest-frame of the
superfluid wave packet, the long-distance drop (100m) can be studied easily on
a numerical grid.Comment: 18 pages latex, 5 eps figures, submitte
A microscopic quantum dynamics approach to the dilute condensed Bose gas
We derive quantum evolution equations for the dynamics of dilute condensed
Bose gases. The approach contains, at different orders of approximation, for
cases close to equilibrium, the Gross Pitaevskii equation and the first order
Hartree Fock Bogoliubov theory. The proposed approach is also suited for the
description of the dynamics of condensed gases which are far away from
equilibrium. As an example the scattering of two Bose condensates is discussed.Comment: 8 pages, submitted to Phys. Rev.
Reconstruction of metabolic networks from high-throughput metabolite profiling data: in silico analysis of red blood cell metabolism
We investigate the ability of algorithms developed for reverse engineering of
transcriptional regulatory networks to reconstruct metabolic networks from
high-throughput metabolite profiling data. For this, we generate synthetic
metabolic profiles for benchmarking purposes based on a well-established model
for red blood cell metabolism. A variety of data sets is generated, accounting
for different properties of real metabolic networks, such as experimental
noise, metabolite correlations, and temporal dynamics. These data sets are made
available online. We apply ARACNE, a mainstream transcriptional networks
reverse engineering algorithm, to these data sets and observe performance
comparable to that obtained in the transcriptional domain, for which the
algorithm was originally designed.Comment: 14 pages, 3 figures. Presented at the DIMACS Workshop on Dialogue on
Reverse Engineering Assessment and Methods (DREAM), Sep 200
Finite-temperature simulations of the scissors mode in Bose-Einstein condensed gases
The dynamics of a trapped Bose-condensed gas at finite temperatures is
described by a generalized Gross-Pitaevskii equation for the condensate order
parameter and a semi-classical kinetic equation for the thermal cloud, solved
using -body simulations. The two components are coupled by mean fields as
well as collisional processes that transfer atoms between the two. We use this
scheme to investigate scissors modes in anisotropic traps as a function of
temperature. Frequency shifts and damping rates of the condensate mode are
extracted, and are found to be in good agreement with recent experiments.Comment: 4 pages, 3 figure
Nonlinear Josephson-type oscillations of a driven, two-component Bose-Einstein condensate
We propose an experiment that would demonstrate nonlinear Josephson-type
oscillations in the relative population of a driven, two-component
Bose-Einstein condensate. An initial state is prepared in which two condensates
exist in a magnetic trap, each in a different hyperfine state, where the
initial populations and relative phase between condensates can be controlled
within experimental uncertainty. A weak driving field is then applied, which
couples the two internal states of the atom and consequently transfers atoms
back and forth between condensates. We present a model of this system and
investigate the effect of the mean field on the dynamical evolution.Comment: 4 pages, 3 fig
The stochastic Gross-Pitaevskii equation II
We provide a derivation of a more accurate version of the stochastic
Gross-Pitaevskii equation, as introduced by Gardiner et al. (J. Phys. B
35,1555,(2002). The derivation does not rely on the concept of local energy and
momentum conservation, and is based on a quasi-classical Wigner function
representation of a "high temperature" master equation for a Bose gas, which
includes only modes below an energy cutoff E_R that are sufficiently highly
occupied (the condensate band). The modes above this cutoff (the non-condensate
band) are treated as being essentially thermalized. The interaction between
these two bands, known as growth and scattering processes, provide noise and
damping terms in the equation of motion for the condensate band, which we call
the stochastic Gross-Pitaevskii equation. This approach is distinguished by the
control of the approximations made in its derivation, and by the feasibility of
its numerical implementation.Comment: 24 pages of LaTeX, one figur
Interferometry with Bose-Einstein Condensates in Microgravity
Atom interferometers covering macroscopic domains of space-time are a
spectacular manifestation of the wave nature of matter. Due to their unique
coherence properties, Bose-Einstein condensates are ideal sources for an atom
interferometer in extended free fall. In this paper we report on the
realization of an asymmetric Mach-Zehnder interferometer operated with a
Bose-Einstein condensate in microgravity. The resulting interference pattern is
similar to the one in the far-field of a double-slit and shows a linear scaling
with the time the wave packets expand. We employ delta-kick cooling in order to
enhance the signal and extend our atom interferometer. Our experiments
demonstrate the high potential of interferometers operated with quantum gases
for probing the fundamental concepts of quantum mechanics and general
relativity.Comment: 8 pages, 3 figures; 8 pages of supporting materia
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