Avoided level crossing spectroscopy with dressed matter waves

We devise a method for probing resonances of macroscopic matter waves in shaken optical lattices by monitoring their response to slow parameter changes, and show that such resonances can be disabled by particular choices of the driving amplitude. The theoretical analysis of this scheme reveals far-reaching analogies between dressed atoms and time-periodically forced matter waves.Comment: 4 pages, 3 figure

Describing many-body localized systems in thermal environments

In this work we formulate an efficient method for the description of fully many-body localized systems in weak contact with thermal environments at temperature T. The key idea is to exploit the representation of the system in terms of quasi-local integrals of motion (l-bits) to efficiently derive the generator for the quantum master equation in Born-Markov approximation. We, moreover, show how to compute the steady state of this equation efficiently by using quantum-jump Monte-Carlo techniques as well as by deriving approximate kinetic equations of motion. As an example, we consider a one-dimensional disordered extended Hubbard model for spinless fermions, for which we derive the l-bit representation approximately by employing a recently proposed method valid in the limit of strong disorder and weak interactions. Coupling the system to a global thermal bath, we study the transport between two leads with different chemical potentials at both of its ends. We find that the temperature-dependent current is captured by an interaction-dependent version of Mott's law for variable range hopping, where transport is enhanced/lowered depending on whether the interactions are attractive or repulsive, respectively. We interpret these results in terms of spatio-energetic correlations between the l-bits

Development of a Computationally Efficient Fabric Model for Optimization of Gripper Trajectories in Automated Composite Draping

An automated prepreg fabric draping system is being developed which consists of an array of actuated grippers. It has the ability to pick up a fabric ply and place it onto a double-curved mold surface. A previous research effort based on a nonlinear Finite Element model showed that the movements of the grippers should be chosen carefully to avoid misplacement and induce of wrinkles in the draped configuration. Thus, the present study seeks to develop a computationally efficient model of the mechanical behavior of a fabric based on 2D catenaries which can be used for optimization of the gripper trajectories. The model includes bending stiffness, large deflections, large ply shear and a simple contact formulation. The model is found to be quick to evaluate and gives very reasonable predictions of the displacement field

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

Analog of photon-assisted tunneling in a Bose-Einstein condensate

We study many-body tunneling of a small Bose-Einstein condensate in a periodically modulated, tilted double-well potential. Periodic modulation of the trapping potential leads to an analog of photon-assisted tunneling, with distinct signatures of the interparticle interaction visible in the amount of particles transferred from one well to the other. In particular, under experimentally accessible conditions there exist well-developed half-integer Shapiro-like resonances.Comment: 4 pages, 4 figures, RevTe

Generation of chirp-free picosecond pulses

The frequency spectrum of moderately chirped laser pulses depends upon the portion of the beam which is accepted by the spectrometer. Observation of the development of the chirp in a mode-locked pulse train allows to determine the small incipient chirp of early pulses. A product, bandwidth times pulse duration, of 0.47 ± 0.03 is consistently observed for single pulses switched from a passively mode-locked Nd-glass system