1,072 research outputs found
Microscopic derivation of Hubbard parameters for cold atomic gases
We study the exact solution for two atomic particles in an optical lattice
interacting via a Feshbach resonance. The analysis includes the influence of
all higher bands, as well as the proper renormalization of molecular energy in
the closed channel. Using an expansion in Bloch waves, we show that the problem
reduces to a simple matrix equation, which can be solved numerically very
efficient. This exact solution allows for the precise determination of the
parameters in the Hubbard model and the two-particle bound state energy. We
identify the regime, where a single band Hubbard model fails to describe the
scattering of the atoms as well as the bound states.Comment: 4 pages, 2 figure
Exotic Superconducting Phases of Ultracold Atom Mixtures on Triangular Lattices
We study the phase diagram of two-dimensional Bose-Fermi mixtures of
ultracold atoms on a triangular optical lattice, in the limit when the velocity
of bosonic condensate fluctuations is much larger than the Fermi velocity.
We contrast this work with our previous results for a square lattice system
in Phys. Rev. Lett. {\bf 97}, 030601 (2006).
Using functional renormalization group techniques we show that the phase
diagrams for a triangular lattice contain exotic superconducting phases. For
spin-1/2 fermions on an isotropic lattice we find a competition of -, -,
extended -, and -wave symmetry, as well as antiferromagnetic order. For
an anisotropic lattice, we further find an extended p-wave phase. A Bose-Fermi
mixture with spinless fermions on an isotropic lattice shows a competition
between - and -wave symmetry.
These phases can be traced back to the geometric shapes of the Fermi surfaces
in various regimes, as well as the intrinsic frustration of a triangular
lattice.Comment: 6 pages, 4 figures, extended version, slight modification
Spectroscopy of Superfluid Pairing in Atomic Fermi Gases
We study the dynamic structure factor for density and spin within the
crossover from BCS superfluidity of atomic fermions to the Bose-Einstein
condensation of molecules. Both structure factors are experimentally accessible
via Bragg spectroscopy, and allow for the identification of the pairing
mechanism: the spin structure factor allows for the determination of the two
particle gap, while the collective sound mode in the density structure reveals
the superfluid state.Comment: 4 pages, 3 figure
Mesoscopic Rydberg Gate based on Electromagnetically Induced Transparency
We demonstrate theoretically a parallelized C-NOT gate which allows to
entangle a mesoscopic ensemble of atoms with a single control atom in a single
step, with high fidelity and on a microsecond timescale. Our scheme relies on
the strong and long-ranged interaction between Rydberg atoms triggering
Electromagnetically Induced Transparency (EIT). By this we can robustly
implement a conditional transfer of all ensemble atoms among two logical
states, depending on the state of the control atom. We outline a many body
interferometer which allows a comparison of two many-body quantum states by
performing a measurement of the control atom.Comment: published versio
Molekulare Veränderungen beim Pankreaskarzinom
Zusammenfassung: Grundlagen: Das Pankreaskarzinom hat eine infauste Prognose. Die Ursachen für das aggressive Tumorwachstum und die frühe Metastasierung sind nur unzureichend bekannt. Mit Hilfe von modernen molekularbiologischen Untersuchungstechniken ist es in den vergangenen Jahren gelungen, einen Einblick in die Pathophysiologie dieser Erkrankung zu gewinnen. Methodik: Im Rahmen dieser Übersicht wird die pathogenetische Bedeutung von Wachstumsfaktor-Rezeptoren (EGFR, c-erbB-2, c-erbB-3), Wachstumsfaktoren (EGF, TGF-α, Amphiregulin, Betacellulin, TGF-βs, FGFs) sowie von Genmutationen (p53, K-ras) und Adhäsionsmolekülen beim humanen Pankreaskarzinom dargestellt. Ergebnisse: In einer signifikanten Anzahl der Pankreaskarzinome sind Wachstumsfaktorrezeptoren (EGFR, c-erbB-2, c-erbB-3), Wachstumsfaktoren (EGF, TGF-α, Amphiregulin, Betacellulin, TGF-βs, FGFs) und Adhäsionsmoleküle (ICAM-1, ELAM-1) überexprimiert sowie Genmutationen (p53, K-ras) vorhanden. Allerdings sind nicht alle diese molekularen Veränderungen mit einem schnelleren Tumorwachstum und einer schlechteren Prognose nach Tumorresektion vergesellschaftet. Schlußfolgerungen: Molekulare Störungen in Pankreaskarzinomzellen tragen zum malignen Phänotyp bei. Diese Veränderungen erklären, warum die Pankreaskarzinomzellen schnell proliferieren und nur eine geringe Ansprechbarkeit auf adjuvante onkologische Behandlungen zeige
Strongly correlated 2D quantum phases with cold polar molecules: controlling the shape of the interaction potential
We discuss techniques to tune and shape the long-range part of the
interaction potentials in quantum gases of polar molecules by dressing
rotational excitations with static and microwave fields. This provides a novel
tool towards engineering strongly correlated quantum phases in combination with
low dimensional trapping geometries. As an illustration, we discuss a 2D
crystalline phase, and a superfluid-crystal quantum phase transition.Comment: 4 pages, 3 figure
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