1,580 research outputs found
Attractive Bose-Einstein Condensates in three dimensions under rotation: Revisiting the problem of stability of the ground state in harmonic traps
We study harmonically trapped ultracold Bose gases with attractive
interparticle interactions under external rotation in three spatial dimensions
and determine the critical value of the attraction strength where the gas
collapses as a function of the rotation frequency. To this end we examine the
stationary state in the corotating frame with a many-body approach as well as
within the Gross-Pitaevskii theory of systems in traps with different
anisotropies. In contrast to recently reported results [N. A. Jamaludin, N. G.
Parker, and A. M. Martin, Phys. Rev. A \textbf{77}, 051603(R) (2008)], we find
that the collapse is not postponed in the presence of rotation. Unlike
repulsive gases, the properties of the attractive system remain practically
unchanged under rotation in isotropic and slightly anisotropic traps.Comment: 15 pages, 1 figure, 1 tabl
Phases, many-body entropy measures and coherence of interacting bosons in optical lattices
Already a few bosons with contact interparticle interactions in small optical
lattices feature a variety of quantum phases: superfluid, Mott-insulator and
fermionized Tonks gases can be probed in such systems. To detect these phases
-- pivotal for both experiment and theory -- as well as their many-body
properties we analyze several distinct measures for the one-body and many-body
Shannon information entropies. We exemplify the connection of these entropies
with spatial correlations in the many-body state by contrasting them to the
Glauber normalized correlation functions. To obtain the ground-state for
lattices with commensurate filling (i.e. an integer number of particles per
site) for the full range of repulsive interparticle interactions we utilize the
multiconfigurational time-dependent Hartree method for bosons (MCTDHB) in order
to solve the many-boson Schr\"odinger equation. We demonstrate that all
emergent phases -- the superfluid, the Mott insulator, and the fermionized gas
can be characterized equivalently by our many-body entropy measures and by
Glauber's normalized correlation functions. In contrast to our many-body
entropy measures, single-particle entropy cannot capture these transitions.Comment: 11 pages, 7 figures, software available at http://ultracold.or
Optimized observable readout from single-shot images of ultracold atoms via machine learning
Single-shot images are the standard readout of experiments with ultracold atoms, the imperfect reflection of their many-body physics. The efficient extraction of observables from single-shot images is thus crucial. Here we demonstrate how artificial neural networks can optimize this extraction. In contrast to standard averaging approaches, machine learning allows both one- and two-particle densities to be accurately obtained from a drastically reduced number of single-shot images. Quantum fluctuations and correlations are directly harnessed to obtain physical observables for bosons in a tilted double-well potential at an extreme accuracy. Strikingly, machine learning also enables a reliable extraction of momentum-space observables from real-space single-shot images and vice versa. With this technique, the reconfiguration of the experimental setup between in situ and time-of-flight imaging is required only once to obtain training data, thus potentially granting an outstanding reduction in resources
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