175 research outputs found
Directed and Elliptic Flow in 158 AGeV Pb + Pb Collisions
Directed and elliptic flow of protons and positively charged pions has been studied in the target fragmentation region using the Plastic Ball detector in the WA98 experiment. The results exhibit a strong dependence on centrality, rapidity, and transverse momentum. The rapidity dependence can be described by a Gaussian distribution. The model comparisons reveal a large discrepancy of the flow strength obtained from the data and the simulations.Directed and elliptic flow of protons and positively charged pions has been studied in the target fragmentation region using the Plastic Ball detector in the WA98 experiment. The results exhibit a strong dependence on centrality, rapidity, and transverse momentum. The rapidity dependence can be described by a Gaussian distribution. The model comparisons reveal a large discrepancy of the flow strength obtained from the data and the simulations
Observing the emergence of chaos in a many-particle quantum system
Accessing the connection between classical chaos and quantum many-body
systems has been a long-standing experimental challenge. Here, we investigate
the onset of chaos in periodically driven two-component Bose-Einstein
condensates, whose small quantum uncertainties allow for exploring the phase
space with high resolution. By analyzing the uncertainties of time-evolved
many-body states, we find signatures of elliptic and hyperbolic periodic orbits
generated according to the Poincar\'e-Birkhoff theorem, and the formation of a
chaotic region at increasing driving strengths. The employed fluctuation
analysis allows for probing the phase-space structure by use of only short-time
quantum dynamics.Comment: 5+2 pages, 4 figure
Directed and Elliptic Flow in 158 AGeV Pb+Pb Collisions
Directed and elliptic flow of protons and positively charged pions has been
studied in the target fragmentation region using the Plastic Ball detector in
the WA98 experiment. The results exhibit a strong dependence on centrality,
rapidity, and transverse momentum.
The rapidity dependence can be described by a Gaussian distribution. The
model comparisons reveal a large discrepancy of the flow strength obtained from
the data and the simulations.Comment: 4 pages, 4 eps figures, talk at Quark Matter 99, see also
http://qgp.uni-muenster.de/WA98/qm99/flo
Transport and interaction blockade of cold bosonic atoms in a triple-well potential
We theoretically investigate the transport properties of cold bosonic atoms
in a quasi one-dimensional triple-well potential that consists of two large
outer wells, which act as microscopic source and drain reservoirs, and a small
inner well, which represents a quantum-dot-like scattering region. Bias and
gate "voltages" introduce a time-dependent tilt of the triple-well
configuration, and are used to shift the energetic level of the inner well with
respect to the outer ones. By means of exact diagonalization considering a
total number of six atoms in the triple-well potential, we find diamond-like
structures for the occurrence of single-atom transport in the parameter space
spanned by the bias and gate voltages. We discuss the analogy with Coulomb
blockade in electronic quantum dots, and point out how one can infer the
interaction energy in the central well from the distance between the diamonds.Comment: 18 pages, 6 figure
Bound and resonance states of the nonlinear Schroedinger equation in simple model systems
The stationary nonlinear Schroedinger equation, or Gross-Pitaevskii equation,
is studied for the cases of a single delta potential and a delta-shell
potential. These model systems allow analytical solutions, and thus provide
useful insight into the features of stationary bound, scattering and resonance
states of the nonlinear Schroedinger equation. For the single delta potential,
the influence of the potential strength and the nonlinearity is studied as well
as the transition from bound to scattering states. Furthermore, the properties
of resonance states for a repulsive delta-shell potential are discussed.Comment: 19 pages, 10 figure
Nonlinear transport of Bose-Einstein condensates through mesoscopic waveguides
We study the coherent flow of interacting Bose-condensed atoms in mesoscopic
waveguide geometries. Analytical and numerical methods, based on the mean-field
description of the condensate, are developed to study both stationary as well
as time-dependent propagation processes. We apply these methods to the
propagation of a condensate through an atomic quantum dot in a waveguide,
discuss the nonlinear transmission spectrum and show that resonant transport is
generally suppressed due to an interaction-induced bistability phenomenon.
Finally, we establish a link between the nonlinear features of the transmission
spectrum and the self-consistent quasi-bound states of the quantum dot.Comment: 23 pages, 16 figure
Tunnelling rates for the nonlinear Wannier-Stark problem
We present a method to numerically compute accurate tunnelling rates for a
Bose-Einstein condensate which is described by the nonlinear Gross-Pitaevskii
equation. Our method is based on a sophisticated real-time integration of the
complex-scaled Gross-Pitaevskii equation, and it is capable of finding the
stationary eigenvalues for the Wannier-Stark problem. We show that even weak
nonlinearities have significant effects in the vicinity of very sensitive
resonant tunnelling peaks, which occur in the rates as a function of the Stark
field amplitude. The mean-field interaction induces a broadening and a shift of
the peaks, and the latter is explained by analytic perturbation theory
Transport of ultracold Bose gases beyond the Gross-Pitaevskii description
We explore atom-laser-like transport processes of ultracold Bose-condensed
atomic vapors in mesoscopic waveguide structures beyond the Gross-Pitaevskii
mean-field theory. Based on a microscopic description of the transport process
in the presence of a coherent source which models the outcoupling from a
reservoir of perfectly Bose-Einstein condensed atoms, we derive a system of
coupled quantum evolution equations that describe the dynamics of a dilute
condensed Bose gas in the framework of the Hartree-Fock-Bogoliubov
approximation. We apply this method to study the transport of dilute Bose gases
through an atomic quantum dot and through waveguides with disorder. Our
numerical simulations reveal that the onset of an explictly time-dependent flow
corresponds to the appearance of strong depletion of the condensate on the
microscopic level and leads to a loss of global phase coherence.Comment: 12 pages, 7 figure
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