4,046 research outputs found
Superfluid-insulator transition in a periodically driven optical lattice
We demonstrate that the transition from a superfluid to a Mott insulator in
the Bose-Hubbard model can be induced by an oscillating force through an
effective renormalization of the tunneling matrix element. The mechanism
involves adiabatic following of Floquet states, and can be tested
experimentally with Bose-Einstein condensates in periodically driven optical
lattices. Its extension from small to very large systems yields nontrivial
information on the condensate dynamics.Comment: 4 pages, 4 figures, RevTe
Epitaxial growth of deposited amorphous layer by laser annealing
We demonstrate that a single short pulse of laser irradiation of appropriate energy is capable of recrystallizing in open air an amorphous Si layer deposited on a (100) single-crystal substrate into an epitaxial layer. The laser pulse annealing technique is shown to overcome the interfacial oxide obstacle which usually leads to polycrystalline formation in normal thermal annealing
Tunneling control and localization for Bose-Einstein condensates in a frequency modulated optical lattice
The similarity between matter waves in periodic potential and solid-state
physics processes has triggered the interest in quantum simulation using
Bose-Fermi ultracold gases in optical lattices. The present work evidences the
similarity between electrons moving under the application of oscillating
electromagnetic fields and matter waves experiencing an optical lattice
modulated by a frequency difference, equivalent to a spatially shaken periodic
potential. We demonstrate that the tunneling properties of a Bose-Einstein
condensate in shaken periodic potentials can be precisely controlled. We take
additional crucial steps towards future applications of this method by proving
that the strong shaking of the optical lattice preserves the coherence of the
matter wavefunction and that the shaking parameters can be changed
adiabatically, even in the presence of interactions. We induce reversibly the
quantum phase transition to the Mott insulator in a driven periodic potential.Comment: Laser Physics (in press
Ground-state energy and depletions for a dilute binary Bose gas
When calculating the ground-state energy of a weakly interacting Bose gas
with the help of the customary contact pseudopotential, one meets an artifical
ultraviolet divergence which is caused by the incorrect treatment of the true
interparticle interactions at small distances. We argue that this problem can
be avoided by retaining the actual, momentum-dependent interaction matrix
elements, and use this insight for computing both the ground-state energy and
the depletions of a binary Bose gas mixture. Even when considering the
experimentally relevant case of equal masses of both species, the resulting
expressions are quite involved, and no straightforward generalizations of the
known single-species formulas. On the other hand, we demonstrate in detail how
these latter formulas are recovered from our two-species results in the limit
of vanishing interspecies interaction.Comment: 11 pages, Phys. Rev. A in pres
Quantifying and Controlling Prethermal Nonergodicity in Interacting Floquet Matter
The use of periodic driving for synthesizing many-body quantum states depends crucially on the existence of a prethermal regime, which exhibits drive-tunable properties while forestalling the effects of heating. This dependence motivates the search for direct experimental probes of the underlying localized nonergodic nature of the wave function in this metastable regime. We report experiments on a many-body Floquet system consisting of atoms in an optical lattice subjected to ultrastrong sign-changing amplitude modulation. Using a double-quench protocol, we measure an inverse participation ratio quantifying the degree of prethermal localization as a function of tunable drive parameters and interactions. We obtain a complete prethermal map of the drive-dependent properties of Floquet matter spanning four square decades of parameter space. Following the full time evolution, we observe sequential formation of two prethermal plateaux, interaction-driven ergodicity, and strongly frequency-dependent dynamics of long-time thermalization. The quantitative characterization of the prethermal Floquet matter realized in these experiments, along with the demonstration of control of its properties by variation of drive parameters and interactions, opens a new frontier for probing far-from-equilibrium quantum statistical mechanics and new possibilities for dynamical quantum engineering
Limitations of balloon sinuplasty in frontal sinus surgery
Balloon sinuplasty is a tool that is used to treat selected patients with paranasal sinus pathologies. No studies have investigated the aetiology of failed access to the frontal sinus. The aim of our study was to specify the intraoperative technical failure rate and to analyse the aetiology of the failed access to predict potential technical difficulties before surgery. We retrospectively analysed the charts of patients who underwent balloon sinuplasty from November 2007 to July 2010 at three different ENT-Centres. CT-analysis of the patients with failed access was performed. Of the 104 frontal sinuses, dilation of 12 (12%) sinuses failed. The anatomy of all failed cases revealed variations in the frontal recess (frontoethmoidal-cell, frontal-bulla-cell or agger-nasi-cell) or osteoneogenesis. In one patient, a lymphoma was overlooked during a balloon only procedure. The lymphoma was diagnosed 6months later with a biopsy during functional endoscopic sinus surgery. In complex anatomical situations of the frontal recess, balloon sinuplasty may be challenging or impossible. In these situations, it is essential to have knowledge of classical functional endoscopic sinus surgery of the frontal recess area. The drawbacks of not including a histopathologic exam should be considered in balloon only procedure
Molekulare Signalwege der aseptischen Endoprothesenlockerung (Molecular pathways in aseptic loosening of orthopaedic endoprosthesis)
Abstract Operative joint replacement to treat disabling joint conditions secondary to degenerative and inflammatory arthritides has become one of the most efficacious and cost-effective procedures to relieve pain and restore joint function. However, prosthetic implants are not built to last forever and osteolysis and aseptic loosening has been associated with prosthetic arthroplasties since their introduction. The functional life of a synthetic joint is influenced by many factors including the material of the implant, operation procedures and the surgeon involved, as well as patient-related factors. Although promising developments have been achieved in this field, more than 10% of all implants still have to undergo operative revision within 15 years after the initial operation. Failure due to sepsis, fractures and dislocations has become rare; premature loosening of implants on the other hand is becoming much more important. Prosthetic loosening without concurrent infection or trauma is called aseptic loosening. It is generally accepted that small particles ("wear debris") and activated macrophages play a key role in aseptic loosening. The pathophysiology of this condition, however, is still not very well characterized. In this article, we review the molecular mechanisms and signal pathways that were unravelled as responsible factors for loosening orthopaedic implants. Finally, we discuss possible novel strategies for future therapeutic approaches
Ultra-low threshold CW Triply Resonant OPO in the near infrared using Periodically Poled Lithium Niobate
We have operated a CW triply resonant OPO using a PPLN crystal pumped by a
Nd:YAG laser at 1.06 micron and generating signal and idler modes in the 2-2.3
micron range. The OPO was operated stably in single mode operation over large
periods of time with a pump threshold as low as 500 microwatts.Comment: 7 pages, 5 figures, submitted to JEOS
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